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1. Fig 6 3 Current mirror Since the bases are connected together both transistors have the same value of Vgeg and thus their collector currents will match if they have matching values of J and and are at the same temperature In practice there will always be a slight current mismatch since the programming current includes the base currents of Q4 and Qs and the output current does not Also since 6 increases with Vcg and Vgg at a given collector current depends slightly on Vcg called the Early effect the current mismatch will depend on the output voltage You can explore this using a variable load as shown in Fig 6 3 Monitor the collector voltage as you adjust the load resistance gt How does the output current vary with collector voltage What is the approximate dynamic resistance of the output Is this a better or a worse current source than the ones you built in previous chapters 6 2 2 Differential amplifier with current source loads Various tricks can be used to improve the performance of the current mirror as we will see below But first hook up your simple current mirror to your three transistor differential amplifier replacing the 10 k collector resistors and remove the 100 Q emitter resistors see Fig 6 4 Connect a scope probe to the collector of Q2 If the inputs balance the currents through Q and Q will be equal and so will the currents through Q4 and Qs But if a differential signal is present
2. cos cos t C 15 wC wC Eq C 15 states that a constant is equal to the same constant times a function of time This can be satisfied for all times only if the constant is zero thus 1 tan a 0 an IRC C 16 Eq C 14 can be simplified as I Vo R cos sing C 17 wC 1 Otherwise we could divide through by the constant to obtain cos wt 1 which clearly does not describe the behavior of the circuit 193 Appendix C RC circuits frequency domain analysis v t Fig 1 Series RC circuit l I R cos b sin 0 aC o Fig 2 Right triangle represented by Eq C 17 illustrating that Vp Io R cos lo g oc sing This describes a right triangle with hypoteneuse of length Vo and sides of length J R and Ip wC Fig C 2 which is a useful way of visualizing the relationship among the amplitudes of the source voltage resistor voltage and capacitor voltage The relationship is Pythagorean hb Vo J R 4 We thus have Ve Io R ze If we take the output as the resistor voltage we get a high pass filter Vo Vout IoR en ey 1 se If we take the output as the capacitor voltage we get a low pass filter Io Vo Vout oC RCY 1 C 18 C 19 C 20 C21 Appendix D Pinouts 741 or 411 op amp P A R 7400 Quad NAND 7404 Hex INVERTER 7432 Quad OR 7486 Quad XOR 7474 D Type 10 Fli
3. 13 2 Tracking ADC To measure an analog signal you need to invert the process of D A conver sion There are various ways of doing this but just as division is harder and slower than multiplication and taking the square root harder and slower than squaring analog to digital conversion is harder and often slower than digital to analog Given a DAC a counter and a comparator a simple approach is to increment the counter starting from zero until the DAC output crosses the analog input Using the comparator to compare the analog input to the DAC output you stop counting when the comparator output switches states At that point the counter holds a digital approximation to the magnitude of the input A simple variant of this circuit will follow or track changes in the input voltage You can turn your 4 bit counter DAC into such a tracking ADC by driving U D from a comparator that compares the DAC output with the analog input voltage Use a potentiometer to make the analog input voltage connect one end to ground and the other to 15 V The slider controls the input volt age which you can vary between 0 V and 15 V To stabilize the op eration of the circuit use some hysteresis by connecting a series 10 k resistor between the input voltage and the comparator noninverting in put and 1 M between the comparator output and the noninverting input see Fig 13 2 gt Clock the counter at a few hertz and observe its state with the T
4. For P type material electrons from neighboring atoms can jump into the holes moving the holes from one place to another The holes can migrate in the direction of an electric field The charge motion is thus due to the motion of the holes i e P type material has positive charge carriers If a junction between P type and N type semiconductor material is cre ated within a single crystal in such a way that the crystalline structure is preserved across the junction the result is a junction diode Electrons from the N region migrate across the junction into the P region filling holes as they go This creates a net charge build up around the junction see Fig 3 1 positive in the N region and negative in the P region leading to an internal electric field as shown Once the holes are filled the junction region becomes devoid of charge carriers and thus acts as an insulator preventing further current flow If an external field is applied in the same direction as the internal field the depletion region region around the junction devoid of charge carriers increases in size so current does not flow On the other hand if an external field is applied opposite to the internal field free charge carriers flow toward the junction Electrons flow into the N type material from the metal contact 33 3 Diodes Internal Electric Field o Hole Free Electron Silicon Germanium Boron Aluminum Q Arsenic Phospho
5. In many freshman physics textbooks the frequency domain analysis of RC circuits is not explicitly treated however it is not particularly difficult Here is a detailed derivation At any moment of time the charge Q stored on the capacitor is proportional to the voltage Vc across it Q CVe C 1 If the voltage across the capacitor is varying sinusoidally in time it follows that the charge must also vary sinusoidally Then since the current J flowing onto one plate of the capacitor is the time derivative of the stored charge the current must also be a sinusoidal function but out of phase with the voltage by 90 since the derivative of the sine is the cosine which is out of phase with the sine by 90 and the derivative of the cosine is minus the sine Now consider a series RC circuit being driven by a sinusoidal AC voltage source Fig C 1 Since the resistor and capacitor are in series they must have the same current flowing through them however it is not necessarily in phase with the source voltage V Suppose for the sake of definiteness that V Vosinat C 2 i e we have chosen the zero of time to be a moment when the voltage across the source is zero Then allowing for an unknown phase difference between the current in the circuit and the voltage applied by the source we can write I hsin t C 3 Kirchhoff s voltage law tells us that at any moment of time the applied voltage must equal the sum
6. Daniel M Kaplan and Christopher 6 White lt OMG ST more information www cambridge org 9780521815369 This page intentionally left blank Hands On Electronics Packed full of real circuits to build and test Hands On Electronics is a unique introduction to analog and digital electronics theory and practice Ideal both as a college textbook and for self study the friendly style clear illustrations and construction details included in the book encourage rapid and effective learning of analog and digital circuit design theory All the major topics for a typical one semester course are covered including RC circuits diodes transistors op amps oscillators digital logic counters D A converters and more There are also chapters explaining how to use the equipment needed for the examples oscilloscope multimeter and breadboard together with pinout diagrams for all the key components referred to in the book Hands On Electronics A One Semester Course for Class Instruction or Self Study Daniel M Kaplan and Christopher G White Illinois Institute of Technology CAMBRIDGE 9 UNIVERSITY PRESS a CAMBRIDGE UNIVERSITY PRESS Cambridge New York Melbourne Madrid Cape Town Singapore S o Paulo Cambridge University Press The Edinburgh Building Cambridge csB2 2Rvu United Kingdom Published in the United States of America by Cambridge University Press New York www cambridge org Inf
7. b ih ril Fig 4 1 a Construction and b circuit symbols and biasing examples for NPN and PNP junction transistors The region common to the two junctions called the base may be of either N type or P type material This thin region is surrounded by material of the opposite type in regions known as the emitter and collector Wire leads are attached to the three regions The circuit symbols for NPN and PNP junction transistors are shown in Fig 4 1 b Note that in the circuit symbol the arrow on the emitter lead points in the direction of positive current flow You can tell whether a tran sistor in a schematic diagram is PNP or NPN by the direction of the arrow The simplest way to think of transistor action is as current amplifica tion a small current flowing into the base controls a large current flowing into the collector Both the base and collector currents flow out from the emitter This description assumes an NPN transistor For PNP the current directions are opposite a small current flowing out from the base controls a large current flowing out from the collector with both currents flowing in through the emitter The ratio of collector current to base current is called B or hfe and is typically in the range 20 to 300 More precisely however a transistor is a voltage controlled current source small changes in the base voltage cause large changes in collec tor current Such a device in which an input voltage cont
8. bers next to each input and output that you use These should be logic diagrams i e gate symbols arranged in a logical order according to their function like the schematics in the following chapters not chip level diagrams such as in Fig 10 2 gt Drive each circuit using two switches on your breadboard and verify that it gives the desired output for each of the four possible input states Record the truth table for each logic circuit Sometimes it is useful to have a gate that outputs a true if one or the other input is true but not both Such a gate is called an exclusive OR XOR gate In Boolean algebra the exclusive OR of A and B is denoted by A B As we shall see below an XOR can be used to test two numbers for equality it also can be used to produce the sum bit for a 1 bit binary addition gt Construct an XOR circuit out of NANDs It should turn on an LED indicator when either input is high but not when both are It is easy to see how to do this with five gates it can also be done with only four Be sure to show both using Boolean algebra and using truth tables for the intermediate signals in your circuit that indeed you have implemented an exclusive OR gt Show how to use an XOR to test two signals for equality Try it out and show that it works displaying the XOR output with an LED logic indicator Does the LED light for equality or for inequality Why 10 3 5 TTL quad XOR gate Use TTL chips for this exerci
9. plitude about 1 V so as not to apply too large a reverse voltage to the capacitor and use a high enough frequency so that the capacitor causes negligible attenuation about 10 kHz Note that polarized capacitors can be safely reverse voltaged by a volt or two r m s but typically not by more than 15 of their voltage rating gt How do your measured impedances compare with what you expect The input impedance should equal times the emitter resistor and the output impedance should equal the dynamic resistance of the emitter as described in section 4 1 3 4 2 3 Common emitter amplifier The common emitter amplifier is a very common transistor amplifier con figuration but that is not how it gets its name the name reflects the idea that the emitter is in common between the input circuit and the output circuit Construct the common emitter amplifier shown in Fig 4 7 gt Predict and measure the quiescent DC voltages i e the voltages when no input signal is present at the base emitter and collector The predictions are easy 1 Apply Ohm s law to the base bias resistive voltage divider to determine the quiescent base voltage Vg Vec R2 R R2 This is an approx imation since it neglects the base current but as you ll see given the large value of the base current is small enough that the approximation is a good one Voc 15 V R 100k R Ro 10k Ro 10k Vout Re 1k 2N3904 Fig 4 7 Commo
10. s 25 mA output current limit Remove the 100 Q load and switch to a 10 kHz square wave as the input Compare the appearance of the output signal and the input signal For sufficiently large amplitude you are likely to observe that the lead ing and trailing edges of the output square wave are not quite vertical gt Measure the slope of the leading edge in volts per microsecond This is the slew rate of the 741C According to the manufacturer the typical slew rate is 0 5 V ws There exist more expensive op amps with much higher slew rates 93 7 Introduction to op amps el Vout Fig 7 5 Circuit for demonstrating a summing junction Since the inverting input is held near ground due to feedback Vouw i In R3 where J1 Vin R and h Vo R2 If Ri Ro R3 Vou Vin Vo The inverting input is called a virtual ground because it is kept at zero volts by feedback Thus even though the open loop input impedance of the inverting input is very large it acts here like a short circuit to the noninverting input ground Since the input signal sees R to ground the input impedance of the inverting amplifier is equal to the value of R4 Note that the virtual ground at the inverting input can also be used as a summing junction all currents arriving at that point are summed and passed through the feedback resistor to the output To demonstrate this feed an adjustable current into the summing junction by adding a 10
11. 3 dB points fy and f of the frequency response If you adjust the output voltage to be 14 1 V peak to peak at f fo you can easily find the 3 dB points by varying the frequency until the output voltage is 10 0 V peak to peak Measure and graph the gain vs frequency for a reasonable frequency range Vout Fig 9 9 Active bandpass filter 124 Hands on electronics Compare fo with the theoretical value 1 2 P sey Riko 9 6 and compare the voltage gain at the center frequency with the theoretical value 1 R2 Ap 9 7 0 IR 9 7 The quality factor for a bandpass filter is fo Q 9 8 fu f Thus a narrow passband corresponds to high Q and a broad passband to low Q Compare your observed Q to the theoretical value for this filter Q T 9 9 Try to explain how the circuit works eee 10 Combinational logic In this chapter you will be introduced to digital logic You will build some logic circuits out of discrete components and some out of integrated cir cuits and familiarize yourself with the 7400 series of CMOS comple mentary metal oxide semiconductor and TTL transistor transistor logic integrated circuits and their basic operation Note The kinds of things one thinks about in digital logic are almost completely different from those in analog electronics Apparatus required Breadboard oscilloscope multimeter 100 Q 330 Q 1 k 2 2 k and 3 3 k 1 W resistors
12. IC op amps have even higher gain than this of course as well as higher input impedance Higher input impedance can be achieved by using Darlington transistor pairs in place of the input transistors or by using FET inputs instead of bipolar transistors The gain can be increased fur ther by adding a second stage of amplification after the differential pair To achieve low output impedance the output is usually buffered with an additional transistor stage 7 Introduction to operational amplifiers An operational amplifier is a high gain DC coupled amplifier with differ ential inputs and single ended output Op amps were originally developed as vacuum tube circuits to be used for analog computation Nowadays they are packaged as integrated circuits ICs Such devices can closely approxi mate the behavior of an ideal amplifier and their use avoids the necessity of coping with the messy internal details of amplifier circuitry Thus an IC op amp is often the device of choice in scientific instrumentation In this chapter we will introduce the op amp and its most common applications Apparatus required Breadboard oscilloscope multimeter two 741 op amps one further 741 optional one 100 Q three 10 k two 100 k one 1 M 1 W resistors and four more 10 k resistors optional 7 1 The 741 operational amplifier 85 The IC we shall be using is a general purpose op amp designated by the number 741 The 741 is a very popular and succe
13. and see if you are right if not fix it Record the truth table for this function 12 3 4 RAM A random access memory RAM is a chip containing a large number of flip flops each designated by a unique numeric address Each flip flop can 163 12 Monostables counters multiplexers and RAM BA 5 pin24 GND pin12 5 pin 16 GND pin 8 Fig 12 7 Pinout of 7489 16x4 RAM be accessed by address for reading or writing Frequently the flip flops are organized into multi bit words with each word separately addressable For example the 7489 Fig 12 7 74189 and 74219 are pin compatible 64 bit RAM chips organized as sixteen words of 4 bits each Each has four address bits labeled A through D for selecting words 0 15 four data inputs DI through DI for writing a value into the word being addressed and four data outputs DO through DO for reading the word being ad dressed Of course 64 bits in a chip is nothing nowadays but it serves conveniently to illustrate the random access memory principle using a relatively simple chip 164 Hands on electronics To write a 4 bit word into the memory WE write enable is brought low This causes the state of the inputs to be recorded in the word being addressed When WE is high the word being addressed is read nondestruc tively Regardless of the state of WE the word being addressed appears at the output When the address bits change the outputs settle to their new
14. assorted resistors and capacitors The circuits in this lab are rather involved and many of the details of their design are left for you to work out You will need to work them out in advance if you are to have any hope of completing the exercises in a timely fashion 156 Hands on electronics e 12 1 Multivibrators Multivibrator circuits fall into three general categories e Astable These circuits have no stable state but keep changing from one state to the other hence the name multivibrator They are very useful as clocks or oscillators You used a 555 as an astable multivibrator in chapter 9 Bistable These circuits can be induced to go from one state to another and can remain in either state permanently after the input signals have been removed They are thus stable in both of their allowed states The more common term for bistable multivibrator is flip flop Monostable These circuits have only a single stable state They can be forced out of their stable state by a trigger pulse but they return to it after a very limited period of time The primary use for monostables is to create pulses of known duration from triggering pulses of shorter longer or variable duration Monostables are widely used to generate gate signals for counter circuits They are considered to be hybrid analog digital chips in that the digital output is typically determined by the RC time constant of an external analog circuit connected to the ch
15. value after a propagation delay called the read access time Since the RAM chip contains sixteen words not ten before hooking it up replace your 7490 decimal counter with a 4 bit binary counter e g the 7493 The 7490 and 7493 are pinout compatible but the 93 counts from 0 15 allowing all sixteen words of memory to be addressed gt Clock the 4 bit binary counter from a debounced push button and verify that it counts through all the hexadecimal base 16 digits from 0 binary 0000 to F binary 1111 Open collector outputs RAM chips are designed for easy multiplexing with a minimum of addi tional components since to increase the total amount of memory available in a circuit one often wants to connect the outputs of multiple RAM chips together In the case of the TTL version of the 7489 this is accomplished by making the data outputs open collector rather than the standard TTL totem pole output circuit This means that the output transistors will not operate properly unless a pull up resistor to 5 is provided for each one Since we are not worrying about speed here any convenient resistor in the range of a few hundred ohms to 10 k is suitable More modern memory chips use three state outputs thus eliminating the need for pull up resistors and also improving the rise time when driving high capacitance The master enable ME signal is provided for use when the outputs of multiple chips are connected together to allo
16. which includes chapter by chapter correspondences to some popular electronics texts written at similar or somewhat deeper levels to ours the two slim volumes by Dennis Barnaal Analog Electronics for Scientific Application and Digital Electronics for Scientific Application reissued by Waveland Press 1989 Horowitz and Hill s comprehensive The Art of Electronics Cambridge University Press 1989 Diefenderfer and Holton s Principles of Electronic Instrumentation Saunders 1994 Introduction and Simpson s Introductory Electronics for Scientists and Engineers 2nd edition Prentice Hall 1987 There is also a glossary of terms and pinout diagrams for transistors and ICs used within The reader is presumed to be familiar with the rudiments of differential and integral calculus as well as with elementary college physics including electricity magnetism and direct and alternating current circuits although these topics are reviewed in the text The order we have chosen for our subject matter begins with the basics resistors Ohm s law simple AC circuits then proceeds towards greater complexity by introducing nonlinear devices diodes then active devices bipolar and field effect transistors We have chosen to discuss transistors before devices made from them operational amplifiers comparators dig ital circuitry so that the student can understand not only how things work but also why There are other texts that put
17. zero volts between the inverting marked in schematics and noninverting marked inputs would yield zero volts at the output relative to ground in other words e the common mode gain and DC offset of an ideal op amp are zero Moreover e the differential gain and input impedance of an ideal op amp are infinite and the output impedance is zero e the bandwidth frequency range over which the op amp can correctly operate and slew rate rate at which the output voltage can change of an ideal op amp are infinite While of course it is impossible to build a circuit having these ideal characteristics one can come remarkably close The above statements are approximately true for practical op amps for example one can buy op amps with gains of 10 to 10 88 Hands on electronics Vout Fig 7 2 Op amp inverting amplifier circuit Note the negative feedback resulting from the resistor that connects the output to the inverting input Op amps are almost always used with negative feedback We shall see next that these approximations lead to a very simple way of analyzing op amp circuits 7 1 3 Gain of inverting and noninverting amplifiers Fig 7 2 shows an op amp configured as an inverting amplifier The key principle at work in this circuit is negative feedback The idea is that a fraction of the output signal is applied at the inverting input Since the gain of the op amp is large and the noninverting
18. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Push Button 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 De Bounced 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Switches 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 wm AN 33333388 Gcrouporasy 8388 piiiiiii 10 k pot 1k pot Q0U0U0U0 Logic Switch Bank SPDT Switches Fig 1 1 Illustration showing many of the basic features of the PB 503 powered Protoboard with internal connections shown for clarity Note that each vertical column is broken into halves with no built in connection between the top and bottom AWG number may damage the socket so that it no longer works reliably for thin wires The PB 503 sockets are internally connected in groups of five horizontal rows or twenty five vertical columns see Fig 1 1 Each power supply connects to a banana jack and also to a row of sockets running along the top edge of the unit The three supplies 5 V red jack 15 V yellow jack an
19. 10 12 11 12 D3 D4 8 07 8 16 17 13 12 12 13 D5 8 14 8 18 26 8 34 13 13 14 D6 4 16 9 15 16 9 20 15 Key D amp H A James Diefenderfer and Brian E Holton Principles of Electronic Instrumen tation Saunders 1994 Barnaal Dennis Barnaal Analog Electronics for Scientific Application and Digital Electronics for Scientific Application reissued by Waveland Press 1989 H amp H Paul Horowitz and Winfield Hill The Art of Electronics 2nd edition Cambridge University Press 1989 Simpson Robert E Simpson Introductory Electronics for Scientists and Engineers 2nd edition Prentice Hall 1987 Appendix A Equipment and supplies General equipment you will need one Global Specialties PB 503 powered breadboard or equivalent one Tektronix TDS 210 Dual Trace Oscilloscope or similar two oscilloscope probes with 10X attenuation one digital multimeter with probes one power tranformer 12 6 V each side of center tap four 50 100 cm banana leads two red and two black Analog components 185 Resistors A WwW Number required Capacitors Number required 33 Q 1 50 pF 1 68 Q 1 100 pF 1 100 2 3 300 pF 1 330 Q 2 0 0047 uF 1 560 2 1 0 01 pF 1 820 Q 1 0 033 pF 3 1kQ 2 0 1 pF 1 2 2 kQ 1 0 47 pF 1 3 3 kQ 3 1 pF 1 4 1 KQ 3 100 pF 1 10 kQ 7 1000 pF 1 22 kQ 2 100 kQ 2 330 kQ 1 1 M2 1 10 MQ 1 1 KQ 1 a2 W resistor 250 V capacitor 186 Hands on electronics eS Diodes transistors a
20. 43 RS latch 145 153 sample and hold 177 saturated switch 60 saturation bipolar transistor 59 60 transistor 68 saturation current 33 52 saturation drain current FET 68 saturation region FET 67 saturation voltage 91 Schmitt trigger 116 search algorithm binary 171 logarithmic 171 sequential logic 143 series 5 6 8 SHA 177 shift register 181 short circuit 7 11 shunt resistor 104 signal processing op amp 101 simple transistor model 51 sine cosine oscillator 122 slew rate 87 source follower 71 SPDT switch 152 speed transition 126 state internal 143 146 149 162 state diagram 143 state machine 143 162 state table 146 static resistance 37 stored charge 61 stray capacitance 115 successive approximation ADC 171 summing junction 93 169 switch 152 momentary contact 153 SPDT 152 level breadboard 137 138 switch debouncer 153 synchronous counter 152 157 synchronous logic 144 table state 146 table truth 140 141 143 146 tester equality 141 theorem DeMorgan s 141 146 Th venin equivalent circuit 45 three state output 164 three terminal voltage regulators 45 threshold voltage 113 TIL311 display 158 time constant 24 time domain 15 102 timer 118 156 555 timing diagram 143 timing network RC 159 TO 92 case 54 toggling flip flop 148 totem pole output 133 164 tracking ADC 170 transconductance amplifier 48 transconductance FET 68 transis
21. 9 6 9 7 9 8 9 9 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 11 List of figures Basic op amp differentiator Improved op amp differentiator Basic op amp integrator Improved op amp integrator Op amp logarithmic amplifier Op amp exponential amplifier Simple and improved versions of an op amp half wave rectifier Op amp follower with push pull output buffer power driver with two feedback arrangements Block diagram showing how to build an exponentiator Poor comparator and 311 comparator 311 comparator with 10 k series input resistor Schmitt trigger using 311 comparator RC relaxation oscillator using comparator Block diagram for the 555 timer IC 555 timer IC used as an oscillator and as a one shot or timer 555 timer configured as an alarm Sine cosine oscillator Active bandpass filter Logic levels for various 7400 family lines Labeling of 7400 series chips Standard logic gates with truth tables De Morgan s theorems expressed symbolically Two input diode gate Diode transistor NAND gate using 2N3904s Schematic representation of an enhancement mode N channel MOSFET Schematic representations of a CMOS inverter constructed using one N channel and one P channel MOSFET Schematic representation of a CMOS NAND gate with LED logic level indicator Logic level switch using either an SPST or SPDT switch and a pull up resistor Circuits for measuring the channel r
22. ADC0804 or similar 7400 7432 four 7474 74112 74138 168 Hands on electronics EE 13 1 A simple D A converter fabricated from familiar chips Recall that when an op amp is set up as an inverting amplifier the non inverting input is grounded and the inverting input which is tied to the output through a feedback resistor acts as a virtual ground If a resistor R is connected from a voltage V to the inverting input of the op amp a current V R will flow If you double the resistance half as much current will flow Suppose you have four resistors with the resistances R 2R 4R and 8R The corresponding current flows will be in the proportion 8 4 2 1 see Fig 13 1 a A 74191 counter has four outputs Q through Qo with Q the MSB most significant bit and Qo the LSB least significant In addition it has four parallel load inputs count enable and count direction up down inputs and ripple clock and terminal count outputs for use when cascading multiple stages If we feed the counter outputs to the inverting input of an op amp through resistors R 2R 4R and 8R in order from MSB to LSB we get a 4 bit digital to analog converter The current into the feedback resistor will be proportional to the number that corresponds to the state of the counter Given a suitable feedback resistor such that the op amp does not saturate the output voltage will be proportional to this current To produce a desired output voltage we can load
23. Chapter 11 A positive signal at SET causes Q to be near ground while a positive signal at RESET causes Q to be high A high value for Q turns on the transistor switch which drives the DISCHARGE pin toward ground The output stage is an inverting buffer so SET causes the output to go high while RESET causes the output to go low Begin by connecting a 555 as shown in Fig 9 6 a and observe the output When the output is high the capacitor is charging through Ra and Rg When the capacitor voltage Vc exceeds Vcc the DISCHARGE pin is driven toward ground and the capacitor discharges across Rg The cycle repeats once Vc falls below Vec The frequency is predicted as 1 FO 2Rpg C 22 f 120 10k Hands on electronics Vec Discharge Reset 555 Fig 9 6 a 555 timer IC used as an oscillator b 555 timer IC used as a one shot or timer gt Sketch the output waveform and briefly explain the operation of this circuit Is the output symmetric If not why not gt Derive Eq 9 3 and compare the measured output frequency with the predicted oscillation frequency gt Examine the voltage Vc across the capacitor Record its minimum and maximum values Do they make sense gt Try replacing Rg with a short circuit what happens Explain why Put Rpg back for the next part gt Try changing V to 5 V and observe how the output changes To what extent does the output frequency depend on supp
24. D while the clock is low or high What happens gt Now check whether the SET and RESET inputs take precedence over the clock and D inputs for example try asserting RESET i e apply a low level to it and see whether you can clock in a high level applied at D gt Disconnect the D input from the logic switch and connect the Q output to the D input to make a toggling flip flop Be sure to deassert SET and RESET What happens now when you apply clocks gt Try clocking the toggling flip flop using a digital square wave from the function generator and use the scope to look at the input and output si multaneously This is sometimes called a divide by two circuit explain what this means gt Measure the flip flop s propagation delay i e the time from the clock transition to the change of output voltage what is it Is it about what you would expect for chips of this family How does it compare with the manufacturer s specifications Be sure to trigger the scope on Q not the clock signal As mentioned above a good technique for precise timing of digital signals is to set both scope channels to 1 or 2 V division and use the scope s vertical position knobs to overlay both grounds below the center of the graticule then you can easily measure the time at which each signal crosses the midpoint between logic low and logic high 1 5 V for TTL and 2 5 V for standard CMOS 11 3 JK flip flop The JK flip flop Fig 11 5
25. Electronics http www newark com Tequipment http www tequipment net Electronix Express http www elexp com Arrow Electronics http www arrow com Jensen http www jensentools com 1 The publisher has used its best endeavors to ensure that all URLs referred to in this book are correct and active at the time of going to press However the publisher has no responsibility for the websites and can make no guarantee that a site will remain live or that the content is or will remain appropriate Appendix B Common abbreviations and circuit symbols Order of magnitude prefixes m milli 10 3 u micro 10 n nano 107 p pico 107 f femto 107 5 k kilo 10 or kilohm 10 Q M mega 10 or megohm 10 Q G giga 10 T tera 10 Mathematical symbols of order 7X approximately equal to equals by definition A change in implies Electrical terms hrg transistor current gain angular frequency Q ohm A ampere AC alternating current C coulomb C capacitance dB decibel DC direct current F farad 188 189 Appendix B Common abbreviations and circuit symbols f frequency gm transconductance H henry Hz hertz I current L inductance P power Q quality factor of a bandpass filter R resistance V volt Vcc most positive voltage in a circuit positive supply voltage Vez most negative vo
26. Schematic representations of a CMOS inverter constructed using one N channel and one P channel MOSFET MOSFETs can thus be combined in parallel to create an inverter as shown in Fig 10 8 A NAND gate can be constructed by adding two more MOSFETs see Fig 10 9 The inverter operates as follows e When the input is high the N channel MOSFET is on and has a low resistance between drain and source while the P channel MOSFET is off and has a high resistance between drain and source The output is thus connected through a low resistance path to ground and goes low e If the input is near ground the P channel MOSFET is on while the N channel MOSFET is off The output now has a low resistance path to Vcc and is pulled high A drawback is that if the input is at an intermediate voltage then both channels are partially open which results in current flowing through both FETs from power to ground While CMOS logic draws very little power when in a steady state i e all signals either high or low it thus draws much more power when signals are switching between high and low Another drawback of MOSFETs is their sensitivity to static electricity discharge The oxide insulating layer between the gate and the channel is usually quite thin and easily damaged Static charge accumulating on a human in cold dry conditions can easily develop a potential of sev eral thousand volts Although the total energy released is small if this is discharg
27. a Uke Vout Pen nero Fig 3 7 a Power transformer with half wave rectification b waveform produced by circuit shown in a Transformer Rectifier Diode fuse 120 Vac Ripple Voltage B b L s 1 60 Ripple Voltage c PN 60 Fig 3 8 a Half wave rectifier with filter capacitor b waveform produced by circuit shown in a c simple approximation to waveform produced by circuit shown in a 43 3 Diodes gt What is the voltage rating of your capacitor Make sure it is sufficient for the voltage that will be applied gt Observe and record the output voltage waveform across the load resis tance R and measure the peak to peak ripple voltage i e the amount by which the output voltage is varying see Fig 3 8 b Here is that rare situation measuring accurately a small AC signal on top of a large DC offset in which you should use the AC coupling feature of the scope s vertical menu If you are troubled with noise you may want to trigger the scope on line and employ signal averaging A simplified analysis approach for predicting the expected output wave form illustrated in Fig 3 8 c is to assume that the capacitor charges up to the peak voltage instantaneously and discharges at a uniform rate dQ dr equal to the average load current The average current through the load can be determined using the known resistance Ry and the av
28. a wire into the appropriate breadboard socket and grabbing the other end of the wire with the scope probe s grabber The function generator s amplitude and frequency are adjusted by means of sliders and slide switches gt Look at each of the waveforms available from the function generator square sine and triangle Try out the frequency and voltage controls and explain how they work Adjust the function generator s frequency to about 1 kHz gt Display both scope channels with one channel looking at the output of the function generator and the other looking at the scope s calibrator signal Make sure the vertical sensitivity and offset are adjusted for each channel so that the signal trace is visible gt What do you see on the screen if you trigger on channel 1 On channel 2 gt What do you see if neither channel causes triggering for example if the trigger threshold is set too high or too low gt How does this depend on whether you select normal or auto trigger mode Why If you find this confusing be sure to ask for help or study the oscilloscope manual more carefully 1 3 6 Additional features The TDS210 has many more features than the ones we ve described so far Particularly useful are the digital measurement features Push the MEASURE button to program these You can use them to measure the amplitude period and frequency of a signal The scope does not measure amplitude directly How then can y
29. about 0 7 V Although it has voltage gain Vout Vin of about unity actually slightly less because of the logarithmic dependence of Vgg on Jc implied by Eq 4 3 it is still an amplifier it has high input impedance and low output impedance and can thus provide current gain i e output current gt input current which is what is meant by buffering gt Start by grounding Vin You can determine Ig and Jc within the uncer tainties due to the resistor tolerances by measuring the voltage drops 1 Since power is the product of voltage and current power amplification can occur through an increase in either quantity 56 Hands on electronics across Rp and Rg Derive an approximate value for your transistor by computing the ratio of collector current to base current gt Now drive Vin with a sine wave from the function generator and compare the input and output signals What are the input and output amplitudes If they seem to differ significantly make sure both scope probe com pensations are properly adjusted Measure the DC voltage shift Ver between the base and emitter The 330 Q base resistor is in series with the input resistance rgg Re so it has little effect on the signal It is there to prevent parasitic oscillation which might otherwise occur due to the inductance of the wire jumpers and the parasitic capacitive coupling between the emitter and the base Parasitic refers to capacitance that is there
30. add to the collector current of one transistor and subtract from that of the other transistor so the differential voltage gain should be RL Rg re One half of the amplified differential signal appears at each collector In other words a small differential input voltage applied to the two bases causes a large differential output signal at the two collectors 6 1 3 Measuring the differential gain Wire up the circuit check it against your schematic Fig 6 1 and try it out Because it has a large gain you will need to use a small enough amplitude out of the function generator so that the amplified signal is not clipped cut off at the top or bottom However when the function generator is set to a small amplitude it puts out a rather noisy signal with a relatively large DC offset To avoid these problems run the function generator output through a 100 to 1 attenuator voltage divider made from a 10 k resistor in series with a 100 Q resistor to ground Fig 6 1 b gt Measure the attenuation voltage division ratio by setting the function generator for a large amplitude and measuring the signal amplitudes before and after the voltage divider Compare your observed attenuation with the theoretical value Now that you know the attenuation you can display the function generator output on the scope and calculate from it the size of the actual input signal to the amplifier Connect the output of your attenuator to the base of Q1
31. and observe the amplifier outputs at the collectors of Q and Qo gt Measure the differential voltage gain A gige A Vout Vour ACVin Vin_ for a few different input amplitudes and frequencies compare with what you expect The amplifier circuit clips its output when all of the available current has been switched to one transistor or the other this determines maximum and minimum voltages beyond which the output cannot go gt Try it and see At what output voltages does clipping set in Compare with what you expect you can estimate the amount of current that is available to either transistor by measuring the voltage drop across R 78 Hands on electronics SS 6 1 4 Input offset voltage If you ground both inputs what are the output voltages For an ideal differ ential amplifier they should be equal but you will probably find that due to small mismatches between the two collector resistors the two emitter re sistors and the two transistors they are not To obtain exactly equal outputs you would have to input a small voltage difference called the input offset voltage which you can estimate as the output voltage difference divided by the voltage gain gt How big an input offset voltage do you obtain this way 6 1 5 Common mode gain It is desirable for a differential amplifier to be insensitive to common mode input i e identical signals applied to both inputs This feature called common mode reje
32. approach and one used in many ADC chips is based on the binary or logarithmic search algorithm in which at each step you reduce the search range by half For example if you re looking up a word in an n word dictionary first look at word n 2 If the word you want comes later in the alphabet next try word 3n 4 if your word comes earlier next try n 4 At the next step there are four possibilities word n 8 3n 8 5n 8 or 7n 8 and so on This method will find any word in at most log n steps In the case of analog to digital conversion the logarithmic search has another name successive approximation If there are n output bits there are 2 possible output values but instead of trying each value in succes sion you try each bit in turn starting from the MSB first generate a 1 bit approximation to the value then correct it to 2 bit accuracy then 3 bit and so on 172 Hands on electronics ADC080x The ADCO80x series of chips are inexpensive 8 bit successive approximation A D converters The logic inputs and outputs are compat ible with both TTL and CMOS and the outputs have tri state capability The chips are general purpose ADCs that can be used as stand alone converters or interfaced with a computer or other logic system They accept differential inputs for increased common mode noise rejection capability The digitized output thus measures the voltage difference Ving Vin_ The successive approximation algorithm used
33. are manufactured with controlled reverse breakdown prop erties Their forward characteristics are similar to those of junction diodes however Zener diodes are used in reverse biased mode While reverse breakdown typically destroys a standard junction diode Zener diodes are designed to operate at and around their reverse breakdown Zener voltage The Zener voltage is determined during the manufacturing process by ad justing the semiconductor doping Typical Zener voltages range from 3 3 to 75 volts Schottky diodes are manufactured by bonding a metal conductor to an N type semiconductor Electrons from the N type material migrate into the metal This migration creates a potential barrier across the boundary which then behaves in a similar fashion to a PN junction In general Schottky diodes are used in applications requiring high speed and low capacitance Physically most diodes look like a little cylinder with wires sticking out the two ends Fig 3 4 To distinguish the ends from each other the manufacturer often prints the diode circuit symbol on the diode body Alternatively sometimes a ring is marked around the body close to the cathode the N type end to distinguish it from the anode the P type end Diodes are manufactured with specified values for maximum current forward voltage drop leakage current reverse saturation current reverse breakdown voltage and switching speed time required for the diode to e
34. at one tenth the frequency of the input clock gt First figure out how to configure a 7490 as a divide by ten clock it with a digital square wave and verify that the output is indeed a symmetrical i e high half the time and low half the time square wave at one tenth the input frequency Write down the state table and sketch the timing diagram for the four output bits with respect to the clock input Also don t forget to write down your complete schematic with pin numbers gt Next configure your 7490 as a decimal counter so that as successive clock pulses are applied it sequences through the states 0 9 in order 0000 0001 0010 1001 gt Display the state of the counter with a TIL311 hexadecimal LED display Fig 12 2 as explained in the following paragraphs TIL311 numeric display The TIL311 is a handy but expensive hexadecimal display that combines in a single package 22 LEDs each with its own driver circuit a latch that can store the four input bits and a decoder that decides which LEDs to turn on for a given input state Note that unlike most chips the TIL311 has three notches on its package rather than one as indicated in Fig 12 2 Also pins 6 9 and 11 are missing The data sheet can be obtained from the Texas Instruments website Although the TIL311 is a TTL device it 1 http Awww ti com 159 12 Monostables counters multiplexers and RAM will display correctly the output of aCMOS chip
35. both N and P channel MOSFETs vary the gate voltage between 0 and 5 V and measure the channel resistance as a function of gate voltage Note if you try to measure the resistance directly with the meter you Vec 5V Vec 5V ia channel Ci p MOSFET A ri G N channel Vin MOSFET s dG iw Fig 10 11 Circuits for measuring the channel resistance as a function of gate voltage 139 10 Combinational logic will fail since the quiescent current flowing in the channel will confuse the ohmmeter Measure the output voltage and infer the resistance using the voltage divider equation gt On a single graph plot the channel resistance for both the N and P channel MOSFETs vs gate voltage Comment on your results As discussed above the complementary nature of P and N channel MOSFETs which you ve just demonstrated can be used to create logic gates gt Build the gate shown in Fig 10 8 and determine its function You can easily display the output using an LED indicator If you use discrete components don t forget the current limiting resistor about 330 2 connect the LED and resistor in series between the CMOS output and ground In either case if the LED is on the output is high and if the LED is off the output is low gt Apply CMOS logic levels to the input and note the output Make a truth table and verify that the gate inverts the logic level of the input gt The TTL output of the function generator puts ou
36. can be analyzed as follows e If either input is near ground transistors Q and Q will be off Q2 will consequently be on saturated which causes the output T to be about two diode drops below Vcc e On the other hand if both inputs become high Q s base voltage in creases causing Q to turn on which turns on Q3 Q s base voltage 133 10 Combinational logic drops turning Q2 off Since Q3 is then in saturation the output T is close to ground Assuming the positive logic convention the output voltage thus represents the logic NAND of the inputs The output structure is commonly referred to fancifully as a totem pole output since it consists of a group of stacked components Several im provements have been made since the original introduction of TTL logic resulting in numerous family lines Many are listed in Table 10 1 Quirks of TTL inputs and outputs The gate circuit of Fig 10 6 illustrates some peculiarities of TTL inputs and outputs In general TTL outputs cannot be relied upon to source even small amounts of current however they can sink tens of milliamperes of current Note how the LED logic indicator has been constructed to take advantage of this the LED is lit when the output is low Note also that TTL inputs source current while held low but sink negligible amounts of current while held high The input and output current specifications vary among the different family lines Refer to the
37. comparator Begin by wiring up a 741 in open loop mode as you did in a previous lab Fig 9 1 a With no negative feedback the saturated output that results allows the op amp to be used as a voltage comparator a circuit that tells you whether an input voltage is higher or lower than a threshold voltage the threshold is ground in this case Since op amps are not specifically engineered for open loop operation it is not a very good voltage compara tor in ways that we shall soon see but in some situations when high speed response and high sensitivity are not required an open loop 741 comparator is perfectly adequate gt Start by applying a 1 kHz sine wave to the input and observe what the circuit is doing 113 114 Hands on electronics b Ea 15 15 Fig 9 1 a Poor comparator 741 op amp used in open loop mode b 311 comparator Pinouts shown for eight pin mini DIP package gt Now raise the input frquency to 100 kHz Notice that the output square wave is not very square Try an LF411 op amp in place of the 741 gt For each case studied sketch the output waveform and measure the output amplitude and DC offset Explain your measurements gt Contrast the performance of the LF411 and 741 when configured as com parators What op amp limitation is responsible for the poor comparator performance at high frequency Now substitute a 311 comparator for the op amp The pinouts are NOT
38. constant current independent of its voltage You can verify this using the circuit of Fig 4 8 using a second meter or the scope to make various voltage measurements Start with the load resistance 10 k pot as always be careful to connect it properly so as not to burn it out set to 0 Q gt How much collector current should flow Is this confirmed by your measurement of the emitter voltage Slowly increase the load resistance until the output current starts to decrease At the pot setting where the current source starts to fail output current starts to vary rapidly with load resistance measure the collector voltage What is the compliance of your current source the range of output voltage over which the current is approximately constant Where the current source starts to fail how does the collector voltage compare with the base voltage You should be observing transistor sat uration when Vce lt Vsel the current source behavior stops since 60 Hands on electronics 5 Red LED 330 10k d ee 2N3904 Fig 4 9 Transistor switch the collector base junction becomes forward biased and its impedance decreases Another way of thinking about the same phenomenon is that when the transistor saturates 6 decreases sharply thus the base current increases as the base steals current from the collector gt By measuring the voltage drop across the base resistor take a few mea surements of 6 as you turn up the
39. creates a one input gate an inverter Thus if the output of a NAND is connected to both inputs of a second NAND the result is equivalent to an AND gate 10 1 4 Summary of Boolean algebra Logic operations are best described using Boolean algebra While a detailed exposition of Boolean algebra is beyond the scope of this text we give here a brief introduction and mention a few useful points Consider two logical variables A and B which can take on the values true and false We can then denote logic operations as follows e the logical AND of A and B is denoted as A B the logical OR of A and B is denoted as A B the logical XOR of A and B is denoted as A B e the inverse of A is A and the inverse of B is B the logical NAND of A and B is denoted as A B the logical NOR of A and B is denoted as A B As in any algebra the rules of Boolean algebra allow theorems to be derived starting from axioms An alternative way to prove a theorem in 131 10 Combinational logic a w A H H L L Iriryw C rr rio A L L H H Fig 10 4 DeMorgan s theorems expressed symbolically AET Rees aes 2 Boolean algebra is by exhaustive demonstration i e to write down the truth table for every possible input state work out the value of the output and write it down Two relationships known as DeMorgan s theorems are particularly useful A B A B 10 1 and A B A B 10 2 These are illustrate
40. current flow between drain and source When the channel is open the drain source resistance is quite small 10 100 2 while the drain source resistance is large of order megohms when the channel is closed The MOSFET thus acts like a switch Notice that to turn on an N channel MOSFET the gate voltage is brought positive with respect to the source For a JFET this would result in a large current flowing through the gate to the source since the gate source junction would act as a forward biased diode This does not occur in MOSFETs since the gate and channel are separated by a layer of insu lating oxide The oxide layer allows the electric field to penetrate without allowing current to pass The input impedance for MOSFETs is conse quently even greater than for JFETs Also notice that unlike JFET opera tion the drain source channel is normally closed A positive gate voltage of a few to several volts is required to open the channel and allow current to flow For P channel MOSFETs the voltage relationships are reversed the channel is open when the gate source voltage is negative and closed when the gate source voltage is near zero or positive Combining an N channel and P channel MOSFET gives a comple mentary pair of switches that open and close opposite each other Two 135 10 Combinational logic a Vec Voc Vec S 5 MOSFET P channel Switch 1 MOSFET D Vin Vout Vout Vout D G N channel MOSFET MOSFET Switch 2 Fig 10 8
41. elaborate mathematical operations on voltages For example the square of a number can be found by taking the logarithm of the number multiplying by two and then taking the antilogarithm of the result see Fig 8 10 similarly the product of two numbers equals the antilog of the sum of their logarithms x log 2 log x 8 16 x x y log logx log y 8 17 Choose an arithmetic function of your choice other than addition sub traction and multiplication by a constant and design a circuit using op amps to perform that function Make a plot of the output vs input voltages to verify that the circuit works correctly Discuss the limitations of your circuit Comparators and oscillators i In this chapter you will encounter some applications of positive feedback in op amp and comparator circuits You will see how uncontrolled feed back can cause unwanted oscillation and how controlled positive feedback hysteresis can be used to eliminate unwanted oscillation or produce in tentional oscillation There is also an optional active filter application at the end Apparatus required Breadboard dual trace oscilloscope with two attenuating probes two 741 and one LF411 op amp 311 comparator 555 timer one 100 Q one 820 Q two 1 k two 3 3 k three 10 k one 100 k one 1 M and one 10 M 1 W resistor three 0 033 uF one 0 01 uF and one 1 pF capacitor one red LED and two 3 3 V Zener diodes 9 1 Experiments 9 1 1 Op amp as
42. forward current flow It would offer infinite resistance when reverse biased i e no current would flow regardless of the size of the applied reverse voltage You can see from Fig 3 3 that real diodes typically approximate the ideal reasonably well with only a few hundred millivolts of forward voltage over a wide range of forward current and with reverse current measured in nanoamps even for volts of reverse voltage as long as the reverse voltage is kept small enough to avoid breakdown For the typical range of currents encountered in most electronic circuits a few to hundreds of milliamps a 37 3 Diodes handy approximation is that a forward biased germanium diode has about a 300 mV voltage drop across it while a forward biased silicon diode has about a 600 mV drop 3 4 Diode action a more sophisticated view If we want we can think of a diode as a resistor whose resistance depends on the current flowing through it i e the resistance is dynamic rather than having a constant or static value While the static resistance of a device is the voltage across the device divided by the current through it R V I Ohm s law the dynamic resistance is the slope dV d of the V curve at any point You can see that for a resistor the static and dynamic resistances are the same but for a device whose V I curve is nonlinear they become different Note in particular that a nonlinear device does not have a static resistance
43. guaranteed to be destroyed if by mistake you power them backwards They may also be destroyed if you apply a voltage higher than 7 V to any pin 5 5 V for the original 7400 TTL family 10 3 Experiments 10 3 1 LED logic indicators and level switches The PB 503 breadboard has eight built in LED indicators These are in tended for use as logic level displays A high level applied to the input will light the LED try connecting one to ground or 5 V and see that it works If you ever find a need for more than eight indicators you can augment the built in indicators with individual LEDs in series with several hundred ohm current limiting resistors this is also a good solution if your breadboard lacks built in logic indicators gt Drive an LED logic indicator with a variable voltage between 0 and 5 V Explore the threshold voltage and compare with the CMOS and TTL logic levels Two single pole double throw SPDT switches are available at the lower right hand side of the PB 503 The PB 503 also provides a bank of eight level switches in a unit located near the lower left corner These can be used as logic level switches as shown in Fig 10 10 The switches make a connection either to power or to ground The power voltage depends on the setting of a master switch located to the right of the eight switch unit and allows for flexibility when working with low voltage CMOS ICs or other nonstandard ICs Older versions of the
44. highest numbered pin is at the upper left Almost always when you orient the chip this way the writing on the top will be right side up see Fig 10 2 10 1 3 Logic gates There are six basic logic gates as shown in Fig 10 3 These gates are sufficient to implement all logic functions although the more complex functions are also available as specialized chips multiplexers decoders etc to be discussed later which can simplify design as well as reduce cost Although Fig 10 3 shows only two input gates versions also exist with three four or even eight inputs Note that NAND and NOR are opposites to AND and OR NAND equals not AND while NOR equals not OR Also note that the NAND is a negative logic OR while the NOR is a negative logic AND This follows from DeMorgan s theorem about which more below The small circle shown at the outputs of the NAND and NOR is shorthand for an inverter a NAND is equivalent to an AND followed by an inverter and similarly for NOR 130 Hands on electronics AND OR XOR NOT A Out L H gt Co NAND INVERTER Fig 10 3 Standard logic gates with truth tables After the inverter the NAND is the simplest logic gate to construct from discrete components and historically it was the most commonly used gate NAND is a universal logic function in that the other logic functions can all be created using NAND gates For example connecting together the two inputs of a NAND
45. in these chips requires sixty four clock cycles to complete a conversion A few additional clock cycles are used during startup and after the conversion to latch the data on the output lines The clock can originate from either an external or internal self clocking source The self clocking option uses an on chip oscillator with Schmitt trigger timing input in combination with an external resistor and capacitor that determine the period as shown in Fig 13 3 All of the input and output control signals are active low There are three input control lines labeled Cs RD and WR An A D conversion is started 5 V LSB Internal Clock Osc T Outputs MSB Fig 13 3 a Pinout for the ADC080x series of A D converters b The on chip self clocking configuration Note the locations of the most significant bit MSB and the least significant bit LSB The x in ADC080x means that multiple versions of this IC exist e g ADC0804 173 13 Digital lt gt analog conversion by bringing RD and WR low simultaneously Cs is used in microprocessor based applications for this exercise it should be connected to ground RD is equivalent to output enable RD high puts the outputs into their high impedance state when low the output lines are active therefore connect RD to ground With Cs tied to ground WR simplifies to A D START i e start the digitization now Once the digitization completes the
46. input is grounded any nonzero voltage at the inverting input will cause a large output voltage of the opposite sign If you think about it you will see that the only stable situation that can result is that the voltage difference between the inverting and noninverting inputs is zero In other words the op amp will do whatever is necessary to zero the voltage difference at its inputs Once this principle is grasped it is easy to compute the gain of the op amp inverting amplifier Assuming the input currents of the op amp are zero all the current flowing in through R must flow out through Ro i e h I Assuming that the open loop voltage gain i e that without any feedback of the op amp is infinite the voltage difference at the op amp s inputs must be zero Applying Ohm s law to R and R2 and designating the voltage at the inverting input as V_ V in TR 0 7 1 gt h 1 2 89 7 Introduction to op amps Vou V hR h R2 7 3 R2 gt Vout Vin 7 4 R Thus the closed loop voltage gain i e the gain with feedback of this circuit is Vout _ k Vi Ri Ay 7 5 In a nutshell since all of the current due to the input signal flows around the op amp the output voltage is determined entirely by Ohm s law applied to R and R2 Thus if R 10k a gain of 10 can be achieved by choosing R 100k and a gain of 1 results from choosing R 10k Fig 7 3 shows an op amp configur
47. into the counter any desired value we can also increment or decrement the counter to get a voltage that changes in time in stepwise fashion see Fig 13 1 b This output can of course be observed on an oscilloscope or other measurement device 0 Volts 0000 R R Vy 5V VL 0V Analog Out 9 4 Volts 1111 b Fig 13 1 a Simple D A converter b output waveform resulting from input counting sequence 169 13 Digital lt gt analog conversion To demonstrate D A conversion you will build such a 4 bit DAC To reduce the chances of hooking up the circuit incorrectly gt Begin by setting up a 74191 counter and make sure it is working properly hook up its outputs to a TIL311 display clock it from a debounced switch and verify that it goes through all sixteen states in order Test it counting both up and down you can control which way it counts using the U D input gt Next hook up the counter outputs to the summing junction of the op amp through resistors as described above Use a 2 2 k resistor to connect to Q3 a 4 7 k resistor for Q2 a 10 k resistor for Q and a 22 k resistor for Qo and connect a 3 3 k feedback resistor Connect a 1 kHz digital signal to the clock input of the counter and view the analog output on an oscilloscope Of course if we wanted to produce accurate analog output voltages we would need precision resistors for example 2 50 k 5 0 k 10 k and 20 k Moreover
48. k pot with 10 k resistor in series with the wiper as shown in Fig 7 5 and examine the amplifier output for a small amplitude 1 kHz sinusoidal input gt What happens to the output DC offset as you adjust the pot and why 7 2 3 Noninverting amplifier Set up the noninverting amplifier circuit of Fig 7 3 with R 10k gt With a 1 kHz sinusoidal input measure the gain with R2 100 k and with R2 10k Compare with what you expect Verify that the amplifier is noninverting Leave the 100 k resistor in for the following parts gt Try to measure the input impedance by putting a 1 M resistor in series with the input and looking at the signal before and after the resistor Explain your result The input impedance can be inferred by analyzing the voltage divider cir cuit consisting of the 1 M resistor in series with the input impedance If your answer is 10 M consider that this is the input impedance of the attenuating 94 Hands on electronics scope probe You can get around it by looking only at the output with and without the 1 M input resistor gt What value do you get for Zin this way Again you are seeing the effect of negative feedback even though the open loop input impedance of the noninverting input is only of order megohms itis in principle multiplied by the ratio of the open loop gain to the closed loop gain here a factor of order 10 In practice Zin is limited by other effects such as the capacitan
49. load resistance and the transistor becomes more and more saturated Make a graph of vs Vcr 4 2 5 Transistor switch Transistor saturation is put to good use in the saturated switch Construct the circuit of Fig 4 9 You should see the light emitting diode LED turn on when you connect the input to 5 V and off when you leave it open or connect it to ground If you are unsure which terminal of the LED is the anode and which is the cathode you can check it with a meter or feel free to try it both ways Often the cathode is indicated by a flat spot on the rim of the plastic that encapsulates the diode and some manufacturers make the anode lead slightly longer than the cathode lead Note that the transistor in this common emitter connection is an inverter in the sense that a high voltage level at its input the open end of the series base resistor causes a low voltage level at its output the collector This circuit is called a saturated switch since the transistor goes into saturation Vcge lt Vgel when turned on It has the virtue of dissipating very lit tle power since when the transistor is on the voltage across it is small 61 4 Bipolar transistors whereas when the transistor is off the current through it is essentially Zero gt When the transistor is on what are the base and collector currents You don t need to bother with an ammeter for this measurement just look at the voltage drops across the bas
50. logic design In an asynchronous circuit signals can change at any time requiring the designer to work out in detail the signal propagation delays through all possible paths to make sure that the circuit will work as intended In contrast in asynchronous circuit output signals change only in response to a clock signal Usually there is one common clock for an entire circuit and its transitions low to high or high to low commonly referred to as rising or falling clock edges are used to synchronize all other state changes in the circuit This approach leads to circuits that are easier to design and analyze than asynchronous circuits The synchronous approach is therefore standard in microprocessors for example we have all learned to rate the processing power of computer chips in terms of their clock speed 11 1 4 Timing diagrams Timing diagrams are essential when analyzing synchronous logic circuits As shown in Fig 11 1 timing diagrams for a synchronous circuit usually show the clock signal one or more inputs and one or more outputs Time is shown on the x axis and signal logic levels on the y axis Signal levels 145 11 Flip flops ty hold time OUT tsy setup time 4 tpw pulse width IN tpp propagation delay typ transition time low high CLK trur transition time high low Fig 11 1 Timing diagram with timing definitions for a rising edge triggered flip flop Note that th
51. of bipolar transistors is commercially available of which a small sampling is given here Transistors are commonly rated by their speed e g toggle frequency fr voltage capability maximum current typical hfe and power capability Tomax fr Pig Cost Part Type Application A hye MHz W US 2N3904 NPN _ gen purpose 0 20 100 300 300 0 625 0 06 2N3906 PNP gen l purpose 0 20 100 300 250 0 625 0 06 2N5089 NPN gen purpose 0 05 450 1800 50 0 625 0 14 2N2369 NPN switching 0 2 40 120 500 0 4 1 40 2N5415 PNP power 1 0 30 150 10 0 99 TIP102 NPN pwr Darlington 8 0 1000 2000 80 0 69 MJ10005 NPN pwr Darlington 20 50 600 175 6 90 with holes It is desirable to have as large a ratio of collector current to base current as possible To achieve this in addition to being as thin as possible the base is made of lightly doped material Since the base emitter junction obeys the exponential diode law for cur rent as a function of voltage small changes in the base emitter voltage dif ference have a large effect on the collector current Thus a transistor can be used as an amplifier a device in which a small signal controls a large signal It is worth keeping in mind that is not well controlled in the transistor manufacturing process Although is approximately constant for a given transistor it varies from transistor to transistor even if they are of the same type For examples of the range of variation see Table 4 1 In add
52. of the constructive and destructive interference between two waveforms As stated above difference amplification is usually used to eliminate common mode noise The circuit shown in Fig 7 9 sums two waveforms and then eliminates one using the difference amp One waveform will be from the function generator while the other will be a 60 Hz wave created as in section 7 2 4 If two function generators are available feel free to replace the voltage follower with the output from the second generator First construct the voltage follower and summing amplifiers as shown in Fig 7 9 Set the function generator to a sine wave with a frequency between 59 and 61 Hz Adjust the generator amplitude to match the amplitude of the voltage follower and observe the output of the summing amp The output should be the linear sum of the two input waveforms Have fun with the circuit by changing the amplitude and frequency Observe what happens with either a triangle or square wave input Using the AC line as your trigger source may be useful here Now add the difference amplifier With the function generator amplitude set to zero adjust the potentiometer until the difference amp output has zero amplitude as with the difference amplifier previously built Now in crease the amplitude of your function generator and observe the difference 2 Tf the local supply frequency is not 60 Hz set the function generator frequency to be within 1 Hz of your local val
53. of the voltage across the capacitor and that across the resistor V Vr Ve C 4 Now by Ohm s law Ve IR and we also have Ve Q C 1 C f I dt Substituting these relations into Eq C 4 1 v R fra C 5 C Jit 1 t bR sin t o T f Ip sin wt dt C 6 to where we have made use of Eq C 3 192 Hands on electronics We can easily carry out the integration in Eq C 6 using the substitution u wt giving at d V hRsin ot p 4f sinu du C 7 wC wto o I hR sin at ran wt h cos wto C 8 02 The constant of integration cos wto can be determined by the condition V 0 0 which we assumed in writing Eq C 2 VO 0 bRsing 2 leos cos wf C9 giving cos wtp cos oRC sing C 10 thus V hRsin ot 2 feos ot coso RCsin C11 IpR sin wt sing 2 feos wt cos 4 C 12 which clearly satisfies V 0 0 Eq C 12 can be simplified using the trigonometric identities for sines and cosines of sums V IpR sinwt cos cos wt sing sing I zg eos t cos sin t sing cos C 13 w Gathering and separating terms in sin t and cos t and using V Vo sin t since sin wt and cos t are independent functions of time we obtain two equations I Vo sin wt ue coso ma sin 6 sin wt C 14 w r Ip P Io IoR sing cos IoR sin
54. out signal to the next stage More specifically synchronous counters issue a carry out while for negative edge triggered asynchronous counters the high order output bit from the preceding stage serves to clock the next stage Decimal counters work basically in the same way as binary counters except that they roll over and possibly issue carry out at 9 rather than at 15 this makes them useful for driving decimal displays which are easier for humans to interpret than binary Note that decimal counters are also referred to as decade or BCD binary coded decimal counters Some are actually bi quinary counters i e a divide by five stage coupled to a divide by two 12 3 Experiments 12 3 1 Bi quinary ripple counter The 7490 Fig 12 1 is a negative edge triggered bi quinary ripple counter It advances from one state to the next on the falling edge of its clock input It consists of a 1 bit divide by two stage and a 3 bit divide by five stage that can be cascaded two different ways One way produces a decimal counting sequence 0 through 9 the second produces a divide by ten sequence in 5 pin 5 7490 GND pin 10 Fig 12 1 Pinout of 7490 decade counter 158 Hands on electronics Fig 12 2 Pinout of TIL311 hex display DO D3 are data inputs DPL and DPR connect to LEDs for left and right decimal points LE high latches the input data and BI high blanks the display which the high order bit is a square wave
55. output 3 state see output three state output open collector 164 output three state 164 output totem pole 133 164 output tri state see output three state parasitic capacitance 56 parasitic oscillation 56 passband 124 peak to peak voltage 17 permittivity 16 phase shift 25 pickup 115 pin numbers DIP IC package 129 pinch off 66 pinch off voltage FET 68 pinout 74121 159 74150 162 7489 163 PN junction 32 47 PNP transistor 48 positive feedback 113 positive logic 127 positive edge triggering 147 potentiometer 6 22 23 power supplies 40 powering CMOS ICs 136 powering TTL ICs 136 probe 10 attenuating 10 oscilloscope 10 probe compensation adjustment 10 propagation delay 148 measurement of 148 pull up resistor 114 164 push pull buffer 62 push pull driver 109 203 Index quality factor Q 124 quiescent voltage 57 RAM 162 7489 163 random access memory see RAM RC circuit 15 RC timing network 159 reactance 19 capacitive 19 inductive 19 recording digital 177 rectification 31 36 rectifier 36 40 active 108 full wave 43 half wave 40 ideal 36 op amp 108 reference lead 10 register shift 181 regulator 40 rejection ratio common mode 96 relaxation oscillator 117 resistance dynamic 37 52 57 static 37 resistor pull up 114 164 shunt 104 reverse saturation current 33 52 reverse bias 34 ripple counter 151 157 ripple voltage
56. own words how this circuit works Comment on your observations and measurements 176 Hands on electronics R 100 ka C 100 uF To A D input TAD V Fig 13 5 Method for producing a DC shifted waveform Measuring an AC input signal Replace the DC input with an AC input The most convenient AC input is a waveform from your function generator However the function generator output is symmetric about ground The waveform will thus be outside the ADC range 50 of the time You can DC shift the waveform as shown in Fig 13 5 Warning be careful not to exceed the ADC input voltage range Input voltages larger than Vcc or lower than ground may damage the ADC chip gt Explain how the DC shift occurs and the significance of the component values chosen Suggest at least one other method for DC shifting the input waveform gt Apply a sine wave of 2 V amplitude centered at 2 5 V to the A D input Set the frequency to 0 5 Hz and try to measure the amplitude using the LED indicators You can freeze the A D output using the push button connected to pin 3 Explain how this works gt Compare the input and output waveforms How well do they agree Comment on your observations gt Increase the input frequency you may need to adjust the amplitude to stay within the range of the A D input why What happens to the output waveform as the input frequency approaches the sampling fre quency What happens when the i
57. since V I is not constant We can find the dynamic resistance of a diode by differentiating Eq 3 1 dI ME toy See Le V T 3 4 dV kT thus the dynamic resistance is dV kT e bee eee A 3 5 dI Iet V KT kT aE 6 6 where the approximation is valid for forward biasing such that the 1 in Eq 3 1 is negligible Note that at T 300 K room temperature 1 6 x 107 C 1 ae suy ios 3 7 kT 1 38 x 10 73 J K x 300K 25 mV so the dynamic resistance of a forward biased diode can be simply approx imated by dV 25mvV doo 3 8 These results the exponential dependence of current on voltage and the consequent dynamic resistance formula are important to remember 38 Hands on electronics as they also characterize the behavior of transistors This model of diode behavior neglects some features that matter in practice For example the semiconductor has some ohmic or static resistance that is in series with the junction resistance just described so in practice the dynamic resistance is somewhat larger than that given by Eq 3 8 3 5 Measuring the diode characteristic As before be careful not to burn out your breadboard s 1 k pot hook up the following circuits with the power off and double check each circuit before powering it up gt For the circuit shown in Fig 3 5 estimate the maximum current in your circuit and the maximum power dissipation in the 100 Q resistor is the resisto
58. sure to write down the schematic complete with pin numbers Use a debounced switch to trigger the monostable Clock the two digit counter with the gated clock signal Choose an appropriate input clock frequency for timing the duration of the one shot pulse Calibrate your time scale by using the scope to measure carefully the period of your digital square wave clock input The clock frequency should be low enough that 161 12 Monostables counters multiplexers and RAM the counter does not go past 99 but high enough that the width of the one shot pulse can be measured accurately gt Build the gated counter as described above Include a push button reset that zeros the counter Record the complete circuit diagram including all pin numbers gt Reset the counter and trigger the monostable What pulse width is im plied by the value of the counter and why What clock frequency did you choose and why gt Repeat the measurement about ten times over a period of five minutes in order to determine the reproducibility and stability of the output pulse width Plot your results as a histogram and compute the mean and r m s root mean square duration Save your two digit counter for use in the next section Note on gating clocks When gating a clock with a signal that is independent of the clock e g the push button a standard problem arises If the signal from the push button arrives while a clock pulse is in progress a pulse
59. that n 2 for silicon diodes and n 1 for germanium Thus the output voltage is nkT Vout amp In 8 12 e I nkT x ln Vj In J Rj 8 13 e In practice one should add additional components to compensate for the temperature dependences in Eq 8 13 both the explicit kT factor and the temperature dependence of 7 Often a transistor is used in place of a diode since experimentally one finds that a transistor gives an accurate exponential characteristic over a wider range of current 8 2 Experiments Complete at least the differentiator or integrator exercise the logarithmic or exponential amplifier exercise and the half wave rectifier and push pull driver exercises You should understand the theory of all of the circuits discussed including the ones you choose not to build 8 2 1 Differential and integral amplifiers Differentiator Set up the active differentiator of Fig 8 3 with R 1k Rf 10 k and C 0 033 pF Adjust the peak to peak voltage of the triangle wave input to 10 V and use a frequency in the neighborhood of 500 Hz 107 Integrator 8 More op amp applications gt Measure carefully the peak to peak voltage Vp p and period T of the input signal and from them compute the slope of the input voltage vs time dVin 2V 5 8 14 dt T oo Now look at the function generator output on channel 1 of the scope and the op amp output on channel 2 while triggering on chann
60. the DMM directly across that element see Fig 1 2 Warning This is not true for most AC powered meters and oscilloscopes gt To practice measuring voltages measure and record the voltage between each power supply jack and ground In each case set the meter s range for the highest precision i e one setting above overflow gt Adjust the 15 V and 15 V supplies over their full range and record the minimum and maximum voltage for each Carefully set the 15 V supply to a voltage half way between its minimum and maximum for use in the next part 1 If you wonder what we mean by within reason ask yourself what bad thing would happen if you connected the DMM common to say twenty million volts if you re interested see e g H C Ohanian Physics 2nd edition vol 2 Interlude VI Norton New York 1988 esp pp VI 8 for more information on this 5 1 Equipment familiarization a b Power Supply DMM Multimeter Power Z Supply A mA COM V2 O O Ground o Common uF Fig 1 2 Measuring voltage a An arbitrary circuit diagram is shown as an illustration of how to use a voltmeter Note that the meter measures the voltage drop across both the resistor and capacitor which have identical voltage drops since they are connected in parallel b A drawing of the same circuit showing how the leads for a DMM should be connected when measuring voltage Notice
61. the drain source voltage Vps is sufficiently high This is called the saturation region of the FET characteristic see Fig 5 3 68 Hands on electronics For Vps smaller than a volt or two a JFET behaves like a voltage controlled resistor rather than a current source i e the slope of the I V characteristic is controlled by the gate source voltage This is the linear region of the FET characteristic useful for automatic gain control AGC and modulation applications Don t confuse FET saturation with bipolar transistor saturation they are entirely different phenomena For example recall that bipolar transistor saturation occurs at small Vcg whereas FET saturation occurs at large Vps 5 1 2 Modeling FET action Recall that for bipolar transistors the collector current varies exponentially with the base emitter voltage For FETs operated in the saturation region the relationship is quadratic Ves Ip Ipss 1 tes 5 1 Vp where Vp is the pinch off voltage and Ipss is the saturation drain current for Vos 0 i e gate shorted to source Thus the transconductance is proportional to Ip Em Alp AVgs 5 2 As in the case of bipolar transistors this is only a model and should not be expected to be exact Like the parameter for bipolar transistors Ipss and Vp are temperature dependent and vary substantially even among devices of the same type so good designs minimize the dependence of circuit performa
62. the drain voltage to 10 V ground the source and apply a variable negative voltage to the gate This can be accomplished using either the 1 k or 10 k potentiometer as a voltage divider ground one end of the pot set the other end to 5 V and connect the slider to the gate gt Measure Ipss Adjust the pot until the gate is at ground while leaving the drain voltage at 10 V According to Eq 5 1 the drain current now equals by definition Jpss gt Measure Vp Using an ammeter to measure the drain current adjust the gate voltage until the drain current drops to zero The pinch off voltage will be equal to this gate voltage Why is this true gt Verify Eq 5 1 With the drain voltage set to 10 V adjust Vgs while measuring the drain current Plot Ip versus Vas The common source characteristic curves for the 2N5485 can be mea sured using the circuit shown in Fig 5 4 These curves illustrate the basic dependences among Ip Vps and Vgs and will be useful while performing the remaining exercises Since JFETs are notoriously variable more so than bipolar transistors try to use the same JFET for all exercises Use one pot to adjust the gate 70 Hands on electronics a b 0 15 V E 5to0V G S D S Fig 5 4 Circuit for measuring the common source characteristic curves voltage and the other to adjust the drain voltage Use the scope probes to measure the drain and gate voltages while using a meter to measure the drain
63. the first century and a half or so of electrical work The multimeters we use have various input jacks that accept banana plugs and you can connect the meter to the circuit under test using two banana plug leads The input jacks are described in Table 1 1 Depending on how you configure the meter and its leads it displays e the voltage difference between the two leads e the current flowing through the meter from one lead to the other or e the resistance connected between the leads Multimeters usually have a selector knob that allows you to select what is to be measured and to set the full scale range of the display to handle inputs of various size Note to obtain the highest measurement precision set the knob to the lowest setting for which the input does not cause overflow 2 Hands on electronics Table 1 1 Digital multimeter inputs Input jack Purpose Limits COM reference point used for all measurements VQ input for voltage or resistance measurements 1000 V DC 750 V AC mA input for current measurements low scale 200 mA 10A input for current measurements high scale 10A For the BK Model 2703B multimeters used in the authors labs To avoid damaging the meter be sure to read the safety warnings in its data sheet or instruction booklet 1 2 Breadboard Breadboard may seem a peculiar term Its origins go back to the days when electronics hobbyists built their circuits on wooden boards The breadb
64. the forward and reverse directions differ by a factor of 10 000 and that the voltage scale changes at large reverse voltage If a large enough reverse voltage is applied the junction breaks down and allows a large reverse current to flow the Zener effect When the P type material is at a more positive voltage than the N type material the diode is said to be forward biased this corresponds to V gt 0 in Fig 3 3 When the P type material is more negative than the N type material the diode is said to be reverse biased this corresponds to V lt 0 in Fig 3 3 Some useful approximations In the forward biased case when V is greater than 100 mV or so the 1 in Eq 3 1 becomes negligible compared with the exponential term and PATE 3 2 When the diode is reverse biased and V is greater than 100 mV or so the exponential term is negligible and the reverse current is almost constant with Ix I 3 3 35 3 Diodes 3 2 Types of diodes In addition to standard junction diodes light emitting diodes LEDs Schottky diodes and Zener diodes are also common LEDs are junction diodes typically made from gallium arsenide phosphide GaAsP They act very much like silicon junction diodes except that they emit light when conducting forward current and have forward voltage drops about twice as large as silicon diodes Infrared red orange yellow green and blue LEDs are commercially available Zener diodes
65. the same see Fig 9 1 b Whereas op amps are intended to be used with negative feedback the 311 is specifically designed for operation in open loop mode or with positive feedback The 311 s output stage differs from that of an op amp to enhance flexi bility it has both a positive output pin 7 and a negative output pin 1 We shall be using the positive output In this configuration a pull up resistor to a positive supply is required in order to determine the output voltage level and the negative output is generally connected to ground Note that the positive output is the collector of an NPN bipolar transistor As such it cannot source current but it can sink current When the output transistor is off i e its base voltage is less than or equal to its emitter voltage the collector is pulled up to V by the external pull up resistor Conversely when the base voltage is raised 0 7 V above the emitter voltage the transistor saturates and the output pin is pulled down close to the emitter voltage This output configuration gives the 311 maximum flexibility to provide the various signal voltages used by digital logic chips including TTL CMOS and ECL logic levels gt Start by choosing convenient values for V and V_ Use an input fre quency of 100 kHz and observe the output 1 Logic levels are discussed in section 10 1 1 115 9 Comparators and oscillators ESS 7 gt Change V and V_ Record and explain any chang
66. they can still cause trouble The key to safe work in electronics is always to estimate power dissipations in components before turning on the power and to make sure you are not exceeding the ratings 2 3 Potentiometer as voltage divider The voltage divider idea is very useful in analyzing almost all circuits so you will need to become thoroughly familiar with it A resistive voltage divider is simply two resistors in series see Fig 2 3 A voltage differ ence Vin is applied across the two and a smaller voltage Vout results at the junction between them A potentiometer can be used as a vari able voltage divider and you will now try this out using the breadboard s 10 k pot Warning You can easily burn out the pot in this exercise if you are not careful 1 Turn off the power before hooking up the circuit 2 If you accidentally connect the pot s slider to ground while one end is connected to the supply voltage or vice versa you can easily burn out Ry Vin A _ Vout Sa Vin 1 I R2 m Vout gt siden Vout SR potentiometer F atl Fig 2 3 Three schematics representing a resistive voltage divider In all cases you can show using Ohm s law that Vout Vin R2 Ri R2 Note that the far right representation is implemented using a potentiometer In this case the output voltage is variable and ranges between ground and Vin depending on the position of the slider 23 2
67. to zero volts The CH 1 and CH 2 menu buttons can be used to turn the display of each 12 Hands on electronics channel on or off they also select which control settings are programmed by the push buttons just to the right of the screen gt Display a waveform from the calibrator on channel 1 What happens when you adjust the POSITION knob The voLts pDiv knob 1 3 4 Horizontal sweep To the right of the vertical controls are the horizontal controls see Fig 1 4 Normally the scope displays voltage on the vertical axis and time on the horizontal axis The SEC DIv knob sets the sensitivity of the horizontal axis i e the interval of time per horizontal division on the screen The POSITION knob moves the image horizontally on the screen gt How many periods of the square wave are you displaying on the screen How many divisions are there per period What time interval corresponds to a horizontal division Explain how these observations are consistent with the known period of the calibrator signal gt Adjust the sEC pIv knob to display a larger number of periods Now what is the time per division How many divisions are there per period 1 3 5 Triggering Triggering is probably the most complicated function performed by the scope To create a stable image of a repetitive waveform the scope must trigger its display at a particular voltage known as the trigger threshold The display is synchronized whe
68. tracking 170 addition binary 141 algebra Boolean 126 140 141 alternating current 15 ammeter ideal 39 amplifier 50 common emitter 57 difference 95 differential 86 exponential 105 grounded emitter 59 inverting 168 op amp 88 logarithmic 105 noninverting 89 op amp 89 operational 79 85 amplitude 13 17 18 analog 167 analog information 167 analog to digital conversion 167 analog to digital converter 167 anode 35 54 arithmetic binary 125 126 141 assertion level logic 127 146 assertion level logic notation 146 astable multivibrator 120 156 asynchronous counter 151 157 attenuating probe 10 attenuation 10 26 77 attenuator 76 77 91 bandpass filter 123 bandwidth 87 base 48 BCD counter 157 bi quinary counter 157 bias current 94 binary addition 141 binary arithmetic 125 126 141 binary counter 156 157 binary search algorithm 171 binary coded decimal 157 bipolar junction transistor 47 bistable multivibrator 143 156 blocking capacitor 56 Boolean algebra 126 140 141 bounce contact 152 breadboard 2 breadboard LED indicators 137 breadboard level switches 137 138 breakpoint 26 buffer 55 push pull 62 200 Index buffering 55 capacitance code 20 capacitance parasitic 56 stray 115 capacitive reactance 19 capacitor 15 16 19 20 blocking 56 ceramic 16 electrolytic 16 mica 16 paper 16 polarized 16 types of 1
69. used so far have two and only two valid output states high and low Nowadays it is common for some logic ICs to have three output states There are situations in which the designer wishes the output to be neither high nor low Rather in such situations one wants to turn off the output completely i e the output should become a high impedance The third state is thus referred to as the high Z state This feature allows multiple outputs to be connected in parallel as long as all but one of them are in the high Z state A common example of the use of tri state outputs is the 150 Hands on electronics connection of multiple memory chips say 4 Mbytes each in parallel to build up a memory system say 64 Mbytes We can explore the third output state using the 74373 octal D type transparent latch IC The 373 is often used to drive a data bus and is equipped with three state outputs to allow the bus to be driven in parallel by multiple data sources drivers The eight output pins are driven by the IC when the output enable OE is held low and they go into the high Z state when OE is high The 373 is equipped with a latch enable LE instead of a clock Data are transferred from the input to the output while LE is high The outputs are latched held constant while LE is low This type of flip flop is called a transparent latch gt Begin by wiring the 373 as shown in Fig 11 6 If logic level switches are availab
70. used to measure current the DMM is equivalent to an ideal ammeter in series with a small input impedance Most ammeters will also have a series fuse to protect the meter When measuring voltage the DMM or oscilloscope looks like an ideal voltmeter in parallel with a large input impedance If the reverse current seems to be much bigger than you expect consider that you have a voltage measuring device a scope or voltmeter in parallel with the diode Fig 3 5 b gt Disconnect the scope or meter now how much current do you observe Reconnect it and disconnect the diode how much current flows with the scope or meter alone What do you infer to be the input resistance of the scope or meter Explain by applying Ohm s law to relate the voltage being measured to the current you observe Keep this experience in mind it is often necessary to consider the effect of your measuring device on the circuit being studied Can you see why an ideal voltmeter would have infinite resistance while an ideal ammeter would have zero resistance 40 Hands on electronics 3 6 Exploring rectification Next we take up the basic principles of rectification Almost all electronic equipment requires power from a steady voltage source i e a DC power supply For portable equipment the power is supplied by batteries How ever the most convenient power source is the 120 V 60 Hz AC line 120 V is in fact the r m s value of the sinusoidal volt
71. you have it oscillating look at both outputs on the dual trace oscilloscope gt Are the frequencies the same gt What is the phase relationship sine 3 3V 3 3V op amp cosine Cc 0 033 uF Fig 9 8 Sine cosine oscillator 123 9 Comparators and oscillators gt Measure the peak to peak voltage of the cosine wave Is it what you would expect considering the diodes being employed in the circuit Try to explain how the circuit works What role is played by the two back to back Zener diodes 9 2 3 Active bandpass filter Active filters have significant advantages over passive ones including e lower cost due to replacement of expensive inductors by capacitors phase shifted via feedback e high input impedance and low output impedance e ease of tuning over a wide frequency range They also have significant disadvantages such as frequency response lim ited by the bandwidth of the op amp and the need to provide power to the op amp There are a variety of configurations that can be used for low pass high pass and bandpass applications for a more extensive discussion see e g Horowitz and Hill The Art of Electronics or Simpson Introductory Electronics for Scientists and Engineers Wire up the circuit of Fig 9 9 apply power and drive it with a sine wave of about 1 V peak to peak Vary the driving frequency until you find the maximum output amplitude What are the center frequency fo and upper and lower
72. 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 t 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Analog 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 aa 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Digital 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 kay 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 80 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 m 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Speaker hes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 hes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 m 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 hes 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
73. 00 Hz gt Record describe and explain the appearance of the output signal at this frequency gt Measure the peak to peak output voltage and determine the voltage gain comparing with what you would expect theoretically 108 Hands on electronics EEE gt Sketch the input and output waveforms at 10 kHz and 100 Hz and comment on your results At what approximate frequency will this circuit cease to act as an integrator i e approach the operation of an inverting amplifier gt Compare the output amplitudes with the theoretical expectation 8 2 2 Logarithmic and exponential amplifiers Set up the circuit of Fig 8 6 with R 10 k or Fig 8 7 with R 10 k Figure out how to apply an adjustable DC input voltage gt Verify the logarithmic or exponential gain characteristic for several input voltages that probe the full range of output voltage of which the circuit is capable gt Explain how the circuit works and derive an expression that relates the input voltage to the output voltage gt Make a semilog plot of your data and find the experimental value of n for your diode gt The log of zero is undefined and any number raised to the power zero equals one Why then do the logarithmic and exponential amplifiers give an output of zero volts when the input is zero volts 8 2 3 Op amp active rectifier Fig 8 8 a shows a simple op amp half wave rectifier gt Build it with R 10 k and try it out with a low frequency si
74. 1 dQ P 2 4 a 2 4 dv Zg 2 5 7 2 5 SE ais 2 6 TA iene wC Vo cos wt 2 7 wCVp sin wt 90 2 8 We see that the current is also a sine wave but shifted in time with a phase shift of 90 i e the current leads the voltage by 90 We can write an Ohm s law equivalent for a capacitor as long as it is understood that we are talking about sinusoidal waveforms only Vo 10Xc 2 9 1 Of course this is only an idealized approximation since in any real circuit there is at least the resistance of the wires and in practice any signal source has some internal resistance 19 2 RC circuits where Jp is the amplitude of the current sine wave and Xc 1 wC is the capacitive reactance of the capacitor The reactance is thus the effective resistance of the capacitor Note that it is frequency dependent in keeping with our intuition that for DC a capacitor should look like an open circuit infinite resistance while at high frequency it should approach a short circuit zero resistance For completeness we mention here the inductive reactance X wL where L is the inductance of an inductor Inductors are coils of wire and satisfy the equation 2 10 Just as capacitors often employ a dielectric inductors are often wound on a ferrite core to increase their inductance Note that the inductor equation relates the voltage across an inductor to the derivative of the current through it while the capacitor equat
75. 45 147 148 149 12 Contents 11 5 Flip flop applications 11 5 1 Divide by four from JK flip flops 11 5 2 Contact bounce 11 5 3 Electronic coin toss Monostables counters multiplexers and RAM 12 1 Multivibrators 12 2 Counters 12 3 Experiments 12 3 1 Bi quinary ripple counter 12 3 2 Monostable multivibrator 12 3 3 Multiplexer and finite state machine 12 3 4 RAM 13 Digital analog conversion 13 1 A simple D A converter fabricated from familiar chips 13 2 Tracking ADC 13 3 080x ADC and DAC chips 13 3 1 Successive approximation ADC 13 4 Additional exercises 13 4 1 Digital recording 13 4 2 Successive approximation ADC built from components Further reading Appendix A Equipment and supplies Appendix B Common abbreviations and circuit symbols Appendix C RC circuits frequency domain analysis Appendix D Pinouts Glossary of basic electrical and electronic terms Index 151 151 152 153 155 156 156 157 157 159 162 162 167 168 170 171 171 177 177 178 183 185 188 191 194 197 199 1 1 1 2 1 3 1 4 2 1 2 2 2 3 2 4 25 2 6 3 1 3 2 3 3 3 4 3 5 3 6 3 7 3 8 3 9 3 10 3 11 3 12 4 1 xi Figures Illustration showing many of the basic features of the PB 503 powered Protoboard Measuring voltage Measuring current Illustration of the Tektronix TDS 210 digital oscilloscope Representation of an arbitrary periodic waveform Circuit demonstrating destructive p
76. 6 carry in 156 carry out 156 157 cascaded counters 156 cathode 35 54 clipping 77 closed loop 89 CMOS 125 CMOS ICs powering 136 CMOS logic 133 CMOS TTL 133 CMRR 78 96 97 collector 48 common emitter amplifier 57 common mode 78 common mode gain 78 common mode rejection 78 common mode rejection ratio 78 96 comparator 113 311 114 voltage 113 magnitude 142 compliance 59 71 contact bounce 152 conversion analog to digital 167 digital to analog 167 converter analog to digital 167 digital to analog 167 counter 151 152 156 74191 168 asynchronous 151 157 BCD 157 bi quinary 157 binary 156 157 decade 157 cascaded 156 decimal 157 158 four bit 157 negative edge triggered 157 ripple 151 157 synchronous 152 157 two bit 151 156 crossover distortion 63 109 CRT 9 current mirror 79 current source FET 70 op amp 97 transistor 59 current source load FET 72 CY62256 memory 177 D type flip flop 147 DAC 167 DAC0806 174 DACO080x 178 family 174 Darlington 61 data selector 162 DC coupling 79 85 DC offset 87 debouncer switch 153 debugging 144 debugging digital logic 144 decade counter 157 decibel 26 83 decimal binary coded 157 decimal counter 157 158 decoder 178 74138 178 delay propagation 148 DeMorgan s theorem 141 146 diagram state 143 timing 143 dielectric 16 dielectric constant 16 difference amplifier 95 differential ampl
77. America the supply voltage from a standard wall socket is 120 V and the supply frequency is 60 Hz the discussion is equally valid for other values which may be substituted according to your local supply voltage and frequency 41 3 Diodes Transformer fuse 120 8 Vac Fig 3 6 a Power transformer supplies Vou 25 V r m s b waveform produced by the circuit in a the current drawn and its 25 2 V r m s nominal output voltage is for sub stantially higher current than is drawn by the 10 k load gt Add a 1N4001 diode to give the half wave rectifier of Fig 3 7 a with Ry 10k gt Observe and record the voltage waveform Measure the amplitude Vo using the oscilloscope due to the rectification it is now equal to the peak to peak voltage gt Compare the amplitude of the half rectified waveform with the amplitude of the unrectified waveform measured above By how much has the amplitude decreased Is this the amount you expect Explain gt Measure the average voltage Va across the load with a DC voltmeter Check that for a half wave rectifier V Vee 3 12 JTT gt Add a filter capacitor in parallel with the load as shown in Fig 3 8 a Caution The 100 uF electrolytic capacitor is polarized be careful not to hook it up backwards The negative terminal should be labeled with a sign 42 Hands on electronics Transformer Rectifier Diode lt Fees Fe we 1 fuse i R F 12 L
78. Emitter follower Emitter follower with optional load circuit for measurement of Zout Common emitter amplifier Transistor current source Transistor switch Darlington pair Driving loudspeaker with push pull buffer Common base amplifier Construction and circuit symbols of JFETs Schematic representation of JFET operation Idealized common source characteristic curves for a JFET Circuit for measuring the common source characteristic curves Self biasing JFET current source Source follower Source follower with current source load JFET amplifier Differential amplifier and function generator with 100 to 1 attenuator Current sink for differential amplifier Current mirror Differential amplifier with current mirror load Differential amplifier with Wilson current mirror load Diagram of 8 pin DIP 741 package showing pinout Op amp inverting amplifier circuit Op amp noninverting amplifier circuit Open loop op amp test circuit Circuit for demonstrating summing junction Op amp voltage follower and voltage follower as the input stage to an inverting op amp circuit Difference amplifier Op amp current source Fancy summing circuit Generalized op amp inverting amplifier circuit 49 51 55 55 56 57 59 60 62 63 64 66 67 67 70 71 72 73 73 76 79 80 81 82 86 88 89 91 93 95 96 98 99 102 xiii 8 2 8 3 8 4 8 5 8 6 8 7 8 8 8 9 8 10 9 1 9 2 9 3 9 4 9 5
79. IL311 as you vary the input voltage What do you observe gt How should the comparator inputs be configured which signal should go to the inverting and which to the noninverting input Is the output number homing in on the expected value If not did you perhaps connect the comparator backwards Explain and if you did it wrong the first time fix it gt Record the output numbers for a few different input voltages gt Why is the output number never stable How if at all does this affect the precision of the voltage measurement Note that the tracking ADC is slow at following large input voltage changes since it has to count through all the intermediate values but it has good performance if the input voltage changes gradually 171 13 Digital lt gt analog conversion a i Analog In 10 KQ 1 MQ Fig 13 2 Simple A D converter The polarity of the comparator inputs is left as an exercise for the reader 13 3 080x ADC and DAC chips 13 3 1 Successive approximation ADC The technique just described is comparable to looking for a word in the dictionary by looking at each word one after the other until you find the right one or if the word you re looking for isn t in the dictionary until you find a word beyond the one you re looking for As we ve seen this is a fine algorithm for tracking a slowly changing signal but if the DAC is far from the signal voltage it takes a long time to home in A faster
80. PB 503 have a bank of SPST DIP 5 5 1 100 k SPDT TTL or CMOS Switch LOGIC LEVEL SPST Switch er TTL or CMOS LOGIC LEVEL Fig 10 10 Logic level switch using either an SPST or SPDT switch and a pull up resistor as shown 138 Hands on electronics switches instead of logic switches If your breadboard doesn t have logic switches refer to Fig 10 10 for details on how to use the SPST switch bank as logic level switches gt Figure out how to use the logic level switches to turn an LED indicator on and off Explain how the indicator works CMOS inputs require well defined input voltages therefore a CMOS input must always be connected either to power or ground or to a CMOS or in some cases TTL output Unpredictable behavior as well as exces sive current flow from the power supply to ground will result otherwise TTL is more forgiving and SPST switches can easily be used as TTL level switches even without a pull up resistor As we will explore in more detail later an unconnected TTL input usually behaves as if connected to a logic high you assert a TTL low logic level at an input by con necting it to ground whereas an open input acts like a high logic level With one end of the SPST switch connected to ground you can thus set the switch on to assert a TTL low input level or off to assert a TTL high 10 3 2 MOSFETs To demonstrate MOSFET behavior construct the circuits shown in Fig 10 11 gt For
81. R 4R 8R 16R 32R 64R and 128R For 8 bit accuracy these need to have better than 0 5 tolerance The DACO806 175 13 Digital lt gt analog conversion 15V 4 7 KQ Output 4 7 KQ DAC0806 Fig 13 4 Pinout for the DACO80x series of D A chips with an output op amp added Note that the bit order is the reverse of that used for the ADCO80x such that AO is the MSB and A7 the LSB also has eight resistors but their tolerances are not as good such that the DAC0806 is not guaranteed to put out 256 distinguishable voltage levels but only sixty four These chips also contain circuitry to buffer the input signals and stan dardize their voltage levels to avoid inaccuracies due to voltage variations in logic levels on different input lines Consult the manufacturer s data sheet to see what else your D A converter chip contains gt Wire up a DACO80x chip as shown in Fig 13 4 This configuration will give an output voltage between 0 and 5 V Connect the outputs of the ADC you built above to the inputs of the DAC gt What is the output voltage that corresponds to the DAC digital input 00000001 What is the output voltage that corresponds to the digital input 11111110 Take a few more data points and plot output voltage versus digital input Comment on your results gt Measure the precision of your DAC Does it match the specified precision gt Be sure to write down a complete circuit diagram with pin numbers Explain in your
82. RC circuits the pot briefly explain why this is true Hint how much power can be dissipated in the pot in such a situation 3 If you connect the multimeter on a current or resistance setting between the slider and some other point in the circuit while the circuit is powered you can easily burn out the pot since on these settings a meter can act as a low impedance short circuit 2 3 1 DC voltage divider First use the ohmmeter setting of your multimeter to measure the resistance between the slider and each end of the 10 k pot Turn the knob to set the slider exactly half way between the ends using the meter to tell you when you get there Next use the voltmeter setting to adjust the variable positive power supply to 10 V Then turn off the power connect one end of the pot to ground and connect the other end to 10 V Connect the meter on the volt age setting between the slider and ground Double check your connections gt Without moving the slider or changing the supply voltage turn on the power and measure the voltage between the slider and ground gt What are the values of R and R2 Using the voltage divider equation R Vout Vin za 2 13 Ri R2 explain why the predicted output voltage is 5 V How close to this prediction is your measured voltage What is the percentage error 2 3 2 AC voltage divider Now verify that a resistive voltage divider works the same way for AC as for DC Apply a sinuso
83. a differential amplifier made of two NPN transistors You can think of it as a current divider Quiescently the current through R is shared equally between Q and Q2 If a differential input signal is applied to the bases of Q and Q2 some collector current shifts from one transistor to the other This change AZ causes a positive voltage change at one collector and a negative voltage change at the other i e a differential output signal as explained in more detail below 6 1 2 Expected differential gain The differential voltage gain can be understood as follows Suppose we apply a differential signal consisting of equal and opposite changes in the base voltages of Q and Q2 A Ving AVin AV 6 1 Since the emitter voltages follow the base voltages a similar voltage change occurs between the two emitters This causes a current AJ to flow across the two emitter resistors Since these are in series with the dynamic emitter resistances of the two transistors each of which has an approxi mate value re 1 g 25mV Ic according to the Ebers Moll model we have AI AV Rp ro 6 2 77 6 Transistors Ill differential amplifier Since a purely differential signal raises the voltage at one emitter by the same amount that it lowers the voltage at the other emitter it does not change the voltage at the top of R thus the current through R is constant This means that the current due to the differential signal must
84. acitor Estimate the value of the stray capacitance Replace the 50 pF capacitor gt Write a complete circuit diagram with pin numbers and explain in your own words how this circuit works Comment on your observations and measurements Save your ADC circuit for use in the next part The DACO80x D A converters The DACO80x is a family of popular D A converter chips of which the DAC0806 is the least expensive it is an 8 bit DAC with 6 bit precision while the related DAC0807 and DAC0808 have 7 and 8 bit precision re spectively Our home brew D A converter above used 4 bits to distinguish sixteen different voltage levels With the DACO806 we can distinguish not sixteen but sixty four different voltages at least If you need more accu racy you can use the DAC0807 the DAC0808 or one of the more sophis ticated chips that are available You may use whichever of these chips is available for this exercise Chips of the DACO80x family output a current that is proportional to the value of the digital input Some D A converter chips e g the expen sive and less readily available NE5018 include an op amp on the same chip The DACO80x family does not To convert the DAC s output cur rent to an analog voltage you can use an external op amp as shown in Fig 13 4 What exactly is the difference between the top of the line DACO808 and the budget DAC0806 Within the DAC0808 chip are eight resistors of nominal resistance R 2
85. age the amplitude being Vo V2 x 120 V 170 V 3 10 and the peak to peak voltage is of course twice this or Vp p 340 V as you can easily verify from the definition of the root mean square by integrating over the sine wave Within most electronic equipment using the AC line there is a power transformer that steps down the 120 V AC to a more convenient voltage a rectifier that converts the alternating voltage from the transformer to a DC voltage and a regulator that maintains the output voltage at the desired level Caution In using a power transformer bear in mind that an especially large transient current sometimes flows when the line cord is first plugged in You will probably blow fewer fuses if you leave the power transformer plugged in at all times Attach banana plug leads to the transformer s sec ondary only after you are sure your circuit will not damage any of the equipment Do not permit powered lines to dangle loosely when reconfig uring your circuit it is safest to disconnect the leads at the transformer not at the breadboard gt Set up the circuit shown in Fig 3 6 a using a 10 k resistor as the load R Observe the sinusoidal voltage waveform across R Measure the amplitude Vo and the r m s voltage Check the relation 2Vims Vo 3 11 You will probably find Vims gt 25 V Since the windings of the transformer have some ohmic resistance the transformer s output voltage depends on 1 In North
86. aging components Voltage is related to potential energy difference The voltage drop across any circuit element is directly proportional to the change in energy of a charge as it traverses the circuit element Specifically 1 volt 1 joule coulomb The potential energy with respect to some reference point is equal to the voltage multiplied by the charge Current refers to the motion of charges The current through a given surface e g the cross section of a wire is defined as the net charge passing through that surface per unit time The unit for current is the ampere l ampere 1 coulomb second The product of voltage and current has units of joules second otherwise known as watts If the voltage drop across a circuit element equals the change in poten tial energy per unit charge and the current equals the amount of charge 21 2 RC circuits moving through the element per unit time then their product equals the power released within the device The power dissipated within any device is given by P IV 2 11 For resistive elements or when an effective resistance can be defined Eq 2 11 can be combined with Ohm s law to give P IV IPR V R 2 12 Resistors diodes transistors relays integrated circuit chips etc are rated in part by their maximum allowed power Exceeding these ratings can have disastrous effects on your circuit and may even cause a fire To illustrate this point our first ex
87. ake you three to four times as long Apparatus required 143 The ideas explored in the following exercises apply equally whether CMOS or TTL gates are used use whichever is most convenient You will need a quad NAND 7400 a dual D type flip flop 7474 and a dual JK flip flop 74112 In addition you will need a 74373 a breadboard two 1 k 1 W resistors and a two channel oscilloscope with two attenuating probes If possible avoid unnecessary complications by not mixing CMOS and TTL chips within a single circuit 144 Hands on electronics EEE 11 1 General comments 11 1 1 Schematics For each of the following exercises be sure to write down a complete schematic diagram of each circuit you build including pin numbers but power and ground connections need not be shown Often when one wires up a circuit off the top of one s head it fails to work Writing down the schematic showing all pin numbers is a powerful debugging tool since it makes incorrect connections much more obvious 11 1 2 Breadboard layout To keep your breadboard organized it is a good idea to use one vertical bus for power and another for ground so that power and ground connections to each chip can be made with short jumpers A neat layout is easier to debug than a messy one Remember that the top and bottom busses on the PB 503 are not connected internally 11 1 3 Synchronous logic The circuits in this chapter introduce the concept of synchronous
88. alculate what you expect and compare At the breakpoint or half power frequency fo RC 1 and thus the attenuation is 1 2 0 707 This is also referred to as the 3 dB point since it is the frequency at which the output voltage is attenuated by 3 dB The breakpoint is a convenient way to parametrize simple filters The decibel is a logarithmic measure of the ratio of two signals A2 number of dB 20 log T 1 where A is the amplitude of the first signal and A is the amplitude of the second in this case A Vin is the amplitude of the output signal and Az Vout is the amplitude of the input signal gt By varying f until the output amplitude is 70 7 of the input ampli tude measure fo Calculate what you expect and compare with your measurement gt What are the attenuation and phase shift at low frequency say 50 Hz Compare with the predictions of Eq 2 22 Compare the phase shifts with R arctan ah 2 23 c The phase shift at low frequency is easy to understand in the limit of DC the capacitor must act like an open circuit i e infinite impedance and thus does not affect the output signal Conversely in the high frequency limit the capacitor must look like a short circuit to ground so the output signal goes to zero and the phase shift becomes dominated by the capacitor 27 2 RC circuits 2 7 RC circuit as differentiator Now interchange the capacitor and resistor so that the input signal is applied at
89. am a Fig 3 4 Representation of physical diodes along with the symbols used in circuit diagrams 36 Hands on electronics Table 3 1 A diverse selection of diodes is commercially available of which a tiny sampling is given here Diodes are commonly rated by their switching speed maximum power dissipation maxi mum forward current maximum forward voltage at a specified forward current and reverse breakdown voltage The junction capacitance is sometimes listed as well Pmax Tmax Vemax IF Var C Diode Type W A V A V pF 1N914 small signal 0 5 0 3 1 0 0 01 75 4 0 1N4001 rectifier 1 0 1 1 1 0 50 8 0 1N4004 rectifier 1 0 1 1 1 0 400 8 0 1N5402 rectifier 3 0 1 1 3 0 200 40 FR601 fast rectifier 6 0 1 3 6 0 50 200 MBD301 Schottky 0 28 0 1 0 6 0 01 30 1 0 1N4733A Zener 1 0 1 2 0 2 5 1 switch from forward to reverse bias or vice versa A few examples are given in Table 3 1 3 3 Rectification A rectifier is a device that converts AC to DC by blocking the flow of current in one direction Rectification used to be almost the exclusive province of vacuum tubes with the exception of the detector crystals naturally occurring semiconductor diodes used in crystal sets in the early days of radio Nowadays semiconductor diodes are universally used for the purpose An ideal rectifier would offer zero resistance when forward biased i e the voltage across it would be zero independent of the amount of
90. at Illinois Institute of Technology to a mix consisting mostly of physics mechanical engineering and aeronautical engineering majors Each experiment can be completed in about four hours with one or two additional hours of preparation This book differs from existing books of its type in that it is faster paced and goes into a bit less depth in order to accommodate the needs of a one semester course covering the elements of both analog and digital electron ics In curricula that normally include one year of laboratory instruction in electronics it may be suitable for the first part of a two semester sequence with the second part devoted to computers and computer interfacing this scheme has the virtue of separating the text for the more rapidly changing computer material from the more stable analog and digital parts The book is also suitable for self study by a person who has access to the necessary equipment and wants a hands on introduction to the subject We feel strongly and experience at IIT has borne out that to someone who will be working with electronic instrumentation a hands on education in the techniques of electronics is much more valuable than a blackboard and lecture approach Certainly it is a better learning process than simply reading a book and working through problems The appendices suggest sources for equipment and supplies provide tables of abbreviations and symbols and list recommendations for fur ther reading
91. at best clarifies the operation of the circuit gt Build and test your flip flop and record its state table what its outputs do for each of the four possible input states Keep in mind that what the flip flop does for a given input may depend on past history so try a few different sequences of input states to make sure you understand what it is doing In other words to see the entire state table you need to try each input state for each of the flip flop s two internal states gt How would the flip flop s operation be different if it were made of positive logic NORs You don t need to build this circuit to answer the question Leave the RS latch in place for use later in this chapter 147 11 Flip flops LSS R S C D JQiy Qr H H L XQ Q H H H X Q WKH X XL H H x X XJH L clk clk L L X X H H H H 4 LJL H H H f HJH L Vec pin 14 P X Don t Care Gnd pin 7 but note that the state after LL input condition is removed depends on which input signal goes high first if both go high simultaneously state is undefined Fig 11 3 7474 D type flip flop with state table T es A A Nout ut state fouomissubie f OUT ______ J P between rising L is not specified rg e u N preceding the first clock edges rising clock edge due to changing input IN ios 7 minimum setup time 1 gt not satisfied p CLK Fig 11 4 Sample timing diagram for a positive edge triggered 7474 D type flip
92. at the input the current mismatch between Q2 and Qs must flow through the 10 M scope probe input impedance You should then see an enormous differential gain If Q5 were an ideal current source the gain would be 10 M 2r gt Explain the last statement 81 6 Transistors Ill differential amplifier Eas 15 2N3906 Qs 1N4733 5 1V 15 Fig 6 4 Differential amplifier with current mirror load In practice the collector of Qs will have an output impedance less than 10 M and so the gain will be lower You may find it desirable to increase the attenuation of your input voltage divider from 100 to 1000 here Also to avoid clipping of the output signal you will want to arrange for the quiescent collector voltage of Q2 to be around 7 V you can adjust it by hooking up the base of Q2 not to ground but to the wiper of the 1 k pot with one end of the pot connected through a resistor to 15 V and the other end connected through a second resistor to 15 V as shown in Fig 6 4 Due to the high gain of this amplifier the output voltage will be sensitive to small variations at either input If you observe a DC output signal near either ground or 15 V it is likely that you need to fine tune the offset voltage using the 1 k pot Also note that a gain value approaching 1000 is not unreasonable gt What gain do you observe Compare with the gain you would expect if Q s effective load were 10 M What effective load resistan
93. atures to be used in this tutorial are marked Note and remember the location of the AUTOSET button when all else fails try autoset cathode ray tube CRT While the TDS210 can perform a similar function it does not contain a CRT part of the reason it is so light and compact Until the 1990s most oscilloscopes were purely analog devices an input voltage passed through an amplifier and was applied to the deflection plates of a CRT to control the position of the electron beam The position of the beam was thus a direct analog of the input voltage In the past few years analog scopes have been largely superseded by digital devices such as the TDS210 although low end analog scopes are still in common use for TV repair etc A digital scope operates on the same principle as a digital music recorder In a digital scope the input signal is sampled digitized and stored in memory The digitized signal can then be displayed on a computer screen One of your first objectives will be to set up the scope to do some of the things for which you may already have used simpler scopes After that you can learn about multiple traces and triggering In order to have something to look at on the scope you can use your breadboard s built in function generator a device capable of producing square waves sinusoidal waves and triangular waves of adjustable amplitude and frequency But start by using the built in calibrator signal pro
94. bitrary bipolar transistor Study their shapes carefully and refer to them as you perform the following exercises 4 1 2 Simplest way to analyze transistor circuits In the following section we consider a mathematical model the Ebers Moll model that gives a good approximation to transistor performance However you don t need the model to understand transistor operation in most circuits We will see from the Ebers Moll model that if a transistor Breakdown Saturation Linear Breakdown PENER Ty Ig 35 mA J Linear Ig 350 pA mA 3 Tg 250 uA 107 5 10 15 20 Voe 5 10 15 20 Vos Volts 0 Volts Fig 4 3 Characteristic curves for an NPN bipolar transistor 52 Hands on electronics is on and conducting milliamperes of collector current its base emitter voltage difference Vgg is approximately constant at about 700 mV Fur thermore the base is a point of high impedance whereas the emitter is a point of low impedance Thus a changing voltage at the base causes matching voltage changes at the emitter In other words the base voltage controls the emitter voltage e the emitter voltage follows the base Since is large e the collector current nearly equals the emitter current Since the collector is of even higher impedance than the base e the collector assumes any voltage required by Ohm s law as applied to the rest of the circuit These three rules are all you need to know in most sit
95. ce between the two signals is amplified This follows since if these inverting and non inverting amplifiers have equal gains the output is proportional to the dif ference of the inputs The gains are matched provided that R R2 R3 R4 96 Hands on electronics Vout Fig 7 7 Difference amplifier The parts of the pot on either side of the slider serve as R3 and R4 Difference amplifiers are often used in the life sciences where signals are small and exist within a noisy environment e g in the electrocardiograph ECG Any background noise common to both inputs common mode noise is rejected while the signal of interest present at only one of the inputs is amplified and appears at the output A potentiometer is often used as in Fig 7 7 to tune the gain and common mode rejection of the amplifier The quality of the amplifier is measured in part by the common mode rejection ratio CMRR based on the ratio of the differential voltage gain and common mode voltage gain CMRR 20 log Agite ACM 7 7 It is customary to give the CMRR in decibels as shown in Eq 7 7 The 741 general purpose op amp is a differential amplifier with a CMRR value specified to be at least 70 dB Precision op amps are commercially available with CMRR values as high as 140 dB or more Build the circuit shown in Fig 7 7 As always be careful not to short the potentiometer s center tap to ground or power You can estimate the common mode rej
96. ce do you infer Is this consistent with the dynamic resistance of the current mirror output you observed in section 6 2 1 gt The sensitivity of this circuit is easily demonstrated Try warming either Q4 or Qs by gently squeezing the transistor between your finger and thumb Observe how the output changes and suggest an explanation for your observation Try doing the same for the other transistor 82 Hands on electronics SS 6 2 3 Improved current mirror You can improve the output impedance of your current sources by adding a small resistor in series between the positive supply and the emitter of each PNP transistor gt Try this with two 100 Q resistors and see by how much the gain increases What effective load resistance do you infer now 6 2 4 Wilson current mirror You can do even better by converting the simple current mirror to a Wilson current mirror Do this by adding a third PNP transistor as shown in Fig 6 5 This clever circuit beats the Early effect by fixing Q5 s Vcr at the same time it also symmetrizes the base current mismatch of the simple current mirror Explain gt Try this to see by how much the gain increases Note that you will need to re tune the collector voltage of Q2 by adjusting the offset voltage What effective load resistance do you infer now 1N4733 5 1V 15 Fig 6 5 Differential amplifier with Wilson current mirror load 83 6 Transistors Ill differential amplifier
97. ce to ground at the noninverting input gt Be careful not to be confused by the DC shift in the output produced by the 1 M input resistor Explain how this shift results from the op amp s input bias current What value for the input bias current is implied by the observed DC shift The output impedance should of course be the same as for the inverting amplifier since as far as output impedance is concerned it is the same circuit gt Explain this last statement Hint what was the only thing you had to change to make the noninverting amp from the inverting amp 7 2 4 Voltage follower As shown in Fig 7 6 a connect the output of the op amp directly to the input and connect the output of the function generator to the input of the op amp gt After turning on the power confirm that the input and output signals are identical and that the voltage follower is noninverting Record the input and output amplitudes gt Of what possible use is an amplifier of unity gain that does not even invert the signal As an illustration of the voltage follower s usefulness coil a long wire 30 to 50 cm in length around the outside of an AC power cord Any power cord will do provided that it is plugged in The breadboard cord is usually the most convenient Leave one end of your coil floating and connect the other to any convenient spot on the breadboard gt Using your scope probe observe the waveform Record and ex
98. ction is useful when sensing a small signal in the pres ence of noise since often the noise is in common on both inputs and can be subtracted away by a differential amplifier Test the common mode rejection of your differential amplifier gt Connect both inputs to the same sine wave from the function genera tor i e Ving Vin_ What do you observe at the outputs You should see almost identical signals on both outputs What common mode gain Acm AVout AVin and Acm AVou AVin do you ob serve for each output and why Common mode rejection is usually specified in terms of the common mode rejection ratio expressed in decibels Adif CMRR 20 logy 6 3 Acm gt What value of CMRR do you observe Although the common mode gain of this circuit is small it can still be a nuisance in practice It could be reduced by increasing the size of R4 but that would reduce the amount of current flowing through Q and Qo increasing re and reducing the differential gain A better solution is to replace R with a current source shown in Fig 6 2 Try this gt Measure how much current your current sink sinks calculate what you expect and compare 1 Strictly speaking it is a current sink since positive current flows into the collector as indicated 79 6 Transistors III differential amplifier 2 mA 560 2N3904 1N4733 5 1 V 2 2k 15 Fig 6 2 Current sink for differential amplifier gt What ou
99. cuit in its synchronous form Fig 11 8 gt Use the scope to confirm that the ripple is gone and make a timing diagram showing this You can see that unlike D flip flops JK flip flops are natural for building synchronous counters explain Keep your synchronous counter and RS latch for the next exercise 11 5 2 Contact bounce When a mechanical switch closes or opens there is usually an effect called contact bounce This means that the switch closes and opens repeatedly for a period of order milliseconds until the contacts settle down This makes no difference if you are turning on a light but if you are sending a clock pulse to a counter made of high speed devices the counter can react to each bounce and therefore count a random number of times First use the scope to observe contact bounce directly Hook up an SPDT single pole double throw switch as in Fig 11 9 a gt Set the scope s sweep rate in the vicinity of 0 1 to 1 ms division use normal triggering and look at the output of the switch as you open and close the contact Play with the trigger threshold and sweep rate 153 11 Flip flops I Fig 11 9 a Looking at contact bounce by driving a divide by four counter from a switch b A NAND latch is used as a debouncer to see if you can discern the bounces Make a sketch of the observed waveform gt Next clock your two bit counter from the switch and see what happens Write down some typical seque
100. current gt Using the pot adjust Vgs to be 0 5 V more positive than Vp keep in mind that Vp is negative Slowly increase the drain voltage from zero to 15 V while measuring the drain current Record and plot your measurements For Vps less than a few volts the current should increase linearly with drain voltage This is the linear region in which the JFET acts as a voltage controlled variable resistor As you further increase Vps the current should then saturate at an approximately constant value JFET saturation occurs because the increasing drain voltage creates an increasing depletion region between the gate and drain Since Ves gt Vp the channel will never be pinched off completely with an equilibrium of sorts created The size of the depletion region and thus the resistance of the channel increases approximately linearly with drain source voltage difference resulting in approximately constant current gt Repeat your measurement procedure for several Vgs values between Vp and zero Plot the data on a single graph and clearly label each curve indicating the linear region the saturation region and Jpgs 5 2 2 FET current source Adding a resistor improves the JFET s current source performance com pared with that of the bare JFET gt Hook up the circuit shown in Fig 5 5 and measure the dependence of the drain current on the drain source voltage as you adjust the pot record and plot your measureme
101. d 15 V blue jack have a common 4 Hands on electronics Le ground connection black jack The 15 V and 15 V supplies are actually adjustable using the knobs provided from less than 5 volts to greater than 15 volts 1 2 1 Measuring voltage Voltage is always referenced to something usually a local ground For the following exercises you will measure voltage with respect to the breadboard ground which is also the common ground for the three power supplies To measure a voltage you will first connect the common jack of the meter to the breadboard common i e breadboard ground Next you will connect the meter s voltage jack to the point of interest The meter will then tell you the voltage with respect to ground at this one point When connecting things it s always a good idea to use color coding to help keep track of which lead is connected to what Use a black banana plug lead to connect the common input of the meter to the ground jack of the breadboard black banana jack labeled with a lt gt or symbol Use a red banana plug lead with the V input of the meter Since the DMM is battery powered it is said to float with respect to ground i e within reason one may connect the DMM s common jack to any arbitrary voltage with respect to the breadboard ground It is therefore possible to measure the voltage drop across any circuit element by simply connecting
102. d idea here to use the ground clips on your Oscillations High 15 Fig 9 2 311 comparator with 10 k series input resistor The capacitor shown connecting the input and output represents the stray capacitance associated with the breadboard Do not add a discrete capacitor 116 Hands on electronics scope probes to suppress pickup of the large transient pulse due to the 15 V swing of the 311 s output You ll want to look at a low to high or high to low transition and zoom in by increasing the time sensitivity to look for the rapid multiple transitions that indicate oscillation gt Vv Starting with an input frequency near 100 kHz and an amplitude of several volts gradually reduce the input amplitude and frequency until oscillations are observed To be able to see the rapid transitions of the output be sure the time scale on your oscilloscope is about 500 ns per division or less Sketch the observed oscillations What is the time scale of the oscill ations i e what is the period Ar for one cycle of the oscillation waveform How small an input slope does it take to cause oscillation What causes the oscillations to stop Why is a 741 configured as a comparator less likely to oscillate than the 311 9 1 3 Intentional positive feedback Schmitt trigger The oscillation problem can be eliminated by adding controlled positive feedback hysteresis as shown in Fig 9 3 The hysteresis also makes t
103. d schematically in terms of logic gates as well as with truth tables in Fig 10 4 10 2 CMOS and TTL compared 10 2 1 Diode logic We begin our consideration of the electronic implementation of logic gates with the simplest example Since diodes pass current in only one direction they can be used to perform logic as shown in Fig 10 5 Assuming logic levels equal to either 0 or 5 V it is easy to show that the output voltage is near 5 V actually one diode drop below 5 V if both inputs are 5 V and zero otherwise If we assume the positive logic convention high true low false this is equivalent to a logic AND of the two inputs You may want to verify this by building this circuit on a breadboard and trying it out 132 Hands on electronics E 5 3 3k A B Fig 10 5 Two input diode gate 5 Fig 10 6 Diode transistor NAND gate using 2N3904s This resembles the circuitry actually used inside the 7400 except that in the 7400 a two emitter transistor substitutes for the input diodes The resistor values are approximate and vary with TTL family Also shown is a simple LED logic level indicator being driven by the NAND gate s output 10 2 2 Transistor transistor logic TTL Using the diode logic concept as an input stage TTL logic was developed during the 1960s A TTL inspired NAND gate constructed using diodes and bipolar transistors is shown schematically in Fig 10 6 The operation of the circuit
104. data sheets for details Note that the LED logic indicators built into the PB 503 operate in positive logic whereas for TTL home built logic indicators as in Fig 10 6 operate in negative logic 10 2 3 Complementary MOSFET logic CMOS In the 1970s a new family of logic chips was developed using MOSFETs instead of bipolar transistors The basic MOSFET logic gate uses comple mentary N channel and P channel MOSFETs and is thus called CMOS Fairchild first introduced the 4000 series of CMOS logic but the popularity of TTL led manufacturers to develop TTL like CMOS families such as the 74C 74HC 74HCT 74AC and 74ACT The families with a T in their part numbers are fully compatible with TTL logic levels while the ones without a T are logic and pinout compatible with TTL but operate with CMOS logic levels Since the 1990s CMOS logic ICs have surpassed TTL logic in popularity however TTL logic is still manufactured and is quite common MOSFET operation resembles that of the JFETs studied previously As shown schematically in Fig 10 7 in an N channel MOSFET a positive 134 Hands on electronics Metal Oxide Semiconductor Substrate Fig 10 7 Schematic representation of an enhancement mode N channel MOSFET gate source voltage attracts current carriers into the channel between the drain and source allowing current to flow A gate source voltage near zero or negative closes the channel and prevents
105. dent projects To this end Chapter 6 Transistors III has been designed so that no subsequent experiment depends on it obviously this is also the case for Chapter 13 Digital lt analog conversion which has no subsequent experiment As you work through the exercises you will find focus questions and detailed instructions indicated by the symbol gt Key concepts for each exercise will be denoted by the symbol e Finally the standard system of units for electronics is the MKS system Although you may occasionally run across other unit systems we adhere strictly to the MKS standard 1 Equipment familiarization multimeter breadboard and oscilloscope In this chapter you will become acquainted with the workhorses of elec tronics testing and prototyping multimeters breadboards and oscillo scopes You will find these to be indispensable aids both in learning about and in doing electronics Apparatus required One dual trace oscilloscope one powered breadboard one digital multi meter two 10X attenuating scope probes red and black banana leads two alligator clips 1 1 Multimeter You are probably already familiar with multimeters They allow measure ment of voltage current and resistance Just as with wristwatches and clocks in recent years digital meters commonly abbreviated to DMM for digital multimeter or DVM for digital voltmeter have superseded the ana log meters that were used for
106. e Also there are restrictions on fanout the number of inputs that an output can drive which matter when actually designing circuits For example one LS TTL output can drive twenty LS TTL inputs but only four S TTL inputs In what follows we use 7400 generically to 128 Hands on electronics Table 10 1 Common families within the 7400 series Family Year Brief description TTL 1968 bipolar transistor transistor logic S 1974 TTL with Schottky transistors LS 1976 low power Schottky TTL ALS 1979 advanced low power Schottky F 1983 fast TTL HC 1975 high speed CMOS HCT 1975 high speed CMOS TTL compatible AC 1985 advanced CMOS ACT 1985 advanced CMOS TTL compatible LVC 1993 low voltage CMOS AHC 1996 advanced high speed CMOS refer to chips from any of these families Unless otherwise specified the chip families you actually use will depend on what happens to be on hand in the laboratory or if you are working through this book on your own on what you happen to find available Part numbers The original TTL chips were the 7400 series and the corresponding Mil Spec military specification 5400 series these became popular in the 1970s TTL chips are labeled with part numbers that begin with a letter code such as SN that is typically different for each manufacturer see Fig 10 2 then comes the 7 that identifies the device as belonging to the 7400 series then there may be a letter code that identif
107. e and collector resistors gt What is your transistor s saturation voltage Vcg sat What is the on voltage across the LED gt Approximately what minimum value of 6 must the transistor have to be sure of saturating when 5 V is applied at the input gt Drive the switch from the TTL output of the function generator digital square wave with a low voltage level near zero and a high level near 5 V at 100 kHz and use the dual trace oscilloscope to measure the turn on and turn off delays in nanoseconds Trigger the scope with the function generator while looking at both the function generator signal and the collector voltage The relatively slow turn on and turn off delays of the saturated switch are due to the charge stored in the base when the transistor saturates It takes time for the transistor to switch states since this saturation charge must flow in or out of the base through the input resistor High speed switching transistors such as the 2N2369 are manufactured to minimize this effect and can operate at frequencies as high as 1400 MHz 4 3 Additional exercises The following optional exercises offer additional practice 4 3 1 Darlington connection To provide high input impedance and reduce the input base current one can cascade two transistors in series i e buffer the input with an emitter follower stage This Darlington transistor pair acts like a single transistor whose current gain is the pr
108. e data sheet the 741 actually has on its single silicon crystal a multiple stage two input DC amplifier consisting of twenty transistors eleven resistors and one capacitor Its output voltage is proportional to the voltage difference between the two inputs i e it is a differential amplifier A differential amplifier is convenient when one wants to study the difference between two almost identical signals as well as in many other applications as we shall see Of course this is not to be confused with a differentiator Recall that a differentiator outputs the time derivative of its input signal not at all what a differential amplifier does 7 1 1 741 pinout and power connections Fig 7 1 shows the layout of the eight pin DIP package The package is a rectangular piece of black plastic containing the silicon chip itself as well as the fine gold wires that connect the chip to the contact pins Look at the top face of the package and orient yourself as to which pin is pin 1 looking at the top you see the pins bending away from you and the pin numbers increasing in the counterclockwise direction The end at which pin 1 is located is indicated by a special mark depending on the manufacturer not necessarily the mark shown in Fig 7 1 Pins 1 4 are located along one long edge of the package while pins 5 8 are on the opposite edge 1 Nowadays of course this is nothing for example the Pentium chip had 3 3 million transisto
109. e gain unity but the DC offset is small the constant current due to Q creates a constant voltage drop across R Fur thermore since the gate of Q is at the same voltage as the bottom of Ro to the extent that the two FETs and the two resistors match this should also be true for Q and R Thus the output voltage must follow the source voltage of Q1 gt Explain the operation of this circuit in your own words gt What are Ip Vos1 and Vos2 73 5 Transistors Il FETs 15 15 Fig 5 7 Source follower with current source load Fig 5 8 JFET amplifier The offset can be much improved by using a matched FET pair e g the 2N3958 dual JFET Such a circuit is often used in the input stage of an oscilloscope 5 2 4 JFET amplifier Construct the amplifier shown in Fig 5 8 The principle at work is essen tially the same as for the common emitter amplifier a varying input voltage controls a varying current which the drain resistor converts to an output voltage gt Using the common source curves that you measured in section 5 2 1 predict the quiescent gate source bias voltage and output voltage for this 74 Hands on electronics amplifier Power the amplifier and compare the measured values with your predictions gt How much power is dissipated by the FET gt What is the input impedance gt Is this an inverting or noninverting amp Explain why The voltage gain A is defined as the ratio of t
110. e recorded and processed as well as how computers are used in laboratory research and process control The process of converting digital information into voltages or currents whose magnitudes are proportional to the digitally encoded numbers is called digital to analog D A conversion The reverse process is called analog to digital A D conversion The devices that carry out these conversions are called DACs and ADCs respectively In this chapter after building a simple DAC from a digital counter and an op amp you will continue your exploration of analog digital conversion by building a 4 bit tracking ADC Having learned the basic operating princi ples you ll use an ADCO80x 8 bit successive approximation A D chip to digitize i e convert to digital an arbitrary AC signal The original signal will then be re created from the digitized data using a DACO80x D A chip This exercise will also allow you to explore the limitations of ADC and DAC operations Please be sure to work through these circuits in advance otherwise it is highly unlikely that you will successfully complete the exercises in a timely fashion Carefully study the manufacturer s data sheets which pro vide extensive details on operation and performance As always complete schematic diagrams significantly improve debugging efficiency Apparatus required 167 Breadboard oscilloscope 74191 TIL311 311 comparator 741 op amp resistors capacitors DAC0806 or similar
111. e rising edge of the clock signal causes the output to change while the falling edge of the clock signal has no effect on the flip flop are shown as either high or low we tend not to worry in timing dia grams about analog details such as the exact voltage to which high and low correspond Fig 11 1 defines several important terms The time between a clock edge and the resulting changing edge of the output is defined as the propagation delay tpp Note how the time is measured from the midpoint between logic low and high The setup time tsy is the minimum time that an input signal must be stable preceding a clock edge The hold time ty specifies the minimum time that the input signal must be stable following a clock edge The transition time measures the time required for a signal to transition from logic low to high tr_y or from logic high to low fryr These timing parameters are specified in the data sheets Manufacturers guarantee that the IC will perform correctly if the user satisfies the specified minimum values The specs are usually worst case values For example the measured propagation delay is almost always less than the maximum value specified by the manufacturer Although manufacturers often specify the typical propagation delay as well it is not guaranteed safe designers heed the minima and maxima not the typicals 11 2 Flip flop basics 11 2 1 Simple RS latch The circuit shown in Fig 11 2 is the simples
112. ection ratio by measuring both the common mode volt age gain and the differential voltage gain The common mode voltage gain is determined by applying identical sig nals to both inputs and observing the output voltage Acm Voutoy Vincu Using a 1 kHz sine wave at maximum amplitude as your input tune your dif ference amp to minimize the output amplitude i e adjust the potentiometer until the output amplitude is as small as possible The best estimate for the common mode gain can be made using the averaging feature from the 97 7 Introduction to op amps ACQUIRE menu of the TDS210 oscilloscope It may be possible depend ing on the quality of your op amp to tune the potentiometer such that no output signal is visible even at the most sensitive scale gt Verify that R R R3 R4 gt Estimate or set an upper limit on the common mode voltage gain The resistance ratios can be measured using your meter however be sure to turn off the power and disconnect each component before making your measurements accurate resistance measurements cannot be guaran teed if the component remains connected to the circuit since then you are measuring a parallel combination with the other components rather than just the resistance of interest For example when measuring the resistances between the potentiometer center tap and ends be sure to disconnect all wires connecting the pot to the input signal op amp and ground Replace all resis
113. ed as a noninverting amplifier Again neglecting the tiny input currents of the op amp and assuming infinite open loop gain application of Ohm s law shows that the closed loop voltage gain of this circuit is TR hR Ry A 7 6 LR R eo As above Eq 7 6 follows from the assumptions that all of the current flows around the op amp and that feedback forces the inverting input to follow the signal applied to the noninverting input So if R 10 k a gain of 11 can be achieved by choosing R 100k while a gain of 2 results from choosing R 10k Vout Fig 7 3 Op amp noninverting amplifier circuit 90 Hands on electronics 7 1 4 Op amp golden rules We see from the above that to understand to a reasonable approximation an op amp circuit with negative feedback you need only two simple rules 1 The inputs draw no current 2 The output does whatever is necessary to maintain the two inputs at equal voltages 7 1 5 The nonideal op amp Although the ideal op amp approximations are very close to reality in most situations here are a few limitations that you should consider Input offset voltage A small DC output voltage usually results even when the inputs are iden tical The input offset voltage refers to the DC voltage that must be ap plied at the input to achieve exactly zero volts at the output The nonzero offset arises due to manufacturing limitations however most op amps have pins that allow f
114. ed in a spark to a MOSFET it is sometimes sufficient to blast a hole 136 Hands on electronics SS cc cc P channel MOSFET S sS P channel MOSFET Irr rro e a e Be KS A L L H H C N channel 330 MOSFET A LED N channel MOSFET Fig 10 9 Schematic representation of a CMOS NAND gate with LED logic level indicator through the oxide layer destroying the MOSFET You ve probably heard of static sensitive electronics such as computer memory cards These cards are constructed using MOSFETs To minimize the accidental destruction of components we ve chosen medium power MOSFETS for this lab these are much more robust and less sensitive to static than the tiny high speed MOSFETS used inside high density chips 10 2 4 Powering TTL and TTL compatible integrated circuits Unlike the 741 and 311 chips that you ve used previously the logic chips to be used here will require only a single 5 V supply rather than separate positive and negative supplies As in the case of the 741 the actual power connections are often omitted in schematic diagrams but you must not forget to make those connections Note that not all chips have the same number of pins furthermore even among chips with the same number of pins not all follow the same convention in power supply connections You must look up the pinout of each chip you employ 137 10 Combinational logic Be careful Note that TTL and CMOS ICs are
115. ed op amp inverting amplifier circuit Ry op amp V Su Fig 8 2 Basic op amp differentiator in the time domain to an arbitrary input waveform Then we can analyze the circuit using Ohm s law Since to an excellent approximation J J the gain is determined by the current voltage characteristics of the input and feedback devices as we will see in more detail below 8 1 1 Differentiator As shown in the circuit of Fig 8 2 the basic op amp differentiator not to be confused with the difference amplifier is similar to the basic inverting amplifier studied in Chapter 7 except that the input element is a capacitor rather than a resistor Using the assumption that the output does whatever necessary to maintain the two inputs at equal voltages it is easy to show that the output voltage is given by d dV Vent TRe E dt dt 8 2 since Q C Vin where Q is the charge stored on the capacitor 103 8 More op amp applications Rg Op amp Vout Fig 8 3 Improved op amp differentiator One problem with the basic circuit is that the capacitor s reactance 1 Xc decreases with increasing frequency Since here Zi Xc Eq 8 1 shows that the output voltage of the basic differentiator increases with frequency making the circuit susceptible to high frequency noise and prone to oscillation A more practical differentiator circuit is shown in Fig 8 3 with a resistor placed in series with the input capacitor to lim
116. ed to sound for a specified duration using two 555s by combining the timer from Fig 9 6 b with the alarm circuit Connect the alarm s RESET input to the timer s output line Trigger the timer and the alarm will sound for the duration of the timer s output signal 10k Vec Discharge 10k 1 k pot volume control Speaker Fig 9 7 555 timer configured as an alarm 122 Hands on electronics You can also make a pulsing alarm by using two oscillators The first should oscillate with a period of a few seconds The output of this oscillator is then connected to the RESET line of the second oscillator The second oscillator s output is connected to the speaker and can oscillate with any audio frequency of your choice 9 2 2 Sine cosine oscillator Perhaps surprisingly the sine wave is one of the most difficult waveforms to produce As you saw when you differentiated the sine output of the PB 503 s built in function generator the PB 503 uses a piecewise linear approximation to a sine function The circuit of Fig 9 8 should produce a better approximation It should oscillate at 1 2x RC as long as R lt R So you don t expect it to work with R 10k unless Eq 9 5 happens to be satisfied due to resistor manufacturing tolerances You can vary R so as to satisfy Eq 9 5 by using the 10 k pot for R or by f 9 5 adding other resistors in parallel with the 10 k Set up the circuit and apply power Once
117. el 1 You should see that the op amp output signal is a square wave that is 90 out of phase with the input i e the output signal is a representation of the negative of the time derivative of the input gt Measure the step height in volts of the square wave output of the op amp The theoretical prediction is Vin tep height 2R C step heig Cl 8 15 Now change the input frequency from 500 Hz to 10 kHz Be sure to reduce the input amplitude to avoid saturating the output voltage Record the appearance of the output signal at this frequency Measure the peak to peak output voltage and determine the voltage gain gt Sketch the input and output waveforms at 500 Hz and 10 kHz and com ment on your results gt Compare your data with Eq 8 15 and compare the measured gain at 10 kHz with the theoretical expectation gt At what approximate frequency does this circuit cease to act as a differ entiator i e approach the operation of an inverting amplifier Set up the circuit shown in Fig 8 5 with R R 10k R 100k and C 0 0047 pF Adjust the peak to peak voltage of the square wave input to 1 V and the frequency to 10 kHz You should see an output signal that is a triangle wave 90 out of phase with the input square wave gt Derive Eq 8 6 gt Measure the peak to peak voltage of the triangle wave and compare with the value you would expect theoretically Now change the input frequency to 1
118. enin equivalent A way to model complex circuits based on Th venin s theorem which reduces most circuits to a single ideal voltage source in series with a single impedance time domain AC circuit analysis approach that focuses on circuit response to an arbitrary waveform vs time volt Unit of electrostatic potential 1 volt 1 V 1 joule coulomb voltage Electrostatic potential Voltage is defined and measured with respect to a common reference or ground point When multiplied by the value of the charge voltage gives the potential energy of the charge with respect to that reference Positive current flows from points of higher voltage to points of lower voltage from larger potential energy to lower potential energy Vcc Most positive voltage in a circuit Vee Most negative voltage in a circuit 199 Index B 48 50 hpg 48 50 Q 124 TBE 53 57 Te 52 57 Ve 50 52 Vcp 50 Vcg 51 3 dB point 26 2N3904 pinout 54 2N3906 pinout 54 2N5485 pinout 69 311 comparator 114 311 pinout 114 555 timer 118 156 7400 IC series 125 741 op amp 85 741 pinout 86 74121 monostable 156 159 74121 pinout 159 74138 decoder 178 74150 mux 162 74150 pinout 162 74191 counter 168 7489 RAM 163 7489 pinout 163 AC coupling 43 acceptor 32 active bandpass filter 123 active differentiator 102 106 active filter 123 active integrator 103 107 active rectifier 108 ADC 167 successive approximation 171
119. erage DC voltage across it as measured with a voltmeter Using these assumptions and the fundamental capacitor equation Q CV gt Calculate the output voltage droop in each cycle and compare with the peak to peak ripple voltage as measured Is the observed percentage discrepancy within the tolerances of your components Explain gt Replace the 100 uF electrolytic capacitor with a 1000 uF capacitor Do you expect the ripple voltage to increase or decrease Explain gt Measure the ripple voltage and compare with your expectations Full wave rectification should decrease the ripple by about a factor of two This can be accomplished using two diodes and the transformer s center tap or by using a diode bridge Diode bridge rectifiers are available as a single encapsulated unit making the bridge rectifier approach partic ularly convenient These bridges have four diodes within The terminals are labeled marks the two terminals that should be connected to the transformer secondary and and denote the positive and negative outputs see Fig 3 9 Diode Bridge Fig 3 9 An example of how to insert a diode bridge into a breadboard 44 Hands on electronics Transformer Diode Bridge fuse 120 VAC Fig 3 10 Full wave rectification using a diode bridge Caution A defective bridge element can blow the power transformer fuse check it be fore placing it in service It should show essentially
120. ercise will deliberately lead to the destruction of a carbon film resistor 2 2 1 Destructive demonstration of resistor power rating Caution In the following exercise care must be taken to prevent burns The resistor in the following exercise will become very hot and may even catch fire briefly Keep the body of the resistor well above the breadboard Do not touch the resistor with your fingers Remove the destroyed resistor using pliers or a similar tool Be sure that the power is turned off and construct the circuit shown in Fig 2 2 using a 1 watt carbon film resistor gt Turn on the power and observe the effect on the resistor Be sure to turn off the power as soon as the resistor begins to smoke Record your observations and comments 68 Q 1 4 watt Resistor 15V Fig 2 2 This circuit can be used to demonstrate destructive power loading Note that the resistor will heat up rapidly 22 Hands on electronics gt Calculate the power that was dissipated by the resistor before it burned out What is the minimum resistor value that can be safely used in this circuit Assume that only 1 watt resistors are available gt Calculate the current that flowed through the resistor before it burned out Note that even though the voltage was low and the current was well under 1 A damage was nevertheless done Because your body s resistance is large low voltages can t give you a shock but in the wrong circumstances
121. erface two pieces of equipment that may not have been designed for that purpose To that end our goal is that by the end of the book you will be able to design and build any little analog or digital circuit you may find useful or at least understand it well enough to have an intelligent conversation about the problem with an electrical engineer A basic knowledge of electronics will also help you to understand and appreciate the quirks and limitations of instruments you will be using in research testing development or process control settings We expect few of you to have much familiarity with such physical theo ries as electromagnetism or quantum mechanics so the thrust of this course will be from phenomena and instruments toward theory not the other way round If your curiosity is aroused concerning theoretical explanations so much the better but unfamiliarity with physical theory should not prevent you from building or using electronic circuits and instruments xviii Acknowledgments We are grateful to Profs Carlo Segre and Tim Morrison for their contri butions and assistance and especially to the IIT students without whom this book would never have been possible Finally we thank our wives and children for their support and patience It is to them that we dedicate this book xix Introduction This book started life as the laboratory manual for the course Physics 300 Instrumentation Laboratory offered every semester
122. es in the output waveform gt How does the output signal from the 311 differ from that of an op amp What is the 311 s slew rate 9 1 2 Unintentional feedback oscillation An unfortunate side effect of the 311 s fast response is its tendency to oscillate when presented with a sufficiently small voltage difference be tween its inputs The unavoidable capacitive coupling typically a few picofarads depending on how the circuit is wired between the output and the input causes some feedback so when the output switches state a small transient signal is picked up at the input There is also some feedback due to the changing input base current when one input transistor switches on and the other switches off These effects can result in self sustaining oscillation The pickup occurs through what is essentially a voltage divider con sisting of the large coupling impedance i e small capacitance between the output and the input together with whatever impedance to ground is present at the input The effect is thus mitigated if there is a low impedance to ground at the input and exacerbated if the impedance is high Try to make your 311 oscillate by feeding it a triangle wave with a gentle slope dV dt i e small amplitude and or low frequency Use V 15 V and V_ ground To exacerbate the feedback insert 10 k in series with the function generator source resistance as shown in Fig 9 2 When looking at the input signal it is a goo
123. esistance as a function of gate voltage Timing diagram with timing definitions for a rising edge triggered flip flop 102 103 104 104 105 105 109 110 111 114 115 116 118 119 120 121 122 123 127 129 130 131 132 132 134 135 136 137 138 145 xiv 11 2 11 3 11 4 11 5 11 6 11 7 11 8 11 9 12 1 12 2 12 3 12 4 12 5 12 6 12 7 13 1 13 2 13 3 13 4 13 5 13 6 13 7 C 1 C 2 List of figures Simple RS latch made of two input NANDs with state table 7474 D type flip flop with state table Sample timing diagram for a positive edge triggered 7474 D type flip flop Pinout of the 74112 JK flip flop Pinout and power connections for the 74373 and input and output connections for testing the tri state output Divide by four ripple counter Synchronous divide by four counter Looking at contact bounce by driving a divide by four counter from a switch Pinout of 7490 decade counter Pinout of TIL311 hex display Timing diagram for a gated clock signal Pinout of 121 and 123 one shots with external RC timing network Substandard outputs resulting from gating clock signals Pinout of 74150 16 to 1 multiplexer Pinout of 7489 16x4 RAM Simple D A converter and output waveform resulting from input counting sequence Simple A D converter Pinout for ADC080x series of A D converters and the on chip self clocking configuration Pinout for DACO80x series of D A chips M
124. ethod for producing a DC shifted waveform Control logic for 8 bit successive approximation ADC 8 bit successive approximation ADC Series RC circuit Right triangle to illustrate Eq C 17 146 147 147 149 150 151 152 153 157 158 160 160 161 163 163 168 171 172 175 176 179 180 193 193 1 1 1 2 2 1 3 1 4 1 10 1 XV Tables Digital multimeter inputs Color code for nonprecision resistors Some typical dielectric materials used in capacitors A sample of commercially available diodes A sample of commercially available bipolar transistors Common families within the 7400 series page 2 16 36 50 128 xvi About the authors Dr Daniel M Kaplan received his Ph D in Physics in 1979 from the State University of New York at Stony Brook His thesis experiment discovered the b quark and he has devoted much of his career to experimentation at the Fermi National Accelerator Laboratory on properties of particles containing heavy quarks He has taught electronics laboratory courses for non electrical engineering majors over a fifteen year period at Northern Illinois University and at Illinois Institute of Technology where he is cur rently Professor of Physics and Director of the Center for Accelerator and Particle Physics He also serves as Principal Investigator of the Illinois Consortium for Accelerator Research He has been interested in electronics since high school during the junior yea
125. flop unpredictable output 11 2 2 D type flip flop In practice RS latches are seldom used The most commonly used flip flop is the clocked D type which remembers the state of its D input at the time of a clock transition but is insensitive to D at all other times We will use the 7474 D type flip flop Fig 11 3 which is sensitive to rising clock edges low to high transitions in other words it is positive edge triggered Later in this chapter you will encounter a negative edge triggered JK flip flop Note that in addition to its fancy D and clock inputs the 74 retains the simple RESET and SET inputs of the RS latch which are active low since internally the 74 is constructed from NANDs gt Test the RESET and SET inputs and explain what they do then tie them to 5 V to make sure they are inactive Next check out the clocked operation of the 74 illustrated in Fig 11 4 Provide the clock signal using amomentary contact breadboard debounced push button and the D input using a breadboard logic switch and display 148 Hands on electronics the Q and Q outputs using logic indicators When using the debounced push buttons on the PB 503 be sure to add a pull up resistor as you did for the logic level switches see Fig 10 10 gt Show that information presented on the D input is ignored except during clock transitions by changing the state of
126. g the connec tions between the noninverting input the 100 Q resistor and the inverting input as short as possible long wires in this current path act as an antenna and pick up electromagnetic noise from the environment as you will soon observe 7 2 2 Inverting amplifier Now hook up the inverting amplifier of Fig 7 2 with R 10 k and R 100 k Using a 1 kHz sinusoidal input signal with an amplitude of approximately 1 V look at the input and output gt Verify that the amplifier inverts Measure the gain and compare with what you expect Replace the 100 k feedback resistor with 10 k what gain do you predict and observe now Put the 10 k resistor back for the following parts Due to feedback the output impedance of the inverting amplifier is extremely small the 75 Q open loop output impedance of the 741 is multiplied by the ratio of the closed loop gain to the open loop gain here a factor of order 1075 gt Confirm the small size of the closed loop output impedance by adding a 100 Q load to ground at the output To see that this gives sensitivity to the output impedance analyze the voltage divider circuit consisting of the output impedance in series with the load resistance gt Do you expect the output amplitude to decrease measurably under load How big a decrease do you predict Is this consistent with what you observe You will need to use a small input signal how small to avoid running into the 741
127. he circuit less sensitive to noise The phenomenon of hysteresis should be familiar from your study of magnetic materials in introductory physics In the present context the term 15 Fig 9 3 Schmitt trigger using 311 comparator 117 9 Comparators and oscillators hysteresis refers both to the situation of having two different comparator thresholds depending on the history of the input signal as well as to the size of the voltage difference between the two thresholds The threshold voltage at the noninverting terminal is found by applying the voltage divider equation R2 Vint Vout in t Ri ORS 9 1 There are two cases to consider since the output might be at 15 V or it might be at ground i e since Vout has two possible states Vin has two possible states gt Build the circuit and apply a signal with an amplitude of at least 1 5 volts Try to create output oscillations Notice the rapid and clean transitions at the output independent of the input waveform or frequency gt Sketch the output waveform Is the output symmetric If not why not To see exactly what is happening use the two channel oscilloscope to display the voltages at both comparator input terminals simultaneously Be sure to use DC coupling for both channels and set them to the same voltage sensitivity and the same zero offset gt Carefully sketch both input waveforms on the same graph and explain how the circuit wo
128. he counter will count up the number of clock pulses which is proportional to the duration of the pulse from the one shot Fig 12 4 shows the pinout of the 74121 and 74123 monostable multivi brators For the RC timing network use a conveniently sized resistor and capacitor the timing rules vary by family and type so be sure to refer to the correct data sheet for your one shot In brief the predicted output pulse width is given by In2RextCext 74121 ty 4 KRegCex 74LS8123 12 1 RextCext 74HC123 2 But the converse is not true TTL logic levels do not satisfy the CMOS input criteria 160 Hands on electronics Gated Clock Gate c ty Fig 12 3 Timing diagram for a gated clock signal Notice how the gated clock signal is simply the logical NAND of the gate and clock signals Trigger Fig 12 4 Pinout of 121 and 123 one shots with external RC timing network see the data sheets for details In the above equation K is a parameter specifed on the 74LS123 data sheet The output pulse begins following a rising edge at the trigger input The A and B inputs can be configured either to inhibit triggers or to produce a trigger from a rising B input or falling A inputs edge Depending on the specific chip used there are either one or two A inputs see Fig 12 4 There is always only one B input gt Design and build logic that produces a gated clock signal as shown in Fig 12 3 Be
129. he fundamental rule governing the behavior of capacitors is Q CV 2 1 where Q is the charge stored on the capacitor at a given time V is the voltage across the capacitor at that time and C is the capacitance Current can flow into or out of a capacitor but only to the extent that the charge on the capacitor is changing In other words the current into or out of a capacitor is equal to the time derivative of the charge stored on it You can see the resemblance between Eq 2 1 and Ohm s law Eq 1 1 The key difference is that for a resistor it is the time derivative of the charge that is proportional to voltage whereas for a capacitor it is the charge itself Capacitors are thus useful only in circuits in which voltages or currents are changing in time namely AC circuits We will consider the response of circuits to periodic waveforms these can be characterized by their frequency f and period T which of course are related by T 1 f as well as their angular frequency w 27x f If f is expressed in hertz cycles per second then T is in seconds and w is in radians per second A periodic waveform is also characterized by its amplitude which assuming the wave is pure AC i e symmetric with respect to ground is the maximum voltage that it reaches There are an infinite variety of AC waveforms but to understand how capacitors are used it is sufficient to focus on two square waves and sine waves You have already encounte
130. he output amplitude to the input amplitude If the source voltage remains fixed then AVg AVgs As discussed previously 8m Alp AVes and since AVp Alp Rp A 8m Rp gt What is the predicted voltage gain for this amplifier Using a 1 kHz small amplitude sine wave input measure the voltage gain and compare with the expected gain The source capacitor is used to fix the source voltage even as the drain current fluctuates due to the AC input This trick can also be used to in crease the voltage gain of the bipolar transistor common emitter amplifier This implies that the gain will be frequency dependent gt Switch the input to a triangle wave and adjust the frequency widely Ex plain what you see Replace the source capacitor with a 100 uF capacitor How does this change things gt Try several different 2N5485s and record the voltage gain and quiescent drain current and output voltage How reproducible are the results gt Comment on the design and operation of simple transistor and JFET circuits For example when would you choose a bipolar transistor over a JFET or vice versa Feel free to include any general comments you have on the experience you ve gained from the last few chapters ee 6 Transistors Ill differential amplifier In this chapter we will study the transistor differential amplifier circuit This is a very important transistor circuit as it is the basis of the operational amplifier or
131. here are an enormous number of ways that op amps can be applied to process analog signals In this chapter we will explore several such ap plications circuits that differentiate or integrate their input voltage as a function of time form the logarithm or exponential of their input voltage or rectify their input voltage The op amp versions of these applications come closer to the ideal than the passive versions of some of them that you studied in earlier chapters We will also see how to use feedback to compensate for the limitations of discrete devices Apparatus required Breadboard dual trace oscilloscope with two attenuating probes one 741C and one LF411 operational amplifier one 1 k two 10 k and one 100 k 1 W resistor 0 0047 F and 0 033 uF capacitors two 1N914 or similar silicon signal diodes 2N3904 and 2N3906 transistors 8 1 Op amp signal processing 101 Recall that for an inverting amplifier made from an op amp with input resistor R and feedback resistor Rp the gain is R R neglecting the input offset voltage and offset and bias currents and taking the op amp open loop gain to be infinite We can generalize this result for devices other than resistors as illustrated in Fig 8 1 Zr Ay Zi 8 1 Eq 8 1 is useful if we are analyzing circuit performance in the frequency domain for a sine wave input but often we are concerned with the response 102 Hands on electronics Vout Fig 8 1 Generaliz
132. hook or grabber An attenuating scope probe can distort a signal The manufacturer there fore provides a compensation adjustment screw which needs to be tuned for minimum distortion The screw is usually located on the assembly that connects the probe to the scope or occasionally on the tip assembly gt Display the calibrator square wave signal on the scope If the signal looks distorted i e not square carefully adjust the probe compensation using a small screwdriver If you have trouble achieving a stable display try AUTOSET gt Check your other probe Make sure that both probes work are prop erly compensated and have equal calibrations Sketch the observed waveform Consult your oscilloscope user manual for more information about car rying out a probe test Note that each probe also has an alligator clip sometimes referred to as the reference lead or ground clip This connects to the shield of the coaxial cable It is useful for reducing noise when looking at high frequency 11 1 Equipment familiarization time intervals of order nanoseconds or low voltage signals Since it is connected directly to the scope s case which is grounded via the third prong of the AC power plug it must never be allowed to touch a point in a circuit other than ground Otherwise you will create a short circuit by connecting multiple points to ground which could damage circuit components This is no troub
133. how the meter is connected in parallel with the resistor a Potentiometer Slider b Power Supply Center Tap Multimeter Ground Common Ii Fig 1 3 Measuring current a Schematic diagram of series circuit consisting of power supply 10 k potentiometer and multimeter Note that the center tap of the potentiometer is left unconnected in this exercise accidentally connecting it to power or ground could lead to excessive current flow and burn out the pot b A drawing of the same circuit showing how the DMM leads should be configured to measure current Note that the meter is connected in series with the resistor 1 2 2 Measuring current resistance and Ohm s law Current is measured by connecting a current meter an ammeter ora DMM in its current mode in series with the circuit element through which the current flows see Fig 1 3 Note carefully the differences between Fig 1 2 and Fig 1 3 Hands on electronics Recall that Ohm s law relates current J voltage V and resistance R according to V IR 1 1 This is not a universal law of electrical conduction so much as a statement that there exist certain materials for which current is linearly proportional to voltage Materials with such a linear relationship are used to fabricate resistors objects with a known and stable resistance Usually they are little cylinders of carbon carbon fi
134. hy one is better than the other gt Sketch Vin Vout and the op amp output for both half wave rectifier circuits at 100 Hz and at 10 kHz gt How is this active rectifier better than a simple diode rectifier For example what would be the response of a simple rectifier to an input signal of amplitude less than 0 7 V How does this circuit respond to such a signal gt Comment on the performance of the LF411 as compared with that of the 741 8 2 4 Op amp with push pull power driver A typical op amp such as the 741 by itself does not have enough output current capability to drive an 8 Q load such as a speaker The addition of a push pull driver stage to buffer the output is a common solution When large output power is needed several watts as in audio applications power Darlingtons are often employed as the push pull transistors Recall that in a previous chapter you used a push pull power driver to drive the breadboard s speaker from the function generator This circuit displayed crossover distortion since one transistor switched off 2 Vgg before the other switched on One solution to crossover distortion is to employ an 110 Hands on electronics a 5 2N3904 Speaker 2N3906 5 Fig 8 9 Op amp follower with push pull output buffer power driver with two feedback arrangements a feedback before and b feedback after power driver op amp to compare the output signal with the input signal and cor
135. ial 143 synchronous 144 logic function universal 140 logic levels 125 126 TTL 126 logic level displays 137 low logic level 126 machine state 143 162 magnitude comparator 142 margin noise 126 memory random access 162 word addressable 163 meter digital 1 mho 48 MKS 16 momentary contact switch 153 monostable 156 159 monostable 74121 156 159 monostable multivibrator 156 159 MOSFET 65 MOSFET logic 133 multimeter 1 multimeter diode test 54 multiplexer 162 multiplexer logic 162 multivibrator 120 143 156 159 astable 120 156 bistable 143 156 monostable 156 159 mux 162 NAND 140 NAND gate 140 negative feedback 75 79 88 negative logic 127 negative edge triggered counter 157 negative edge triggering 147 149 157 noise margin 126 noninverting amplifier op amp 89 NPN transistor 48 offset voltage 78 Ohm s law 6 one logic level 126 one shot 156 159 op amp 79 85 differentiator 102 golden rules 90 ideal 87 integrator 103 inverting amplifier 88 noninverting amplifier 89 rectifier 108 signal processing 101 op amp inverting amplifier 168 open collector output 164 open loop 88 91 113 operational amplifier see op amp OR 142 OR gate 142 oscillation 115 parasitic 56 oscillator square wave 117 relaxation 117 sine cosine 122 oscilloscope 8 10 cursors 14 measurement 13 triggering 12 output impedance 45 measurement of 46
136. ial charging discharging equation and e as an AC voltage divider Both approaches are valid in fact they are mathematically equivalent but the first is more useful when using capacitors as integrators or differ entiators whereas the second is more useful when analyzing low pass and high pass filters The first is referred to as the time domain approach since it considers the voltage across the capacitor as a function of time and the second as the frequency domain approach since it focuses on the filter attenuation vs frequency Apparatus required Oscilloscope digital multimeter breadboard 68 Q and 10 KQ resistors 0 01 uF ceramic capacitor 2 1 Review of capacitors 15 As you may recall from an introductory physics course a capacitor consists of two parallel conductors separated by an insulating gap The capacitance 16 Hands on electronics Table 2 1 Some typical dielectric materials used in capacitors Material Dielectric constant Vacuum 1 0 Air at STP 1 00054 Paper 3 5 Mica 5 4 Ceramic 100 C is proportional to the area of the conductors A and inversely propor tional to their separation s multiplied by the dielectric constant xK of the insulating material C KkeA s where in the MKS system of units A is in meters squared s in meters and C in farads abbreviated F 1 farad 1 coulomb per volt The constant of proportionality is the so called permittivity of free space a
137. idal signal from the function generator to the pot in place of the 10 V DC gt Look at the function generator s output signal with the scope and measure its peak to peak voltage amplitude and r m s voltage The scope s MEASURE menu is useful here Look at the signal at the pot s center tap what are the peak to peak amplitude and r m s values there How does the pot s voltage division ratio R2 R R2 compare for DC and AC 2 The 10 k pot is located near the center of the bottom edge of the PB 503 breadboard and is adjusted by means of a large black knob If you don t have a PB 503 find a 10 k pot on your breadboard if it has one otherwise you will have to use a separate 10 k pot 24 Hands on electronics ae lit S a Fig 2 4 The voltage divider concept works perfectly well for RC circuits This circuit is also known as a low pass filter or as a voltage integrator 2 4 RC circuit Now hook up a 10 k resistor and a 0 01 uF ceramic capacitor in series Ground one end of the capacitor connect the other end to the resistor and connect the other end of the resistor to a 500 Hz square wave from the function generator see Fig 2 4 Display the input signal output of the function generator on channel 1 of the scope and the output signal at the junction of the resistor and capacitor on channel 2 gt What are the amplitudes of the input and output waveforms gt Sketch the output waveform You ma
138. ies the family then the number that identifies the particular device e g 00 for a quad NAND gate 01 for quad NAND with open collector outputs 02 for quad NOR gate 74 for dual D type flip flop etc and finally there may be letters that indicate package style reliability degree of testing by the manufacturer etc For example the MC74LSOOND is a Motorola LS TTL quad NAND gate in the plastic dual in line package with 160 hour burn in testing Pinouts and data sheets Data sheets are available on the web or in data books produced by the chip manufacturer The sheets specify the function of each pin of the IC package and provide detailed data on chip performance In general 7400 series chips have compatible pinouts independent of the family For example the 129 10 Combinational logic Pin 14 Pin 8 1A Vcc 1B 4B 1Y 4A 2A 4Y 2B 3B 2Y 3A Series GND 3Y Manufacturer Family Chip Type Fig 10 2 Labeling of 7400 series chips pinout for a 74HC00 quad NAND IC is the same as the pinout for the 74LS00 quad NAND IC It is always a good idea to review the data sheet before using any logic chip Another consistency is in the pin numbering scheme If you orient the chip so that the pins are bending away from you and the end that has a notch or a dot is pointing to the left pin 1 is the one at the lower left of the package The numbering then proceeds sequentially around the chip in a counterclockwise direction such that the
139. ifier 75 76 86 differential gain 76 77 differential signal 75 differentiator 15 27 75 102 active 102 106 op amp 102 106 digital 167 digital information 167 digital logic 125 debugging 144 digital meter 1 digital recording 177 digital to analog conversion 167 digital to analog converter 167 diode 31 gate channel 66 light emitting 60 zener 123 diode characteristic 31 33 34 diode constant n 106 diode drop 37 diode logic 131 diode test multimeter 54 diode bridge rectifier 43 DIP IC package pin numbers 129 201 Index display logic level 137 TIL311 158 distortion 58 crossover 63 109 divide by four circuit 151 divide by ten circuit 158 divide by two circuit 148 DMM 1 donor 32 driver push pull 109 DVM 1 dynamic resistance 37 52 57 of diode 37 of emitter 52 FET source 72 Ebers Moll transistor model 52 ECL 125 electrolytic 16 electrolytic capacitor 16 emitter 48 emitter follower 55 emitter resistance 52 equality tester 141 exclusive OR gate 141 exponential amplifier 105 factor quality Q 124 false 126 feedback 79 negative 71 75 79 88 117 positive 62 113 117 FET 65 FET current source 70 FET saturation 67 filter 123 active 123 bandpass 123 high pass 15 28 low pass 15 25 28 finite state machine 143 162 flip flop 143 156 D type 147 JK 148 toggling 148 follower voltage 94 forward bias 34 four bit coun
140. iggles on the output signal you can verify that they are real as opposed to noise using the signal averaging feature of the scope s ACQUIRE menu You ve discovered a poorly kept secret of function generator design The sine waveform is rather difficult to generate and most function generators actually use an approximation to it that is piecewise linear around the peaks and valleys The derivative of a piecewise linear function is a series of steps and plateaus 2 8 High pass filter gt What attenuation and phase shift do you observe with a 50 Hz sine wave as input gt What about with a 50 kHz sine wave gt Why do these phase shifts make sense gt Should the breakpoint frequency be any different in this configuration than in the low pass filter Check it and make sure Compare your mea surements with R Vout Vi z 2 28 R a gt 2 29 JR X RC K 2 30 Vin J1 FORC gt Show that well below the breakpoint frequency Eq 2 30 predicts that the output amplitude should increase linearly with frequency Take a few measurements to demonstrate that this prediction is correct 2 9 Summary of high and low pass filters For reference here once again are the key equations describing high pass and low pass RC filter operation in the frequency domain High pass Vout wRC 2 31 Vin 6 1 RC 2 1 od arctan 2 32 oR 29 2 RC circuits Low pass Vou 1 ou 2 33 Vin V1 RC arc
141. iments 9 1 1 Op amp as comparator 9 1 2 Unintentional feedback oscillation 9 1 3 Intentional positive feedback Schmitt trigger 9 1 4 RC relaxation oscillator 9 1 5 555 timer IC 9 2 Additional experiments 9 2 1 Alarm 9 2 2 Sine cosine oscillator 9 2 3 Active bandpass filter 91 91 92 93 94 95 97 97 98 101 101 102 103 105 106 106 108 108 109 111 113 113 113 115 116 117 118 121 121 122 123 IX 3 10 11 Contents Combinational logic 10 1 Digital logic basics 10 1 1 Logic levels 10 1 2 Logic families and history 10 1 3 Logic gates 10 1 4 Summary of Boolean algebra 10 2 CMOS and TTL compared 10 2 1 Diode logic 10 2 2 Transistor transistor logic TTL 10 2 3 Complementary MOSFET logic CMOS 10 2 4 Powering TTL and TTL compatible integrated circuits 10 3 Experiments 10 3 1 LED logic indicators and level switches 10 3 2 MOSFETs 10 3 3 CMOS NAND gate 10 3 4 Using NANDs to implement other logic functions 10 3 5 TTL quad XOR gate 10 4 Additional exercises 10 4 1 7485 4 bit magnitude comparator Flip flops saving a logic state 11 1 General comments 11 1 1 Schematics 11 1 2 Breadboard layout 11 1 3 Synchronous logic 11 1 4 Timing diagrams 11 2 Flip flop basics 11 2 1 Simple RS latch 11 2 2 D type flip flop 11 3 JK flip flop 11 4 Tri state outputs 125 125 126 127 129 130 131 131 132 133 136 137 137 138 140 140 141 142 142 143 144 144 144 144 144 145 1
142. in 1 to 5 V and drive pin 2 from the TTL output of the function generator Measure the output rise and fall times and propagation delay of the 74HCO00 Compare with the values listed on the 74HC00 data sheet For measurements of propagation delay it is useful to define the transition times of the input and output signals as the times at which they cross 2 5 V which is about half way between high and low A good technique for precise timing of logic signals is to set both scope channels to 1 or 2 V division and use the scope s vertical position knobs to put ground 2 5 V below the center of the graticule then you can easily measure the time at which each signal crosses 2 5 V 10 3 4 Using NANDs to implement other logic functions As mentioned above NANDs are a universal logic function in the sense that any Boolean logic function can be constructed from them the same 141 10 Combinational logic is true of NOR and XOR In the early days of logic chips only NAND was available since AND and OR functions require more transistors to implement gt Construct the following two input logic circuits using only NAND gates AND OR NOR To figure out the necessary logic you can make use of DeMorgan s the orems Eqs 10 1 and 10 2 Recall that you can use a NAND gate as an inverter if needed just connect the two inputs together or tie one input high gt Write down your schematic diagram for each circuit indicating pin num
143. inevitably due to the proximity of the leads to each other rather than by design If you re curious about this try omitting the base resistor and see what happens Not all 2N3904s are guaranteed to oscillate in this circuit whether yours does could also depend on details of the wiring arrangement gt Measure the input impedance To do so replace the base resistor with 10k and measure the small decrease in amplitude from one side of Rg to the other Fig 4 5 b Explain using the voltage divider idea how this measures the input impedance When you re done with this exercise restore the 330 Q base resistor for use in the following parts gt Measure the output impedance To do so add a blocking capacitor and load resistor as shown in Fig 4 6 a and infer the output impedance from the small decrease in output amplitude see Fig 4 6 b The blocking capacitor allows the 330 Q load to affect the AC signal voltage without changing the DC biasing of the transistor a 15V b Emitter 330 Follower Vin 2N3904 ig ee a Vout 1 0 uF 3 3k Ou 330 Re 15V Fig 4 6 a Emitter follower with optional load circuit for measurement of Zout b Emitter follower modeled as an ideal voltage source in series with an output impedance 57 4 Bipolar transistors gt Explain what would happen to the DC bias voltage of the emitter if the capacitor were omitted When using the blocking capacitor be sure to use a small signal am
144. infinite resistance between the terminals marked When using an ohmmeter to check the resistance remember to measure it for both orientations of the terminals since you are dealing with diodes the resistance could be different in each direction gt Set up the bridge rectifier circuit of Fig 3 10 with Rg 10 k Insert the rectifier package straddling the central groove of a breadboard socket unit with the long dimension of the package running along the groove as shown in Fig 3 9 Four rectifier diodes can be used if a bridge rectifier is not available As before observe and record the voltage waveform across Ri gt Add a filter capacitor to the full wave rectifier as shown in Fig 3 11 a again be careful not to connect the capacitor backwards This form of power supply is very common Measure the average output voltage across the 10 k load Record the peak to peak ripple voltage gt Repeat these measurements for Ry 1 k Caution What power rating must the 1 k resistor have and why Use socket adapters to handle the fat leads of the 2 W resistor gt Repeat the ripple voltage calculations for these two values of Ri keeping in mind that the filter capacitor discharge time is now one half of the AC cycle To make this circuit into a complete power supply one would want to regulate the output that is employ feedback to make the output voltage and ripple less dependent on the load resistance This could be d
145. ing the cycle when neither transistor is on By how much does it reduce the output amplitude and why What is the minimum input amplitude required for an audible output Explain For high power applications a power Darlington push pull stage is often used Two methods can be used to alleviate the crossover distortion e shifting the bias points of the two transistors apart to minimize the portion of the cycle when neither transistor is on e using feedback to apply a signal to the bases that compensates for the distortion We will explore these techniques in Chapter 8 4 3 3 Common base amplifier Build the common base amplifier of Fig 4 12 gt Predict and measure the transistor s quiescent currents and bias voltages The diode at the base should bias the emitter approximately at ground Since the diode and base emitter voltage drops are unlikely to be exactly the same the input will have a small DC offset how big is it 64 Hands on electronics 15 Vout 2N3904 22 k 15 Fig 4 12 Common base amplifier gt Connect a small sine wave input and determine the voltage gain Note that in contrast to the common emitter amplifier the input and output currents are almost equal and the amplifier is noninverting gt What do you predict for the input and output impedances You can measure the input impedance easily using the 400 output impedance of the function generator how much smaller does the function ge
146. ing to the pinout diagram Fig 10 2 you will note that the ground connection is at pin 7 and 5 V at pin 14 a typical although not universal configuration Again disaster will strike if you hook up the chip backwards and apply power Carefully insert the 74HC00 so that it straddles the central groove of a breadboard section When inserting a new chip into the breadboard you need to pay attention to all of the pins and make sure none of them is bent since a bent pin will fail to make contact Check that the power is off Then run jumpers to pins 7 and 14 of the chip from the ground and 5 busses respectively For now we are going to use just one of the four gates on this chip the one whose output is at pin 3 and whose inputs are at pins 1 and 2 Connect pin 3 to an LED logic indicator Connect pins 1 and 2 to level switches Ground all other inputs After double checking that the connections are correct turn on the power Note the 74HC00 can source only 5 mA of current therefore if you use discrete components for your LED logic indicator you will need to buffer the output through a transistor This is most simply done using an N channel MOSFET connect the source to ground the gate to pin 3 of the 74HCO00 and the LED and current limiting resistor in series from the drain to the 5 V supply gt Connect the inputs to logic switches and try all four input combinations Record the truth table in terms of logic levels gt Connect p
147. integrated circuits with their greater ease of use before discrete devices or digital circuits with their simpler rules before the complexities of analog devices We have tried these approaches on occasion in our teaching and found them wanting Only by considering first the discrete devices from which integrated circuits are made can the student understand and appreciate the remarkable properties that make ICs so versatile and powerful A course based on this book thus builds to a pinnacle of intellectual challenge towards the middle with the three transistor chapters After the hard uphill slog it s smooth sailing from there hold onto your seatbelts The book includes step by step instructions and explanations for the following experiments 1 Multimeter breadboard and oscilloscope RC circuits Diodes and power supplies Transistors I Transistors II FETs Transistors III differential amplifier Introduction to operational amplifiers More op amp applications Comparators and oscillators Combinational logic OANA NMN PWN ji Flip flops saving a logic state xxi Introduction 12 Monostables counters multiplexers and RAM 13 Digital lt analog conversion These thirteen experiments fit comfortably within a sixteen week semester If you or your instructor prefers one or two experiments may easily be omitted to leave a couple of weeks at the semester s end for inde pendent stu
148. ion Eq 2 1 relates the voltage across a capacitor to the integral of the current Thus where the current through a capacitor leads the voltage across it the current through an inductor Jags the voltage across it by 90 With respect to its function in a circuit an inductor can thus be thought of as the opposite of a capacitor Whereas capacitors are relatively small light cheap and have negligible resistance inductors tend to be large heavy expensive and have appreciable resistance Nevertheless they find important use in filtering applications e g bandpass filters crossover circuits for hi fi speakers radio frequency circuits and so forth In the interests of time we omit inductor exercises from our course but if you understand capacitors you will have very little difficulty in applying inductors 2 1 2 Types and values of capacitors For some reason the various manufacturers conventions for marking ca pacitors are particularly confusing probably it has to do with the fact that many small value capacitors are physically too small to permit much print ing on them Some common sense is required Keep in mind that 1 farad is a huge unit Most capacitors are in the picofarad and microfarad ranges and these are the two commonly used units A physically large capacitor that says 10M on itis usually 10 microfarads not 10 millifarads for some reason most manufacturers don t want to print Greek letters so they
149. ip Another term for monostable multivibrator is one shot since it is a device that shoots once i e issues an output pulse each time it receives an input signal Among monostables the 555 timer is the best choice for pulse widths ranging from milliseconds to hours and for applications in which the pulse width must be stable to better than 0 05 In digital designs monostables such as the 74121 are preferred for pulse widths ranging from about 40 ns to 10 ms and will operate up to tens of seconds but their pulse widths are not as predictable or stable 12 2 Counters In the last lab you wired up a divide by four circuit That was of course a 2 bit binary counter Counters are so useful that IC manufacturers pro vide 4 bit and more counters as a single chip with carry in and carry out connections that allow them to be cascaded in multiple stages for 8 bit 12 bit or greater range Cascading means connecting multiple chips together as in the multiple digits of a car s odometer so that each chip 157 12 Monostables counters multiplexers and RAM counts when the preceding one rolls over from its maximum count back to zero Counters are available in both binary and decimal versions and in synchronous and asynchronous ripple through configurations with various arrangements of set reset and clock inputs Four bit binary counters count from 0 15 and then roll over to 0 again possibly issuing a carry
150. is slightly more complicated than the D flip flop it can do everything a D can do plus more The following exercises use a negative edge triggered JK flip flop with SET and RESET Various chips are available e g the 74HC112 or the 74LS76 which you use will depend on what you have to hand however for the following exercises we recommend using the 74112 JK flip flop Be sure to review the data sheet to ensure that you have the correct pinout 149 11 Flip flops Voc pin 16 Gnd pin 8 Fig 11 5 Pinout of the 74112 JK flip flop Tie SET and RESET high and explore the JK s clocked operation Note that the 74112 senses its J and K inputs only at downward transitions of the clock hence it is referred to as negative edge triggered gt Driving the clock from a debounced push button and J and K from logic switches check the four possible input states and write down the JK state table As in the case of the RS latch above you need to try each input state for both possible internal states gt Now add an inverter made from a NAND if you like from the J to the K input to make a D flip flop Drive J from a level switch and write down the state table to verify that the circuit acts like a D flip flop gt Next remove the inverter and connect J and K together Try it out and write down the state table What does this circuit do How is it different from the toggling D flip flop 11 4 Tri state outputs The ICs that we have
151. it directly charac terizes voltages but the other two nomenclatures rely on a convention 1 Also known as symbolic logic 127 10 Combinational logic ee Volts 5 EnF Vec Vec 4 EER Vin 3 Vec Vin 2 k Vin B Vi 1 Vit z Vit 0 CMOS CMOS amp TTL Low Voltage CMOS C HC AC and HCT ACT AHCT LVC and ALVC AHC Series S F LS AS and Series ALS Series Fig 10 1 Logic levels for various 7400 family lines Vcc is the most positive voltage Vi and Vy are the maximum input low and minimum input high voltages which can be assigned either of two ways The more common convention is positive logic high 1 true low 0 false But there are occasionally situations in which it is more convenient to employ negative logic in which high 0 false and low 1 true Another way to think about logic circuits isin terms of assertion level logic which is a hybrid of positive and negative logic that we will introduce in the next chapter 10 1 2 Logic families and history As indicated in Table 10 1 CMOS and TTL chips come in a plethora of types each with its own speed power dissipation input load and output current characteristics This reflects the historical development of the var ious series Since our initial purpose is to become familiar with the logic the details of speed and power are for now unimportant but you will need a general familiarity with them so as not to be in the dark when you encounter them in futur
152. it the high frequency gain to the ratio R R The output voltage as a function of time is still given by Eq 8 2 as long as the input frequency is small compared with 1 f IRC 8 4 For input frequencies greater than this the performance of the circuit approaches that of an inverting amplifier with voltage gain Re A Rs 8 5 8 1 2 Integrator By interchanging the resistor and capacitor in the differentiator circuit of Fig 8 2 we obtain an op amp integrator As shown in Fig 8 4 the resistor R is the input element and the capacitor C is the feedback element The output voltage as a function of time is given by Vout 1 Vint 8 6 C J 1 104 Hands on electronics op amp Vout Fig 8 4 Basic op amp integrator Vout Fig 8 5 Improved op amp integrator which is proportional to the time integral area under the curve of the input waveform vs time As in the case of the differentiator a more practical integrator circuit is shown in Fig 8 5 The resistor R across the feedback capacitor called a shunt resistor is used to limit the low frequency gain of the circuit If the low frequency gain were not limited the input DC offset although small would be integrated over the integration period possibly saturating the op amp To minimize the DC offset voltage resulting from the input bias current the resistor R should equal the parallel combination of the inp
153. ition 6 depends significantly on temperature collector current and collector to emitter voltage Since 6 can vary over a substantial range it is good practice to design transistor circuits in such a way that their proper functioning does not depend strongly on its exact value Because is so variable the current amplifier picture of transistor action is less useful than the transconductance amplifier picture 4 1 1 Basic definitions To discuss transistor action quantitatively we need to define three voltage differences three currents and the relationships among them e Veg Vg Vg potential of base relative to emitter e Vcg Vc Vg potential of collector relative to base 51 k 404 Region an I 40 4 Bipolar transistors e Vcr Vc Vg potential of collector relative to emitter e associated identity from Kirchhoff s voltage law Vcr Ver Vos 4 1 For an NPN transistor in its normal operating mode all the above potential differences are positive e Jc current flowing into collector e Ig current flowing out of emitter e Ig current flowing into base e associated identity from Kirchhoff s current law Ie c lg 4 2 For an NPN transistor in its normal operating mode all the above currents are positive The relationships between these voltages and currents are usually ex pressed in terms of characteristic curves Fig 4 3 displays sets of represen tative curves for an ar
154. k of the circuit you have just constructed and more If you have time look up this chip in a logic data book or on the web familiarize yourself with its operation and test it on your breadboard Describe how the function of this chip differs from the circuit you constructed in section 10 3 5 11 Flip flops saving a logic state Next we turn to flip flops Also known grandiosely as bistable multivibra tors these devices can remember their past Their behavior thus depends not only on their present input but also on their internal state Circuits containing flip flops are termed sequential logic circuits since their state depends on the sequence of inputs that is presented to them A truth table is not sufficient to describe the operation of a sequential circuit you need a timing diagram One category of sequential logic circuits is the finite state machine which goes through a predetermined sequence of states advancing to the next state each time it receives a clock pulse We will encounter some examples of state machines in this chapter including divide by two and divide by four counters A useful tool in understanding a state machine is a state diagram showing the sequence of states through which the circuit passes Some of these circuits will probably be the most complicated you have wired up so far Prepare carefully in advance and you will find you can complete these exercises easily if you are unprepared it is likely to t
155. keep the input amplitude less than about 700 mV You can check what happens to the output waveform as you exceed this amplitude but be sure not to exceed the 1 V reverse voltage capability of the input capacitor Also use a high enough frequency that the input high pass filter does not attenuate the signal too much it is a little tricky to estimate the breakpoint frequency of the filter because three resistances in parallel need to be taken into account those of the base bias voltage divider as well as the input impedance of the base gt Is the amplifier inverting gt Look at the signal at the emitter and explain what you see 59 4 Bipolar transistors SSS 5 15 2N3904 330 Fig 4 8 Transistor current source gt Try a triangle wave input can you see any distortion in the output waveform There should be some due to the variation of re with col lector current but the effect is small since re is in series with the 1 k emitter resistor How big should the effect be according to the Ebers Moll model In the grounded emitter amplifier i e for Rg 0 the voltage gain is greater but so is the distortion since re alone appears between the emitter and ground 4 2 4 Collector as current source Since the base collector junction is reverse biased the collector should act as a very high impedance This means that the collector is a good approximation to a current source a device that outputs a
156. le use them for the LE OE and D inputs in place of the resistor SPST switch combinations shown Be sure LE is high and OE is low Choose any one of the D Q pairs and apply a valid logic level to the D input Verify that the Q output follows the D input for both input states Measure the propagation delay between the input and output gt Set D high and observe the output voltage voltage at the output pin as you vary the potentiometer setting there is no need to be excessively quantitative here Repeat your observation with D low Explain why the potentiometer has little effect on the output voltage gt Set LE low Does the output logic level vary as the input changes Explain your observations Vcc 8Q 8D 7D 7Q 6Q 6D 5D 5Q LE Fig 11 6 a Pinout and power connections for the 74373 b Input and output connections for testing the tri state output Unlabeled resistors merely need to be large enough to prevent excessive current flow from 5 V to ground e g 1 k or larger 151 11 Flip flops gt Set LE high and OE high Observe the output voltage as you vary the potentiometer Explain your observations Does the output behave differently for input high and input low gt Now set the input either high or low record the input state then set LE low gt Set OE low The input state at the moment that LE was set low should have been latched internally independent of the state of OE Does the 373 remember the last input s
157. le if you are measuring a voltage with respect to ground But if you want to measure a voltage drop between two points in a circuit neither of which is at ground first observe one point with the probe and then the other The difference between the two measurements is the voltage across the element During this process the reference lead should remain firmly attached to ground and should not be moved Alternatively you can use two probes and configure the scope to subtract one input from the other Warning A short circuit will occur if the probe s reference lead is connected anywhere other than ground 1 3 2 Display Your oscilloscope user s manual will explain the information displayed on the scope s screen Record the various settings timebase calibration vertical scale factors etc gt Explain briefly the various pieces of information displayed around the edges of the screen The following exercises will give you practice in understanding the vari ous settings For each you should study the description in your oscilloscope user s manual The description below is specific to the TDS210 if you have a different model your manual will explain the corresponding settings for your scope 1 3 3 Vertical controls There is a set of vertical controls for each channel see Fig 1 4 These adjust the sensitivity volts per vertical division on the screen and offset the vertical position on the screen that corresponds
158. lectronics Rg that is in series with the emitter i e the apparent resistance seen at the base is B re Rg rge Reg which is typically tens to hundreds of kilohms We saw in the case of the silicon diode that a crude approximation in which the forward diode drop is taken to be approximately constant at 600 mV is adequate for most applications As mentioned above in many practical transistor applications including the circuits you will build in this chapter a simple approximation is sufficient treat the base emitter voltage difference Vgg as constant at about 700 mV and re as constant at a few ohms This reflects the fact that the order of magnitude for Ic in a typical small signal transistor circuit is several milliamperes Often re is much smaller than Rg and can be neglected 4 2 Experiments 4 2 1 Checking transistors with a meter Since a transistor is constructed as a pair of back to back PN junctions a quick way to test a transistor is to verify its junction resistances in the forward and reverse biased directions Often this can be done using an ohmmeter which sends current through the device under test and measures the resulting voltage However our digital multimeters are not designed for this kind of measurement instead they provide a diode test function that measures the forward voltage corresponding to a forward current of about 600 pA To test a diode or transistor junction connect it between the VQ and com
159. lm metal film or wound up wire en cased in an insulating coating with wire leads sticking out the ends Often the resistance is indicated by means of colored stripes according to the resistor color code Table 1 2 Resistors come in various sizes accord ing to their power rating The common sizes are i W 1 W 5 W 1 W and 2 W You can easily verify this linear relationship between voltage and current using the fixed 10 k amp 2 10000 ohm resistance provided between the two ends of one of the breadboard s potentiometers A potentiometer is a type of resistor that has an adjustable center tap or slider allowing electrical connections to be made not only at the two ends but also at an adjustable point along the resistive material The 10 k pot as it is called for short is located near the bottom edge of the breadboard and can be adjusted by means of a large black knob Inside the breadboard s case the ends of the pot as well as the center tap connect to sockets as labeled on the breadboard s front panel By pushing wires into the sockets you can make a series circuit Fig 1 3 consisting of an adjustable power supply the 10 k pot and the multimeter configured to measure current You can attach alligator clips to the meter leads to connect them to the wires But before doing so be sure to observe the following warnings e First turn off the breadboard power to avoid burning anything out if you hap
160. lso implies power amplification gate A circuit that performs digital logic such as an AND gate or a NOR gate ground Voltage reference point 0 V Also called common henry Unit of inductance hertz Unit of frequency 1 hertz 1Hz 1 cycle second impedance Degree to which a circuit element impedes the flow of current includes both resistive and reactive components In the standard electrical engineering notation resis tance is a real quantity and reactance is imaginary corresponding to their 90 phase difference thus impedance is given by Z R ix jack Connector used to accept a plug socket Kirchhoff s current law The net current flowing into or out of any point in a circuit is zero Kirchhoff s voltage law The total voltage around any closed loop is zero mho Unit of transconductance inverse of an ohm ohm Unit of resistance 1 ohm 1 Q 1 volt ampere plug Connector that plugs into a socket or jack quiescent Default voltage and or current values when an input signal is absent reactance Capacitive Xc and or inductive X component of a circuit element s impedance resistance Degree to which a device impedes the flow of DC current nonreactive component of impedance Measured in ohms For a nonreactive device also the degree to which the device impedes the flow of AC current i e for a resistor Z R slew rate Rate at which an output voltage changes socket Connector used to accept a plug jack Th v
161. ltage in a circuit negative supply voltage X reactance Z impedance Electrical devices ADC analog to digital converter C symbol used in schematics for a capacitor CMOS complementary MOSFET integrated circuit family CRT cathode ray tube DAC digital to analog converter ECL emitter coupled logic integrated circuit family FET field effect transistor JFET junction FET L symbol used in schematics for an inductor MOSFET metal oxide semiconductor FET op amp operational amplifier Q symbol used in schematics for a transistor can also refer to the latched output of a flip flop or register R symbol used in schematics for a resistor SPDT single pole double throw switch SPST single pole single throw switch TTL transistor transistor logic integrated circuit family 190 Pernt Hands on electronics T L Crossing lines are NOT connected unless marked Ground Voitage Source Function with a dot Lines forming a T are always connected Generator s Resistor Capacitor Polarized Diode Light Emitting Zener Capacitor Diode LED Diode c D B NPN N channel Transistor JFET S El G G E S P channel N channel E D MOSFET MOSFET B PNP P channel f D Transistor G JFET c S Transformer i Primary ete J lL Coil Push button Inverter Switch Normally Open 3 gt ee Samanta Push button XOR SPDT Normally Closed Secondary Coil NAND AND NOR OR Speaker Appendix C 191 RC circuits frequency domain analysis
162. ly burn out the pot rendering it useless If in doubt have someone check your circuit before turning on the power gt Use Ohm s law to predict the current that will flow around the circuit if you use the power supply that you set to its midpoint in the previous exercise What current should flow if the supply is set to its minimum voltage What is the current if the supply is set to its maximum voltage 8 Hands on electronics EEE gt Now turn on the breadboard power measure the currents for these three voltages and compare with your predictions Make a graph of voltage vs current from these measurements Is the relationship linear How close is the slope of voltage vs current to 10 KQ 1 2 3 Measuring resistance Now turn off the breadboard power and disconnect your series circuit In this and the following part the pot should connect only to the meter gt Set the meter for resistance and measure and record the resistance between the two ends of your 10 k pot Due to manufacturing tolerances you will probably find that it is not exactly 10 k2 By what percentage does it differ from the nominal 10 kQ2 value Does the measured value agree more closely with the slope you previously measured than with the nominal value Explain gt Now connect the meter between the center tap and one end of the pot What resistance do you observe What happens to the resistance as you turn the potentiometer s knob gt Leaving the knob in o
163. ly voltage Now connect a 555 as shown in Fig 9 6 b The output should be a one shot pulse of duration t 1 1RAC 9 4 The output pulse is triggered by the push button switch which causes the TRIGGER input to go to ground Note the output will remain high indef initely if the TRIGGER input is held at ground so one should ensure that the trigger pulse is shorter than the desired output pulse Time the output pulse by observing the LED gt Briefly explain the operation of this circuit What prevents this circuit from oscillating gt Measure the output pulse duration for several values of Ra and C Tab ulate your results gt Derive Eq 9 4 Are your data consistent with this expression If not why not 121 9 Comparators and oscillators SSS 9 2 Additional experiments 9 2 1 Alarm You can configure the 555 to sound an alarm when prompted by an external signal The alarm is simply a 555 oscillator with the output connected to a speaker To prevent the alarm from sounding continuously ground is ap plied to the RESET input pin which overrides the TRIGGER and THRESHOLD pins and forces the output near ground When used in this way the RESET line is said to enable the 555 enabling oscillation when high while dis abling oscillation when low Build the circuit as shown in Fig 9 7 Use a long wire which simulates a security loop Cut or unplug the wire and hear the alarm The alarm can also be configur
164. mon jacks with clip leads and set the meter s selector knob to the position marked with the diode symbol The diode is forward biased if its anode is connected to VQ and its cathode to common gt Test the base collector and base emitter junctions of a 2N3904 NPN and 2N3906 PNP and record your readings in both the forward and reverse biased directions To tell which pin of the transistor is which refer to Fig 4 4 which shows the pinout for the TO 92 plastic case in which these transistors are packaged If your transistors are good each junction should show about 700 mV in the forward direction and an out of range indication in the reverse direction 55 4 Bipolar transistors a b E C E C id io E A pi F B B case NPN PNP E B E 3 Fig 4 4 Transistor as back to back diodes TO 92 pinout a 15V b Emitter i Follower 2N3904 Vout 15V Fig 4 5 a Emitter follower b Emitter follower model used for input impedance measurements The value for Zin is found using the voltage divider equation 4 2 2 Emitter follower This simple transistor circuit shown in Fig 4 5 a is often used to buffer an AC signal as well as to change its DC voltage level by Vgg It is also a close relative of the common emitter amplifier that we will study next It is called an emitter follower because the voltage at the emitter follows voltage changes at the base with Vgg almost constant at
165. mplete Rectifier Circuit Fig 3 12 A rectifier circuit can be modeled as a Th venin equivalent using an ideal voltage source in series with an output impedance The output impedance is measured by observing the output voltage as a function of the output current Zou A Vout A Lout and your data on V y vs RL compute the circuit s output impedance Zout in ohms gt As another example determine the output impedance of your bread board s function generator by measuring its sine wave output amplitude first with no load and then with a load resistance of 1 k to ground If the output impedance has negligible frequency dependence it can be approximated as a pure resistance in which case the function generator s Th venin equivalent circuit consists of an ideal AC voltage source one having zero internal resistance in series with a single resistor gt Check the function generator s Zout both at low and high frequencies say 50 Hz and 50 kHz do you observe any appreciable frequency dependence gt Sketch schematic diagrams with component values labeled of the Th venin equivalent circuits of your voltmeter full wave rectified power supply and function generator 4 Bipolar transistors Invented in 1947 transistors and integrated circuits made from them have been the basis for the explosive proliferation of electronic devices that revolutionized so much of life in the latter half of the twentieth cent
166. mplifier 6 Transistors Ill differential amplifier 6 1 Differential amplifier 6 1 1 Operating principle 6 1 2 Expected differential gain 6 1 3 Measuring the differential gain 6 1 4 Input offset voltage 6 1 5 Common mode gain 6 2 Op amps and their building blocks 6 2 1 Current mirror 6 2 2 Differential amplifier with current source loads 6 2 3 Improved current mirror 6 2 4 Wilson current mirror 7 Introduction to operational amplifiers 7 1 The 741 operational amplifier 7 1 1 741 pinout and power connections 7 1 2 An ideal op amp 7 1 3 Gain of inverting and noninverting amplifiers 7 1 4 Op amp golden rules 7 1 5 The nonideal op amp 62 63 65 65 66 68 69 69 70 71 73 75 75 76 76 77 78 78 79 79 80 82 82 85 85 86 87 88 90 90 viii Contents Le 7 2 Experiments 7 2 1 Testing open loop gain 7 2 2 Inverting amplifier 7 2 3 Noninverting amplifier 7 2 4 Voltage follower 7 2 5 Difference amplifier 7 3 Additional experiments 7 3 1 Current source 7 3 2 Noninverting summing amp with difference amplifier 8 More op amp applications 8 1 Op amp signal processing 8 1 1 Differentiator 8 1 2 Integrator 8 1 3 Logarithmic and exponential amplifiers 8 2 Experiments 8 2 1 Differential and integral amplifiers 8 2 2 Logarithmic and exponential amplifiers 8 2 3 Op amp active rectifier 8 2 4 Op amp with push pull power driver 8 3 Additional exercises 9 Comparators and oscillators 9 1 Exper
167. n different input signals It can also be used to implement logic functions For example by connecting each of the n inputs to low or high in a desired pattern any desired 1 bit logic function of the input number can be produced You can also use a mux plus a counter to generate an arbitrary timing pulse sequence on each clock cycle a different input will be selected and the output will be either high or low depending on the state of the corre sponding input This is an example of a finite state machine it repeatedly goes through a cycle of n internal states Finite state machines are often useful in control applications e g in deciding when to open the hot water valve in a washing machine Hook up the select inputs A D of a 150 16 to 1 multiplexer Fig 12 6 to the outputs of the low order counter chip from the previous exercise leave them connected to the hex display also Note that the 150 has an ENABLE input that needs to be held low Since the 150 is an inverting mux if you want its output to be high during counter state i ground data input i gt Which select input is high order and which is low order What experi ment can you do to find out Do it and find out gt As an example of an arbitrary logic function configure the 150 to identify which of the numbers from 0 9 are prime Hard wire the inputs appropriately and connect the 150 output to a logic indicator Clock the counter from a debounced push button
168. n emitter amplifier 58 Hands on electronics 2 Then apply Ohm s law to the emitter resistor to determine the emitter current taking into account the transistor s expected Vgg drop Ig Vg Vpe Re 3 Then apply Ohm s law to the collector resistor to determine the quiescent collector voltage Vou Voc Jc Rc You know the collector current well enough since it equals the emitter current to a good approximation gt Compared to your measurements by what percentages are your voltage predictions wrong Is this as expected given the resistor tolerances and uncertainties in 6 and Vgg gt Using the measured voltages predict the collector emitter and base currents gt Calculate the change in quiescent base voltage if you take the base current into account Assume that the base current flows through the Th venin equivalent of the base bias voltage divider i e the input impedance of the base is in parallel with R2 You can understand how the circuit amplifies by applying Ohm s law to the emitter and collector resistors Since the emitter follows the base a voltage change at the base causes a larger voltage change at the collector AVour Alc Rc Alg Re Alg AVg Re AVg RE AVin RE 4 10 Therefore AVout AVinRc Re 4 11 gt Measure the voltage gain AVou AVin and compare with what you expect So as not to exceed the available output voltage range of the circuit be careful to
169. nalog IC s four Si signal diodes one 1 A Si rectifier diode two 3 3 V 1 W Zener diodes one 5 1 V 1 W Zener diode one diode bridge element one red light emitting diode three 2N3904 NPN transistors three 2N3906 PNP transistors two VP0610L MOSFETs two VN0610N MOSFETs two 2N5485 N channel JFETs one 411 op amp one 555 timer three 741 op amps one 311 comparator Miscellaneous four alligator clips two fat pin adapter sockets Digital components Component Number required 7400 7404 7432 7474 7485 7486 7489 7490 7493 74112 74121 74138 74150 74191 74373 DAC0806 ADC0804 TIL311 N o e e e e e e e a e N l ee See 187 Appendix A Equipment and supplies Suppliers of parts There are numerous companies selling electronic components and supplies Most allow customers to purchase small quantities directly over the web Prices are reasonable and service is excellent Several e g Digi Key Corp even have links to product data sheets as part of their online catalog Product information availability and pricing are easily found through a few quick web searches We ve included a few URLs to help get you started At the time of going to press the parts and supplies needed to complete the exercises within this book could be purchased from the companies below Pricing and availability may vary so shop around RadioShack http www radioshack com Digi Key Corp http www digikey com Newark
170. nce on them Since the transconductance of a bipolar transistor increases linearly with Ic 8m bipolar 1 re but that of an FET only as the square root of Ip bipolar transistors typically have higher transconductance than FETs for a given current and thus can give higher gain in amplification appli cations This has led to the common practice of combining FETs with bipolar transistors in analog integrated circuits to exploit the advantages of both e g the CA3140 MOSFET input op amp with its teraohm input impedance 69 5 Transistors Il FETs SS 5 2 Exercises 5 2 1 FET characteristics As shown in Fig 5 1 the gate source and gate drain connections are PN junctions gt Use the diode test feature of the multimeter and verify this picture us ing a 2N5485 JFET the pinout for the 2N5485 is shown in Fig 5 4 Note the pinout of the 2N5485 does not correspond to that of the 2N3904 Unlike an NPN transistor whose emitter and collector are distinct N type regions separated by the P type base the drain and source of an N channel JFET occupy opposite ends of a single N type region connected via the channel gt Use an ohmmeter to show that the drain and source are connected If the meter reading fluctuates try connecting the gate and source together using the breadboard and a small piece of wire Explain why this will stabilize your measurement What resistance do you measure Next verify Eq 5 1 To measure pss and Vp set
171. nces of states How is the contact bounce affecting the sequence RS latch as debouncer Now use the RS latch from the first exercise as a switch debouncer Fig 11 9 b Although D and JK flip flops are used for most flip flop applications switch debouncing is one area in which RS latches continue to hold their own gt Connect the switch to the latch as shown and use the output from the latch to clock the counter Verify that the counting sequence is now correct Explain why this works The PB 503 s momentary contact switches are already debounced by RS latches built into the unit 11 5 3 Electronic coin toss The RS latch debouncer from the previous section can be combined with a D type flip flop to create an electronic coin toss game To build the circuit connect the output of the RS latch debouncer to the clock input of a D type flip flop Connect the digital output of the function generator to the D input and connect the Q output to a logic indicator Set the function generator 154 Hands on electronics frequency to about 10 Hz Operate the switch and observe the output You can assign the LED on to be heads and off to be tails gt Write down the circuit diagram with pin numbers and explain how this circuit works gt Record a sequence of ten coin tosses Is the sequence random Repeat another sequence of ten How many tosses are required to determine if the system is truly random If you were an unscru
172. nd corner of Fig 13 7 Pay particular attention to the sequence and timing of signals at the beginning and end of the conversion cycle and see if you can figure out the answers to the following questions In what state does the counter start out In what state does it end Exactly what function does each decoder enable perform Hint each performs a slightly different function What happens if you attempt to start anew conversion cycle while one is already in progress Why is it important for the control flip flops to be negative edge 179 13 Digital lt gt analog conversion Q3 Q2 Q1 Qo D 74191 U D Fig 13 6 Control logic for 8 bit successive approximation ADC triggered can the clock signal to the 191 glitch i e have a pulse of sub standard width see discussion in section 12 3 2 Why or why not Begin by building and debugging the control logic by itself but be sure to leave room for the additional chips If you prefer you may choose to build and analyze the simpler control logic described below Try to arrange the chips and connecting wires neatly so that it is easy to see where each wire goes some color coding could be helpful In case a chip needs to be replaced try to avoid overly tight wiring across the top of any chip Clock your control circuit with a digital square wave from the function generator and provide the START CONVERT signal with a debounced push button You should be able to see
173. nd has the value o 8 854 x 107 F m The farad is an impractically large unit for a conductor area of 1 cm and separation of 1 mm with dielectric constant of order 1 the capaci tance is picofarads To achieve the substantially larger capacitances of order microfarads often found in electronic circuits manufacturers wind ribbon shaped capacitors up into small cylinders and use insulators of high dielectric strength such as ceramics or in the so called electrolytic ca pacitors special dielectric pastes that chemically form an extremely thin insulating layer when a voltage is applied Table 2 1 gives dielectric con stants for some typical dielectrics used in capacitors Capacitors thus come in a variety of types categorized according to the type of dielectric used which determines how much capacitance can be squeezed into a small volume Electrolytic and tantalum capacitors are polarized which means that they have a positive end and a negative end and the applied voltage should be more positive at the positive end than at the negative end if you reverse voltage a polarized capacitor it can burn out or even explode Paper mica and ceramic capacitors are unpolarized and can be hooked up in either direction The large dielectric constants of the polarized dielectrics permit high capacitance values up to millifarads in a several cubic centimeter can 17 2 RC circuits a 2 1 1 Use of capacitors review of AC circuits T
174. ne place measure and record the resistance between the center tap and each end Do the two measurements add up to the total you measured above They should explain why 1 3 Oscilloscope With its many switches and knobs a modern oscilloscope can easily in timidate the faint of heart yet the scope is an essential tool for electronics troubleshooting and you must become familiar with it Accordingly the rest of this laboratory session will be devoted to becoming acquainted with such an instrument and seeing some of the things it can do The oscilloscope we use is the Tektronix TDS210 illustrated in Fig 1 4 If you don t have a TDS210 any dual trace oscilloscope analog or digital can be used for these labs as long as the bandwidth is high enough ideally 30 MHz or higher While the description below may not correspond exactly to your scope with careful study of its manual you should be able to figure out how to use your scope to carry out these exercises The TDS210 is not entirely as it appears In the past you may have used an oscilloscope that displayed voltage as a function of time on a Volts per Division 1 Equipment familiarization HORIZONTAL AUTOSET Seconds per MEASURE CONTROLS Division CURSOR TDS 210 ge TRIGGER LEVEL TRIGGER MENU CALIBRATION MENG SEC DIV VOLTS DIV CONTACT POINT OPTION babes BUTTONS CONTROLS Fig 1 4 Illustration of the Tektronix TDS210 digital oscilloscope The basic fe
175. ne wave input in the neighborhood of 100 Hz Record the input and output waveforms This circuit suffers from a drawback there is effectively no feedback during the half of the input wave cycle when the diode is reverse biased This is obvious since the voltages at the inverting and noninverting inputs are not equal during that time In other words the reverse biased diode has such a large impedance that the gain becomes very large and the op amp saturates gt To verify this look at the waveform at the op amp s output pin Because of the limited slew rate of the op amp saturation limits the circuit s performance at high input frequencies Try a high frequency say 10 kHz and record in detail what you see both at the op amp output and at the rectifier output Replace the 741 with a higher speed op amp such as the LF411 and repeat your observations Also be sure to use a signal 8 More op amp applications V out Fig 8 8 a Simple op amp half wave rectifier b improved version or switching diode like the 1N914 while switching diodes are designed for high frequencies rectifier diodes e g the 1N4001 tend to have large junction capacitance and thus have poor performance at high frequency The circuit of Fig 8 8 b overcomes the slew rate limitation gt Build it try it out and figure out why it has much better response at high frequency Explain how each circuit works use diagrams if necessary and explain w
176. need By varying the clock speed you can trade off fidelity sampling rate for message length e g at 1 kHz sampling rate you would be able to store 32 s worth of sound Try recording a sound sample then playing it back at various speeds You can also try adding nonlinear gain elements say a logarithmic amplifier or filtering to see how the sound is affected Can you figure out a way to program reverb For faithful recording it is important that the input voltage be constant during the entire time of the conversion This can be accomplished using a sample and hold amplifier SHA to sample the input and hold it until the conversion is complete The National Semiconductor LF398 is an SHA IC Pin 1 is connected to 15 V and pin 4 is connected to 15 V There are separate analog and logic inputs on pins 3 and 8 respectively and the output is at pin 5 Ground pin 7 An external capacitor 1000 pF is connected between pin 6 and ground This capacitor is used to hold the analog data until the ADC has had an opportunity to process it 178 Hands on electronics PE If you choose to add a sample and hold what additional control logic is needed Can you hear the difference it makes in fidelity How would you describe the difference and how would you explain it 13 4 2 Successive approximation ADC built from components To see first hand how the successive approximation algorithm works you can build an 8 bit ADC using TTL or CMOS parts plu
177. nerator output become when you connect it to the amplifier input What input impedance does this imply for the amplifier Explain 5 Transistors Il FETs In this chapter we introduce the field effect transistor FET A majority of today s integrated circuits are built using FETs of one type or another FET operation is easier to explain than that of bipolar transistors however due to the variability of FET parameters many people find FETs more difficult to use As with bipolar technologies it is essential that you master the basics of FET operation and you will find that knowledge useful later on Apparatus required Breadboard oscilloscope multimeter two 2N5485 JFETs one 1N4733 Zener diode two 1 k one 3 3 k two 10 k one 100 k and one 1 M 1 W re sistors 0 1 pF ceramic capacitor 1 0 wF and 100 uF electrolytic capacitors 5 1 Field effect transistors 65 Like bipolar junction transistors field effect transistors FETs are three terminal semiconductor devices capable of power gain Qualitatively they operate much like junction transistors but they have much higher input impedance and lower transconductance and voltage gain Also they have a larger variation in their Vgg equivalent called Vgs than bipolar tran sistors They come in a confusing variety of types but we will concentrate for today on junction FETs JFETs Fundamentally there are two types of FETs junction FETs and metal oxide semiconducto
178. never the input signal crosses that volt age so that many images of the signal occurring one after another can be superimposed in the same place on the screen The LEVEL knob sets the threshold voltage for triggering You can select whether triggering occurs when the threshold voltage is crossed from below rising edge triggering or from above falling edge triggering using the trigger menu or for some scope models using trigger control knobs and switches You can also select the signal source for the triggering circuitry to be channel 1 channel 2 an external trigger signal or the 120 V AC power line and control various other triggering features as well Since setting up the trigger can be tricky the TDS210 provides an automatic setup feature via the AUTOSET button which can lock in on 13 1 Equipment familiarization almost any repetitive signal presented at the input and adjust the voltage sensitivity and offset the time sensitivity and the triggering to produce a stable display gt After getting a stable display of the calibrator signal adjust the LEVEL knob in each direction until the scope just barely stops triggering What is the range of trigger level that gives stable triggering on the calibra tor signal How does it compare with the amplitude of the calibrator waveform Does this make sense Explain Next connect the scope probe to the breadboard s function generator you can do this by inserting
179. nobs CHHHHHHHHHHHHHHHAHHHHHAHHHHAHHHHHAHHHHAHHHHHHHHHHHHHH4 O HHHH O i 0 0 0 0 0 Horizontal Row ooo a Group of 5 0000 0 0000 0 0000 0 00000 0 0 0 0 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Amplitude 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Slider 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Frequency 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Slider 00 0 0 0 00 000 0 0 0 0 0 0 0 0 0 0 00 0 0 0 00000 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Function 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 Generator 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
180. nput frequency exceeds the sampling frequency Make several sketches of the input and output waveforms at various frequencies and comment on your observations Explain the re lationship between sampling frequency and output frequency response 177 13 Digital lt gt analog conversion gt Experiment with triangle and square waves of various frequencies Record and sketch a few input and output waveforms and comment on your results Be careful not to exceed the allowed input range As discussed above A D and D A conversions are merely approxima tions Higher precision and higher sampling rates improve the approxi mation at the expense of increased cost and data size For example let s say we re recording the sound track for a TV commercial To digitize and record a 30 s waveform with 8 bit precision and 10 kHz sampling rate requires 2 4 Mbit of memory storage Increasing the precision to 16 bit and sampling rate to 100 kHz increases the required space by a factor of 20 to 48 Mbit 13 4 Additional exercises 13 4 1 Digital recording You can convert your A D D A circuit into a digital recording and audio processing system by adding an audio input a memory to store the digital data and an audio output You can use speakers for both input and output buffered with suitable op amp circuits The 32 k x 8 CY62256 memory chips require a 15 bit address counter which you can make from 7493s or 74191s What other control circuitry do you
181. nts gt What is Vos for each data point 71 5 Transistors Il FETs open 15 10k pot Q 2N5485 Fig 5 5 Self biasing JFET current source You can compute Vgs from p and the known resistance of Rs You should see the drain current start to vary substantially as you make the transition from the saturation region to the linear region gt What is the compliance gt Within the saturation region how constant is the current gt Calculate the approximate output impedance in the saturation region see Eq 3 13 gt Compare the performance of this current source with that of the bare JFET and of the bipolar current source that you built in section 4 2 4 Even though Vas is not exactly constant as Vps is varied this circuit actually works better has larger output impedance than one in which Vgs is held constant This is because negative feedback is at work For example suppose Ip increases then so does the drop across Rs increasing the mag nitude of Vgs and moving the FET closer to pinch off thus decreasing Jp 5 2 3 Source follower As with the emitter follower from section 4 2 2 a JFET source follower provides power amplification via current buffering even though the voltage gain is less than or equal to unity Build the circuit of Fig 5 6 and try it out with a 1 kHz sine wave of small amplitude The operation of this circuit is reasonably straightforward Given the nanoampere gate current the 1 M re
182. o that the output sits near zero volts gt Vary the input in steps of 100 or 200 V over a range that causes the out put to vary from its maximum negative voltage to its maximum positive voltage taking several readings of input and output voltage as you do so You may find that the output switches states within a single step Approximately what input voltage would result in an output voltage near zero This is the input offset voltage of your 741 gt What are the op amp s positive and negative output saturation voltages i e the maximum voltages it can output If your chip has particularly high gain you may find that no setting of the input voltage causes the output to sit near zero volts however you can still set upper and lower limits on the input offset voltage by determin ing at what input voltages the output switches between its negative and positive saturation voltages Since your applied input voltages are so tiny the output voltage is very susceptible to input noise and you may also observe substantial drift of the output voltage with time Still you should 15 10k 15 op amp Vout Fig 7 4 Open loop op amp test circuit 92 Hands on electronics be able to estimate the gain roughly or at least place a lower limit on it gt What gain do you observe Is it consistent with the manufacturer s spec ification gain typical 200 000 You may find that stability and noise are improved by keepin
183. oards we use represent a great step forward in convenience since they include not only sockets for plugging in components and connecting them together but also power supplies a function generator switches logic displays etc The exercises that follow were designed using the Global Specialties PB 503 Protoboard If you do not have access to a PB 503 any suitable breadboard will do provided you have a function generator and two variable power supplies Additional components that you will need along the way that are built into the PB 503 include a 1 k and a 10 k potentiometer a small 8 Q speaker two debounced push button switches several LED logic indicators and several on off switches Fig 1 1 displays many of the basic features of the PB 503 For simplic ity some PB 503 features that will be used in experiments in later chapters have been omitted While the following description is specific to the PB 503 many other breadboards share some if not all of these features The description will thus be of some use for users of other breadboard models as well The breadboard s sockets contain spring contacts if a bare wire is pushed into a socket the contacts press against it making an electrical connec tion The PB 503 s sockets are designed for a maximum wire thickness of 22 AWG American Wire Gauge anything thicker i e with smaller 3 1 Equipment familiarization es Gs so O 15V Voltage Adjustment K
184. oduct of the two 6 s and whose Vgg drop is the sum of the two Vgg s Build the circuit of Fig 4 10 gt With the input grounded what quiescent currents do you observe through Rg and Rg What does this imply for the combined 6 value of the Darlington pair gt Now apply an input signal what do you see at the output What is the DC voltage drop from input to output 62 Hands on electronics 15 Q Q 2N3904 Vout Fig 4 10 Darlington pair gt The input impedance should be so big that you can t measure any de crease in signal amplitude across the 10 k resistor check this assumption What minimum value does this imply for the input impedance What input impedance do you expect and why Darlington pairs are available encapsulated in three lead packages for example the 2N6426 with combined value of about 100 000 The Darling ton connection is particularly useful for power transistors to compensate for their low 6 8 20 is not uncommon For example the TIP110 50 W power Darlington has a minimum combined value of 500 4 3 2 Push pull driver To provide low output impedance a push pull buffer stage is often used This consists of two emitter followers one PNP and one NPN arranged so that the PNP conducts during one half of the output period when Vout lt 0 and the NPN during during the other half Vou gt 0 gt First drive your breadboard s speaker nominal impedance 8 2 fr
185. of substandard width might be produced see Fig 12 5 Similarly since the one shot pulse might end during a clock pulse a substandard pulse might also be produced then Since substandard clock pulses might fail to meet setup or hold requirements of flip flops and counters it is wise to avoid gating clocks whenever possible When gating a clock is necessary one normally uses a pulse synchronization circuit such as the 74120 or a pair of cascaded flip flops to ensure that signals used to gate clocks do not change state during the clock pulse gt Why is your circuit insensitive to this problem substandard clock pulses Gated Clock Gate Clock Fig 12 5 Substandard outputs can result when gating clock signals 162 Hands on electronics The 74123 ICs have several additional features that we haven t explored here For example the 123 is a retriggerable monostable equipped with a CLEAR input The retrigger feature allows the output to persist longer than the time specified by Eq 12 1 through the application of additional TRIGGER edges while the output pulse is in progress CLEAR allows the output to be prematurely terminated See the data sheets for details and operating rules 12 3 3 Multiplexer and finite state machine A multiplexer or mux is a device that connects one of n inputs to a single output under control of an input number in the range 0 to n 1 It can thus be used to select among
186. om the function generator With the amplitude set to maximum and the frequency at 1 kHz measure the function generator amplitude both with and without the speaker connected What is the attenuation due to the 8 Q load Is it consistent with the measurement of the function generator s output impedance you made in section 3 7 Since the speaker impedance may depend on frequency repeat the mea surement at 10 kHz and compare Go back to 1 kHz and add a push pull buffer as shown in Fig 4 11 Be sure you have adjusted the supply voltages to not more than 5 V so as not to overheat the transistors they are rated for 200 mA collector current and 625 mW power dissipation You should see a larger output amplitude and hear a louder tone from the speaker 63 4 Bipolar transistors 5 2N3904 2N3906 Speaker 5 Fig 4 11 Driving loudspeaker with push pull buffer The circuit may oscillate because of inadvertent positive feedback from output to input if it does try 1 rearranging your circuit so that the wire jumpers are as short as possible 2 adding a 330 Q resistor in series with the input and if that s not enough to stabilize it 3 adding a few hundred picofarad cap to ground at the output gt The output waveform will display crossover distortion what does it look like and why does it occur Hint for a transistor to be on there must be about 700 mV between base and emitter is there a time dur
187. on applies also to PNP transistors but with the current carriers and directions reversed In normal transistor operation the base emitter diode is forward biased and the base collector diode is reverse biased Fig 4 2 The depletion region between the base and the collector extends essentially throughout the thin base region creating an electric field as shown in Fig 4 2 and blocks the flow of majority current carriers holes flowing from base to collector and electrons flowing through the collector to the base At the same time the emitter lead injects electrons into the emitter which flow across the forward biased base emitter junction While as just stated the base collector bias inhibits the flow of holes from the base into the collector the electrons with which the base is now filled are drawn by the electric field through the junction and into the collector They do this even though the base collector junction is reverse biased This is the essence of transistor action Essentially the construction of the transistor results in large numbers of the wrong current carrier entering the base and then continuing downhill into the collector Typically 99 of electrons entering the base from the emitter continue into the collector and only 1 emerge as base current The base current results from the small fraction of electrons entering the base that combine 50 Hands on electronics Table 4 1 A diverse selection
188. one using Zener diodes but a more effective technique is a transistorized regulating 45 3 Diodes Transformer Bridge Rectifier fuse 120 a Vac b ale sS lt 12 Fig 3 11 a Full wave rectification with filter capacitor b waveform produced by circuit shown in a circuit Integrated three terminal voltage regulators such as the 7800 and 7900 series have made this particularly simple i 3 7 Input and output impedance Input and output impedance are key ideas that are used all the time in analyzing circuits You ve already encountered the input impedance of the scope or voltmeter in section 3 5 A good way to think about the effect of an instrument on the circuit to which it is connected is via the instrument s Th venin equivalent The Th venin equivalent of the multimeter when set to measure voltage is a large resistor in parallel with an ideal voltmeter Fig 3 5 In practice an input also has some small capacitance and inductance and hence is more completely characterized by its impedance vs frequency which takes into account both the resistance and the capacitive and inductive reactances Outputs can also be characterized by their impedance see Fig 3 12 You ve already taken data that determine the output impedance of your filtered full wave rectifier circuit gt From Zout AVout A Tout 3 13 46 Hands on electronics Output Impedance Ideal Voltage Source out i et a Co
189. op amp one of the most useful devices for analog signal processing Probably the most surprising thing about op amps is their very large voltage gain usually exceeding 100 000 This chapter will give you a clearer idea how such performance is achieved We will also look at some other circuits that serve as building blocks for op amps Apparatus required Breadboard oscilloscope multimeter three 2N3904 and three 2N3906 transistors one 5 1 V Zener diode three 100 Q five 10 k two 22 k one each of 560 Q 2 2 k and 100 k 1 W resistors 6 1 Differential amplifier A differential amplifier is an amplifier for differential input signals i e it amplifies the voltage difference of its two inputs This is useful in two important ways 1 A differential amplifier can be used to amplify a differential signal the voltage difference between the two inputs while suppressing any noise that is common to the two inputs 2 As we will see in future chapters differential amplifiers make it easy to build circuits that use negative feedback Don t confuse the differential amplifier with the differentiator although the names sound similar the two circuits perform entirely different operations gt What does each do 75 76 Hands on electronics b Vout 10k Vin Vin Function 100 generator Fig 6 1 a Differential amplifier b function generator with 100 to 1 attenuator 6 1 1 Operating principle Fig 6 1 a shows
190. or external adjustment of the offset The input offset voltage must be considered when designing small signal or high gain cir cuits For the 741C op amp the input offset voltage is specified to be less than 6 mV Input bias current Slew rate An ideal op amp would draw no current at its inputs however real op amps require a small input bias current for proper operation You can think of this as the equivalent of the base current for a bipolar transistor or the gate current of a JFET Although these currents are small they are not zero For the 741C op amp the input bias current is specified to be less than 500 nA The output voltage of a real op amp cannot change instantaneously The maximum rate at which the output can change is called the slew rate and is typically in the range of volts per microsecond The slew rate can be a serious limitation at large output amplitudes and high frequencies The 741 slew rate is typically 0 5 V s High speed op amps are available with slew rates of 2000 V s 91 7 Introduction to op amps aS 7 2 Experiments 7 2 1 Testing open loop gain First try a 741 in the open loop circuit shown in Fig 7 4 As mentioned above open loop means that there is no feedback connection between the output and input op amps are never actually used in this way The 1000 to 1 attenuator in the input circuit means that by adjusting the pot you can vary the input between 15 and 15 mV Try to adjust the input s
191. ormation on this title www cambridge org 9780521815369 Cambridge University Press 2003 This book is in copyright Subject to statutory exception and to the provision of relevant collective licensing agreements no reproduction of any part may take place without the written permission of Cambridge University Press First published in print format 2003 ISBN I3 978 0 511 07668 8 eBook EBL ISBN IO 0 5II 07668 1 eBook EBL ISBN I13 978 0 521 81536 9 hardback ISBN I1O 0 521 81536 3 hardback ISBN I3 978 0 521 89351 0 paperback ISBN IO 0 521 89351 8 paperback Cambridge University Press has no responsibility for the persistence or accuracy of URLS for external or third party internet websites referred to in this book and does not guarantee that any content on such websites is or will remain accurate or appropriate Contents List of figures page xi List of tables XV About the authors Xvi To the Reader xvii Acknowledgments xviii Introduction X1X a 1 Equipment familiarization multimeter breadboard and oscilloscope 1 1 1 Multimeter 1 1 2 Breadboard 2 1 2 1 Measuring voltage 4 1 2 2 Measuring current resistance and Ohm s law 2 1 2 3 Measuring resistance 8 1 3 Oscilloscope 8 1 3 1 Probes and probe test 10 1 3 2 Display 11 1 3 3 Vertical controls 11 1 3 4 Horizontal sweep 12 1 3 5 Triggering 12 1 3 6 Additional features 13 Eas 2 RC circuits 15 2 1 Review of capacitors 15 2 1 1 Use of capacitors review of AC circ
192. ou derive the amplitude from something the scope does measure gt Using the measurement features determine the amplitude frequency and period of a waveform of your choice from the function generator 14 Hands on electronics You can also use the on screen cursors to make measurements gt Use the cursors to measure the half period of the signal you just measured gt Explain how you made these measurements and what your results were A feature that comes in particularly useful on occasion is signal averaging this is programmed via the ACQUIRE button and allows noise which tends to be random in time to be suppressed relative to signal which is usually periodic i RC circuits Capacitors are not useful in DC circuits since they contain insulating gaps which are open circuits for DC However for voltages that change with time a simple series circuit with a capacitor and a resistor can output the time derivative or integral of an input signal or can filter out low frequency or high frequency components of a signal But before plunging into the world of time varying voltage and current i e alternating current circuits we explore the voltage divider idea using direct current since it gives us a simple way to understand circuits containing more than one component in series Then we apply it to the analysis of RC circuits as filters Note that the series RC circuit can be analyzed in two different ways e via the exponent
193. ower loading Three schematics representing a resistive voltage divider The voltage divider concept for RC circuits High pass filter or voltage differentiator Relationships among input voltages and capacitor and resistor voltages for high and low pass RC filters Representation of a junction between P type and N type semiconductor material Diode circuit symbol and biasing Typical current voltage characteristics for germanium and silicon diodes Representation of physical diodes and symbols used in circuit diagrams Measuring the forward characteristic of a diode Power transformer supplies Vou 25 V r m s Power transformer with half wave rectification Half wave rectifier with filter capacitor An example of how to insert a diode bridge into a breadboard Full wave rectification using diode bridge Full wave rectification with filter capacitor Complete rectifier circuit Construction and circuit symbols and biasing examples for NPN and PNP junction transistors page 3 18 21 22 24 27 29 33 33 34 35 39 41 42 42 43 44 45 46 48 xii 4 2 4 3 4 4 4 5 4 6 4 7 4 8 4 9 4 10 4 11 4 12 5 1 5 2 5 3 5 4 5 5 5 6 5 7 5 8 6 1 6 2 6 3 6 4 6 5 7 1 Le 7 3 1 4 7 5 7 6 1 1 7 8 7 9 8 1 List of figures Schematic representation of how an NPN transistor operates Characteristic curves for an NPN bipolar transistor Transistor as back to back diodes TO 92 pinout
194. p Flop 7490 Bi Quinary Counter 5 pin5 GND pin 10 5 5 pin 14 A 1 GND pin 7 13 74150 Multiplexer 4 74112 JK Flip Flop 49 GND pin 10 5 pin24 GND pin12 5 pin 16 15 GND pin 8 74121 Monostable 5 pin 14 GND pin 7 5 pin 16 GND pin 8 5 pin 16 GND pin 8 195 Appendix D Pinouts EEA ADCOBOX DAC080X Qr Qs Qs Q Qs Q Q 74138 3 to 8 Decoder Demux 5 pin 16 GND pin 8 197 Glossary of basic electrical and electronic terms ampere Basic unit of current 1 ampere 1 A 1 coulomb second angular frequency Rate of change of phase Measured in radians per second w 27f anode The negative terminal attenuation Decrease in voltage or current also implies power reduction capacitor Device used to store charge and energy The capacity of a capacitor is called the capacitance Capacitance C charge Q and voltage V are related by the equation Q CV cathode The positive terminal cathode ray tube A large vacuum tube in which the electron beam can be steered to create a visible pattern on a phosphorescent screen charge A fundamental property of some elementary particles Electrons have charge le and protons and holes have charge 1e where e 1 602 x 107 coulombs common Voltage reference point 0 V Also called ground compliance usually of a current source Range over which circuit performance is stable coulomb Unit of cha
195. pen to make a mistake in hooking up the circuit e Be careful to keep any exposed bits of metal from touching each other and making a short circuit Note that most of the exposed metal on 2 Of course the existence of other materials namely semiconductors for which the 7 V relationship is nonlinear makes electronics much more interesting and underlies the transformation of daily life brought about by electronics during the twentieth century 3 Tf you don t have a PB 503 breadboard find a 10 k pot on your breadboard if it has one otherwise you will have to purchase a separate 10 k pot 1 Equipment familiarization Table 1 2 Color code for nonprecision resistors 5 10 or 20 tolerance The resistance in ohms is the sum of the values in columns 1 and 2 multiplied by the value in column 3 plus or minus the tolerance in column 4 For example the color code for a 1 k resistor would be brown black red for 51 Q green brown black for 330 Q orange orange brown etc Stripe 1 2 3 4 tolerance Black 0 0 10 Brown 10 1 10 Red 20 2 10 Orange 30 3 10 Yellow 40 4 104 Green 50 5 105 Blue 60 6 10 Violet 70 7 107 Gray 80 8 108 White 90 9 10 Gold 5 Silver 10 None 20 Stripe 2 Me y Tolerance Stripe the breadboard screw heads for example has a low resistance path to ground e Ifyou accidentally connect power or ground to the potentiometer s center tap you can easi
196. plain what you see gt Given that the scope probe has an input impedance of 10 MQ estimate the power of this signal i e how much power is dissipated by the scope probe 95 7 Introduction to op amps Vout a 100 k at 10k Vin Vout 1 MQ b Fig 7 6 a Op amp voltage follower b voltage follower as the input stage to an inverting op amp circuit You can reproduce this effect more simply by touching the probe tip with your finger 60 Hz noise is pervasive throughout North America 50 Hz in Europe and is often the dominant background noise in elec tronic equipment gt Try amplifying this low power signal using the inverting amplifier circuit previously constructed Sketch the output and record your observations gt Now instead of driving the amplifier directly insert a voltage follower as shown in Fig 7 6 b Record the follower output as well as the amplifier output If the amplifier output saturates choose a smaller feedback re sistor to reduce the gain of the inverting amp Explain your observations 7 2 5 Difference amplifier Fig 7 7 shows the 741 configured as a difference amplifier with the output voltage equal to the difference of the two input voltages A difference am plifier is both an inverting amp and a noninverting amp An inverting amp is created if Vin is grounded whereas a noninverting amp is created if Vin_ is grounded If both inputs are connected to signals the differen
197. presence of a strong electric field no current 32 Hands on electronics flows Semiconductors such as silicon and germanium are somewhere in between The conductivity of a semiconductor can be enhanced through doping the deliberate inclusion of impurities within the semiconductor lattice Silicon for example has four valence electrons which are used to make covalent bonds with neighboring silicon atoms Phosphorus has five va lence electrons and boron has three In a silicon crystal if a silicon atom is replaced with a donor material such as phosphorus an extra valence electron becomes available that is loosely bound to the lattice If an acceptor material such as boron is substituted for silicon a hole appears in the electron structure of the lattice Doping silicon with a donor material creates an N type semiconductor whereas doping with an acceptor cre ates a P type semiconductor Note that despite their names these doped semiconductors are electrically neutral the extra electrons in N type ma terial are compensated for by the additional protons in the atomic nuclei of the donors while the missing electrons in P type are compensated for by the missing protons in the acceptor nuclei The extra electrons within N type material can move under the influ ence of an electric field Thus the dominant charge carriers are electrons i e N type material has negative charge carriers
198. pulous game designer how could you skew the ratio of heads to tails 12 Monostables counters multiplexers and RAM This chapter will introduce a variety of techniques that are important in sequential logic design Such designs often make use of pulses of various durations Sometimes a logic pulse of a given width needs to be formed in response to a particular input condition e g to standardize a pulse from a push button Monostable multivibrators are the usual solution In addition to monostables of a given logic family such as the 74121 122 123 etc there are also available the family of timer chips such as the 555 the latter are particularly useful when a long pulse of stable and reproducible width is needed In this chapter you will also explore counters and their uses in timing and addressing As an example of the use of an address counter you will store and retrieve information in a small memory chip Be sure to write down the circuit s schematic with pin numbers for ev ery circuit you build You will find the schematic especially useful should your circuit not work A simple review of the schematic will often re veal the source of the problem Futhermore a schematic is essential when debugging subtle errors Apparatus required Note 155 Breadboard oscilloscope 7400 NAND two 7490 and one 7493 counter 74121 or similar one shot 74150 multiplexer 7489 74189 or 74219 RAM chip two TIL311 displays
199. r s 1 W rating safe for its worst case power dissipation Caution These small diodes are easily damaged by overcurrent To be on the safe side do not let the forward current exceed 50 mA gt With a 1N914 or similar silicon diode forward biased as shown in Fig 3 5 increase the voltage across the diode starting from 0 V in steps of 100 mV and record the diode current in each case For the portion of the characteristic curve close to the origin the mi croamp range of the multimeter will be required to measure the forward current If you don t have a second meter available you can use your os cilloscope to measure the diode voltage gt Plot your results for J vs V on a linear scale do they seem qualitatively consistent with the functional shape of Eq 3 1 When unity is negligible in comparison with the exponential term of Eq 3 1 Eq 3 2 may be re expressed as E Ini InJ V 3 9 n nis 75 3 9 gt Plot InJ vs V Is lIn Z approximately linear in V How does its slope compare with e kT What value for n from Eq 3 1 is implied by your measured slope gt Now reverse the diode for a reverse voltage of 5 V what reverse current do you observe Is it consistent with the range of I expected for a silicon diode 39 3 Diodes S A mA COM VQ O A mA COM VQ O O QO a Ground Common b Fig 3 5 a Measuring the forward characteristic of a diode b When
200. r FETs MOSFETs In both types a conducting chan nel between the drain and source terminals is controlled by a voltage applied to the gate terminal The channel can be made of either N type or P type material Fig 5 1 N channel is more common since the conductivity of N type semiconductor in which electrons carry the current is higher than that of P type in which holes do 66 Hands on electronics N Channel P Channel P D S D S P G G D S D S G G N Channel P Channel JFET JFET Fig 5 1 Construction and circuit symbols of JFETs note that other variants of these symbols are also used The gate region of a JFET consists of material of opposite type to that of the channel thus the gate and channel form a diode In our preferred symbol for JFETs Fig 5 1 to distinguish the source from the drain the gate terminal is drawn at the source end even though the channel is physically spread out between the source and drain As for any diode the arrow on the gate symbol indicates the direction of forward bias However JFETs are normally used with the gate channel diode reverse biased In a JFET the channel conducts unless it is turned off by an applied reverse bias voltage between the gate and the channel As the reverse bias is increased more and more current carriers are repelled out of the channel until it is pinched off and the drain source current drops to zero see Fig 5 2 The voltage at which
201. r of which he designed a computer based on DTL integrated circuits Over more than twenty five years in experimental particle physics he has often been responsible for much of his experiments custom built electronic equipment He is the author or co author of over 150 scientific papers and one encyclopedia article and co editor of three books on heavy quark physics and related fields Dr Christopher G White is Assistant Professor of Physics at Illinois Institute of Technology He received his Ph D in Physics from the University of Minnesota in 1990 He has authored or co authored over 100 scientific articles in the field of high energy particle physics and his current research interests involve neutrinos and hyperons Dr White is an enthusiastic and dedicated teacher who enjoys helping students to over come their fear of electronics and to gain both confidence and competence xvii To the Reader Some of you may be encountering electronic circuits and instruments for the first time Others may have played around with such stuff if for example you were ever bitten by the ham radio bug In either case this sequence of laboratory experiments has been designed to introduce you to the fundamentals of modern analog and digital electronics We use electronic equipment all the time in our work and recreation Scientists and engineers need to know a bit of electronics for example to modify or repair some piece of equipment or to int
202. rect the drive signal to the push pull stage to compensate for the 2 Vgg gap gt First hook up the circuit of Fig 8 9 a to see crossover distortion in action This circuit is susceptible to noise so be neat and orderly and keep the leads as short as possible Use an audio frequency sine wave in the vicinity of 1 kHz Record the input and output waveforms how do they differ and why Rearrange the feedback loop to include the push pull driver inside it Fig 8 9 b and compare the input and output waveforms again What does the signal at the op amp output look like and why How much power is dissipated in the speaker assuming a sine wave of amplitude 4 V How does the peak current through the speaker compare with the 741 s maximum output current Sketch the op amp input the op amp output and the waveform at the speaker for both circuits and explain how the op amp eliminates crossover distortion Estimate the total power consumed by this circuit What is the maximum input amplitude that can be accurately reproduced at the speaker without clipping 111 8 More op amp applications See Vout Vin out 7 V PTEE Linear i V in ca Amplifier Pa out plifier pa 2 Amplifier Fig 8 10 Block diagram showing how to build an exponentiator a circuit that creates an output voltage equal to the input voltage raised to any desired power 8 3 Additional exercises The availability of log and antilog circuits allows
203. red a square wave in the previous chapter the scope s calibrator signal A square wave of amplitude Vo is a signal that oscillates back and forth between two voltage levels one at Vo and one at Vo spending 50 of the time at each level Note that the peak to peak voltage is twice the amplitude Vp p 2A A sine wave is a particularly important case because by Fourier de composition any periodic waveform can be represented as a sum of sine waves of various amplitudes and frequencies Most of AC circuit analysis therefore concerns itself with the response of circuits to sine waves 18 Hands on electronics Fig 2 1 Representation of an arbitrary periodic waveform with period T amplitude Vo and peak to peak voltage Vp_p A sine wave can be represented mathematically by V t Vo sin wt 2 2 If t is in seconds this describes a voltage with amplitude Vo changing sinu soidally in time at the rate of w radians per second The phase determines the voltage at t 0 V O Vosing 2 3 Now suppose such a voltage signal is applied to a capacitor for sim plicity we choose 0 i e at t 0 the voltage is zero Since we are assuming there is no resistance in the circuit there is no possibility of a voltage drop anywhere in the circuit Thus at any moment in time the voltage across the capacitor must equal the voltage out of the signal source To find the resulting current we can differentiate Eq 2
204. result is latched onto the output bus and a DONE pulse is issued pin 5 Connecting DONE to WR as shown in Fig 13 3 a puts the ADC into a free run mode in which the completion of one conversion initiates the next Once triggered the ADC will repeatedly digitize the input voltage difference To ensure free run status following power up WR may need to be brought low manually so connect WR to a debounced push button as well as to DONE The chip has two grounds called analog ground A GND and digital ground D GND In many applications the analog and digital grounds are kept separate to reduce the analog noise introduced by rapidly changing digital signals We will ignore these effects and use a common ground for both pin 8 and pin 10 The range for the input voltage difference is determined by the input voltage reference we are using Vcc A digital output of 00000000 should correspond to an input very close to zero volts while the output 11111111 should correspond to a voltage near Vcc We shall use single ended inputs so you should ground Vin A more complete explanation of the ADC080x s features can be found in the manufacturer s data sheets gt Connect an ADCO80x chip as shown in Fig 13 3 a Connect pins 1 2 7 8 and 10 to ground Connect pin 4 to ground using a 50 pF capacitor Place a 10 k resistor between pins 4 and 19 Connect pins 3 and 5 and add a connection to a push button Using the 1 k pot appl
205. rge 1 coulomb 6 241 x 10 8 e where e is the charge of the electron current Rate at which charge flows Defined as the amount of charge that passes through a given surface such as the cross section of a wire per unit time A convenient analogy is the rate at which water flows under a bridge or through a pipe Positive current flows from points of higher voltage to points of lower voltage Due to Benjamin Franklin s choice for the definition of positive charge this is opposite to the flow of electrons daraf Unit of inverse capacitance decibel Unit for specifying a voltage or power ratio on a logarithmic scale dynamic resistance Effective resistance of a nonlinear element typically a PN junction such as a diode or transistor junction farad Unit of capacitance 1 farad 1 F 1 coulomb volt The farad is a large unit com monly available capacitors range in size from a few picofarads to many thousands of microfarads feedback A design approach or situation in which an electronic signal communicates infor mation from the output of an electronic device or circuit to its input Positive feedback enhances a change at the output i e a growing output with positive feedback grows even larger while negative feedback counteracts a change at the output frequency domain AC circuit analysis approach that focuses on circuit response to sine waves vs their frequency 198 Hands on electronics gain Increase in voltage or current a
206. rks How does the hysteresis prevent oscillations gt Based on the component values used what do you predict for the com parator thresholds What is the predicted amount of hysteresis in volts How do these compare with your observations gt Record what you see as you vary the input amplitude Below some input amplitude the output stops switching At what amplitude does this occur and why 9 1 4 RC relaxation oscillator By adding an RC network to your Schmitt trigger construct a square wave oscillator as shown in Fig 9 4 Since a fraction of the output is fed back into both the inverting and noninverting inputs this circuit has both negative and positive feedback By connecting pin 1 to 15 V as shown you should get a symmetrical square wave output with little DC offset No input from the function generator is required the circuit should oscillate spontaneously 118 Hands on electronics Fig 9 4 RC relaxation oscillator using comparator The expected frequency of oscillation is 1 2RCn 1 f 9 2 gt Sketch the output waveform and explain how this circuit works Hint it operates by repeatedly charging and discharging the capacitor between the two threshold voltages of the Schmitt trigger gt What are the threshold voltages gt Why does the circuit oscillate spontaneously gt Derive Eq 9 2 and compare with the observed frequency 9 1 5 555 timer IC Nowadays one hardly ever builds a
207. rols an output current is called a transconductance amplifier The transconductance g for a given device is defined as the change in output current per change in control voltage and has units of ohm otherwise known as a mho To understand the operation of an NPN transistor in more detail it is con venient to consider the flow of electrons since electrons are the majority carriers in the N type regions Note that the flow of electrons is of course opposite in direction to the flow of conventional positive current As above 49 4 Bipolar transistors LSS e Free Electron on Depletion we Sy Electric Field Region Electric Field o Hole N type e e N type e s s o e s t a e e e e So e o s Collector 2 ee e ef Emitter s SAE S o j a bd Rte p le m Q e e ef s le o La s lightly doped bd heavily doped e Base 1 i B Vee Fig 4 2 Schematic representation of how an NPN transistor operates External bias Vos I voltages create an electric field which pulls electrons emitted into the base by the emitter across the base and into the collector This results seemingly paradoxically in a large flow of electrons through the reverse biased base collector junction a current that is easily controlled by small changes in base voltage The large hollow arrow represents the flow of electrons from the emitter to the collector the following descripti
208. rs 87 7 Introduction to op amps The 741C is rated for maximum supply voltages of 18 V and the recommended range is lt 15 V To be on the safe side before you begin to build your circuit turn on the breadboard power and adjust the power supplies to 15 V and 15 V Next turn off the power and insert the op amp into the breadboard straddling the central groove of a socket block with pins 1 4 toward the left and 5 8 toward the right Note that the pins are delicate and are easily bent or broken If they are too bent to plug into the sockets straighten them carefully preferably using needle nose pliers Run wire jumpers from the V pin to the 15 V bus and from the V pin to the 15 V bus Any point of your circuit that is to be grounded should be attached to the common or ground bus Note In the circuits shown below the pin numbers have been omitted It is good practice for you to write in the pin numbers yourself before hooking up the circuits to reduce the possibility of confusion Trying to work out pin numbers on the fly and keeping them in your head instead of writing them down is a common cause of errors in hooking up circuits Also note Even though the power connections are usually not shown on schematic diagrams of op amp circuits the positive and negative supplies must always be con nected or the op amp won t do anything 7 1 2 An ideal op amp For a hypothetical ideal op amp
209. rs instead of the counter decoder version discussed above The idea is to produce eight bits of which seven are 1s and one is a 0 and circulate them around an 8 bit shift register Connect each shift register output both to clock and to SET of a flip flop so that each flip flop is first set and then reset by the clock edge if the analog output is too big This simple approach might or might not work depending on the internal timing of the flip flop clock and SET are changing simulta neously the question is whether the SET signal goes away within the flip flop soon enough so as not to override the clock edge If it does not you can use the diode trick to delay the clock relative to SET The diode trick consists of adding a series diode to shift a digital signal in voltage thereby changing the time at which it crosses threshold 183 Further reading The following table indicates the sections or chapters in four popular textbooks where you can find additional background information for each chapter of our text Expt D amp H Barnaal H amp H Simpson 1 1 6 Al A2 1 thru 1 02 1 09 1 App C 1 11 1 32 12 01 2 2 33 Al 1 02 03 1 0709 2 3 App A 1 12 16 1 18 20 3 4 5 Al A4 1 17 1 25 28 4 4 8 A8 2 thru 2 13 2 15 16 5 5 8 A8 3 thru 3 09 6 6 8 A4 A5 A8 2 18 2 14 7 9 A6 4 thru 4 09 4 11 12 9 10 8 9 A6 4 09 10 4 14 4 19 20 10 9 10 A7 A1 Suppl 4 23 24 5 10 11 10 11 D1 D2 1 10 8 thru 8 06 8 08
210. rus P type N type Fig 3 1 Representation of a junction between P type and N type semiconductor material Free electrons from the N region will migrate into the P region combining with holes p e Free Electron gt Electric Field O Hole Electric Field Forward Biased Diode Circuit Reverse Biased Diode Circuit Fig 3 2 Diode circuit symbol and biasing see Fig 3 2 New holes are created within the P material as electrons jump from the semiconductor to the metal contacts At the junction the holes from the P type material meet electrons from the N type material and combine A PN junction thus allows current to flow easily in one direction but blocks current flow in the reverse direction For such a diode the current J flowing through the device is given approximately by PSI 1 3 1 where J sometimes called Jp or J is the reverse saturation current e is the electron charge V is the voltage across the junction n is an empirical constant between 1 and 2 k is Boltzmann s constant and T is the junction temperature in kelvin For simplicity we ll assume for now that n 1 This dependence of current on voltage is illustrated in Fig 3 3 34 Reverse Breakdown Hands on electronics Forward Current 8 mA 0 8 Vaiode Volts 0 2 Reverse Current HA Fig 3 3 Typical current voltage characteristics for germanium and silicon diodes note that the current scales in
211. s a DAC and comparator In our successive approximation circuit Fig 13 7 the eight bits are stored in four 74 dual D type flip flop chips The successive approximation algorithm consists of trying each bit in both the 0 and 1 states starting from the MSB and ending with the LSB Each bit starts out at 0 and is then set to 1 If the DAC output exceeds the analog input the bit is set back to 0 otherwise it is left as a 1 To accomplish this the circuit goes through a sixteen state cycle in order both to set and possibly reset each of the eight bits The sixteen state cycle is provided using a 191 four bit binary counter The 138 1 of 8 decoder routes clock pulses how many to each flip flop in turn The 311 comparator compares the DAC output with the analog input and its output is connected to the D input of each flip flop Note that the DAC080x is a current sinking DAC and its output thus becomes more negative as its digital input increases from 0 to 255 The connection shown thus provides negative feedback if the DAC output is too negative the currently addressed bit is set to 0 in order to raise the DAC output voltage and if the DAC output is too positive the bit is set to 1 in order to lower it Timing and control logic If you choose to undertake this exercise you should first spend some time understanding the timing cycle and drawing a complete timing diagram for the control logic shown in Fig 13 6 and the lower left ha
212. se as floating inputs will not work with CMOS gates With a 7486 quad two input XOR gate you can test two 4 bit binary numbers for equality 142 Hands on electronics gt Using all four XOR gates on the 7486 plus whatever additional gates you need design a circuit whose output indicates whether the two halves of the 8 bit level switch are set equal LED on if they are equal off if they are different You will find that this is quite cumbersome using NAND gates since equal ity corresponds to all four 7486 outputs being low But it becomes much simpler if you use OR gates such as the 7432 gt Record your schematic including pin numbers build your circuit and try it out Allow one or more inputs to float by leaving them unconnected Is your observation consistent with the general property of 7400 series TTL chips that floating input lines default to a high state This is a handy feature when testing circuits on a breadboard but it is good design practice not to rely on it to be certain of reliable operation and be maximally insensitive to noise if you are using a gate in a circuit you should connect all of its inputs either to high or low or to outputs of other gates gt Display the output with a logic indicator and verify that your circuit works for a few representative cases Record the input and output in each case 10 4 Additional exercises 10 4 1 7485 4 bit magnitude comparator This single chip does the wor
213. since CMOS logic levels satisfy the TTL input criteria To display a 4 bit hexadecimal number connect the digital signals for the four bits to the pins labeled DO D1 D2 D3 with D3 being the high order 2 bit Ground BI blanking input when high the display is blank and LE latch enable latches input when high Since you don t want to display a decimal point leave the DPL decimal place left and DPR decimal place right pins open If you wish to experiment with the decimal place LEDs be sure to use a current limiting resistor in series with the input pins See the TIL311 data sheet for additional information concerning these features gt Clock your counter from a debounced switch and confirm that it and the display both work What are the state table and timing diagram for the four outputs gt Try out the Ro and Ro inputs what do they do gt Add a second 7490 and TIL311 so that you can count from 0 99 Clock your circuit from a digital square wave at several hertz and verify that it works Save it for use in the following sections 12 3 2 Monostable multivibrator The object of this exercise is to design a circuit that generates a pulse of about 500 us duration To determine experimentally whether your one shot is functioning properly use its output to gate the clock to your two digit decimal counter i e present the counter with a stream of clock pulses only while the one shot is firing see Fig 12 3 T
214. sistor is small enough to bias the gate very near ground Quiescently the FET is thus in the saturation region with Ip determined by Jpss and Vp according to Eq 5 1 If the input voltage increases Vgs moves closer to zero the channel opens and Ip increases 72 Hands on electronics 15 2N5485 Fig 5 6 Source follower Thus Vout follows the source When Vin decreases the channel closes and Vout drops gt What is the DC offset at the output gt Measure the voltage gain You should see that the voltage gain is less than unity since the dynamic resistance of the source 1 g forms a voltage divider with Rs This effect was also present for the bipolar transistor but was much smaller due to the bipolar transistor s larger value of g Draw a diagram of this voltage divider gt From your observed attenuation derive a value for g and compare with that of a bipolar transistor at the same current You can improve the source follower by providing it with much higher load resistance Since an ideal current source would have infinite resistance a current source load is often used it can be constructed by adding another FET as in the clever circuit of Fig 5 7 Since we are using N channel JFETs it is actually a current sink Try it out gt Measure the voltage gain and the DC offset from input to output Note that if the two 2N5485s approximately match in their character istics not only is the voltag
215. sponse to a change in emitter current for example how the emitter voltage would differ if the emitter were driving a small load resistance as opposed to a large one To determine re we differentiate Eq 4 3 at fixed base voltage giving kT 1 Fe 5 e Ic 4 6 In addition there is the ohmic resistance of the emitter which is typically a few ohms Dynamic resistance of base On the other hand if we fix the emitter voltage we can find from Eqs 4 3 and 4 4 the dynamic resistance rpg to the emitter as seen at the base FBE e pe 4 7 This tells us how the base loads the circuit that is driving it We see that the base emitter junction appears to have a low resistance when viewed from the emitter end but appears to have a higher resistance by a factor B when viewed from the base end Some useful approximations Since at room temperature e kT 39 V in practice a reasonable ap proximation is 25 mV Fe d 4 8 Ic 25 mV ree B 4 9 Ic Since the emitter acts as a low impedance only a few ohms for typical collector current values its voltage hardly depends on the current flowing through it But the base acts as a high impedance so it is easy to apply a sig nal voltage to the base This comes about because the base current is smaller than the emitter current by the factor 6 which is of order 100 Although rge is only a few hundred ohms the factor 6 applies also to any resistor 54 Hands on e
216. square wave oscillator from an op amp or comparator since the 555 series of timer chips makes designing stable predictable oscillators easy Note that a 555 is not an op amp or comparator but an oscillator kit including two comparators among other items see Fig 9 5 The 555 can also be used as a timer as we shall see below The 555 is an eight pin IC powered from a positive voltage source The supply voltage can range from 4 5 to 16 V As with a comparator the output is digital with a high value near Vcc and a low value near ground The output sinks current while low and sources current while high up to 200 mA in either case Also as with a comparator the 555 output slew rate 119 9 Comparators and oscillators 555 Timer Threshold Output Stage comparator Flip Flop Discharge E comparator Fig 9 5 Block diagram for the 555 timer IC is high and the 555 can change states within 100 ns Refer to a 555 data sheet for additional details To see how the 555 works first examine the connections associated with the two comparators The top comparator output is high when the threshold input is greater than Vec and low otherwise The bottom comparator output is high when the trigger input is less than Vcc and low otherwise In general TRIGGER and THRESHOLD should be configured such that only one of the comparators is high at any given moment The outputs connect to a flip flop described in detail in
217. ssful design useful for sig nals from DC to beyond audio frequency though in recent years FET input op amps such as the LF411 have been gaining on the 741 in popularity It is available from most manufacturers of linear integrated circuits chips that produce an output proportional to their inputs as opposed to digital ICs whose outputs have typically only two states Each manufacturer has a different system of nomenclature for ICs e g National Semiconductor calls the 741 an LM741 Fairchild a A741 etc but the 741s made by different manufacturers are all electrically compat ible To add complication the 741 is available in various package styles and is rated for use in various temperature ranges The one we use is the 86 Hands on electronics offset null 741 op amp no connection top view inverting input V noninverting output input offset null Fig 7 1 Diagram of eight pin DIP 741 package showing pinout Often in addition to or instead of the notch at the pin 1 end of the package there is a dot next to pin 1 741C commercial temperature range 0 to 70 C in the eight pin mini DIP dual in line pin plastic package This package is convenient because the two rows of pins easily straddle the groove running down the center line of a breadboard socket block You can find the manufacturer s data sheet for the 741 on the web or in just about any electronic textbook or linear IC data book As shown on th
218. st less than 0 50 each in small quantities with the more complex chips ranging toward several dollars 10 1 1 Logic levels Digital chips employ two voltages to represent two possible states These voltages are called logic levels and can be used to represent the two states of Boolean algebra as well as the two digits of binary arithmetic There are three ways of referring to logic levels e true and false e zero and one and e high and low In TTL logic a voltage exceeding 2 V is called high while a voltage less than 0 8 V is called low To ensure noise margin TTL outputs are guaranteed to put out at least 2 5 V in the high state and at most 0 4 V in the low state see Fig 10 1 This means that even in the presence of up to 400 mV of noise an output low will be recognized as low by the input of the next logic circuit and similarly for high The comparable CMOS levels are 3 5 and 1 5 V for the inputs and 4 5 and 0 5 V for the outputs While TTL chips are always powered from a 5 V supply many CMOS chips are tolerant of supply voltages ranging from 2 to 6 V It is therefore convenient to reference CMOS logic levels to the power supply voltage Vcc The minimum input voltage interpreted as a CMOS high Vim equals 0 7 x Vcc while the maximum input voltage interpreted as a CMOS low Vi equals 0 3 x Vcc The output voltages Voy and Voy will vary with supply voltage as well The high low nomenclature is unambiguous since
219. t a square waveform whose low voltage level is near zero volts and whose high is near 5 V Use it to apply a signal to the input and measure the output slew rate i e the transition speed from high to low and from low to high How does the output transition speed compare with the transition speed of the input square wave gt Measure the input and output impedances and compare your results with your expectations The output impedance should be measured for both high and low output logic states using a pull up resistor to 5 V ora pull down resistor to ground as appropriate try a 330 Q resistor If you used a discrete component LED indicator you should disconnect it to avoid confusion or else figure out how to take it into account The inverter can be converted to a NAND gate with the addition of two more MOSFETs Do so as shown in Fig 10 9 Connect the output to a logic indicator gt Using logic switches verify the truth table gt Tie one input to 5 V and the other to a TTL square wave Measure the transition speed of the output gt Measure the output impedance with both inputs high as well as with both inputs low Compare these results with the values measured for the inverter Does the output impedance depend on the output logic level How does the output voltage level depend on the output load 140 Hands on electronics 10 3 3 CMOS NAND gate From your collection of chips select a 74HC00 quad NAND gate Referr
220. t at 25 kHz Change the input frequency and see if your prediction is correct gt At approximately what frequency will Eq 2 18 cease to predict the output waveform accurately Change the input frequency and test your prediction 2 6 Low pass filter Now switch from a 50 kHz square wave to a 50 kHz sine wave Since Eq 2 18 should still apply the output waveform should be the integral of a sine wave i e a cosine wave gt What does this imply about the phase shift between input and output Measure the phase shift 360 multiplied by the time Ar between the zero crossing of the input signal and the zero crossing of the output signal divided by the period or At 360 2 19 The cursors are useful here gt Is the measured phase shift consistent with your prediction Does the voltage across the capacitor lag or lead the current through it Explain 26 Hands on electronics The other way to analyze this circuit is as an AC voltage divider using Eq 2 13 with R2 replaced by the reactance of the capacitor Xc and Ry R gt replaced by the total impedance Z of the resistor and capacitor in series Since the voltage across the capacitor is 90 out of phase with the current through the resistor these add in Pythagorean fashion Xc Vout V Zz 2 20 X zye 2 21 R X 1 2 22 Vin J1 RCY We see that the attenuation Vout Vin depends on the frequency gt What attenuation do you observe at 50 kHz C
221. t flip flop an RS latch made of cross coupled NANDs an equally simple RS latch can be made from 146 Hands on electronics R S Q Qna H HJQ Q x HIL H H IH L L H H but note that the state after LL input condition is removed depends on which input signal goes high first if both go high simultaneously state is undefined Fig 11 2 Simple RS latch made of two input NANDs with state table NORs R and S refer to RESET and SET RESET is also known as CLEAR SET turns Q on while RESET CLEAR turns Q off Q is the opposite of Q except when both S and R are asserted Note on assertion level logic notation The inputs in Fig 11 2 are active low a low input forces a particular output condition while a high input does nothing We have therefore taken advantage of DeMorgan s theorem to write the circuit in terms of negative logic OR gates rather than blindly using the NAND symbol just because the 7400 is called a NAND gate by its manufacturer Since the OR gate with inverted inputs has the same truth table as the NAND gate it is just as good a symbol for 1 of a 7400 as the NAND symbol And it is actually better to use the OR symbol here since it makes the circuit s operation easier to see at a glance The use of DeMorgan s theorem in this way is called assertion level logic notation and it is a kind of hybrid between positive logic and negative logic the idea is always to choose the gate symbol th
222. t resistors have a simple linear relationship between the voltage across them and the current through them Ohm s law On the other hand e diodes have an exponential relationship between current and voltage Mathematically this may seem much more complicated than Ohm s law but we think you Il agree that the idea as just stated is simple enough it just takes some getting used to As we ll see an important consequence of the exponential characteristic is that diodes conduct much more readily in one direction than in the other This makes them ideally suited for rectification the conversion of AC into DC Apparatus required Breadboard oscilloscope one or two multimeters one 1N914 or similar silicon signal diode one 1N4001 or similar 1 A silicon rectifier diode one 100 Q and one 10 k 1 W resistor one 1 k 2 W resistor power transformer with 12 6 V r m s output on each side of the center tap one diode bridge element one 100 pF electrolytic capacitor and one 1000 pF electrolytic capacitor 3 1 Semiconductor basics 31 Current will flow through a material provided that there are charge carriers free to move and an electric field to move them Conductors such as copper have lots of charge carriers electrons ready to move in response to the slightest electric field Insulators such as diamond possess very few free charge carriers all the electrons are tightly bound to the crystal lattice so that even in the
223. tan wRC 2 34 Note as expected that at high frequency the voltage division ratio goes to unity in the first case and to zero in the second case while the phase shift goes to zero in the first case and to 90 in the second Also in both cases the breakpoint frequency is the point at which the two terms in the f fo f fo t gt fo Vout IR Vout IR Vout IR v N A oC Vin L i oC Vin oo Vin a b Fig 2 6 Right triangles depicting the relationships among input voltages always represented by the hypoteneuse of the triangle and capacitor and resistor voltages for a high pass and b low pass RC filters In each case the center diagram shows the isosceles triangle representing the case f fo the triangles on the left are for a frequency well below fo and those on the right for a frequency well above fo 30 Hands on electronics square root are equal RC 1 2 35 fo 2 36 IU 1 g 2 37 27 RC These relationships are all illustrated in Fig 2 6 which shows for low and high pass filters how the phase and magnitudes of the voltages across the resistor and capacitor are related for a fixed input voltage in three frequency regimes f fo and frequencies that are well below and well above fo See Appendix C for further discussion of frequency domain analysis of RC circuits 3 Diodes In this chapter we will explore semiconductor diodes and some circuits using them We ve seen tha
224. tate correctly gt In your own words and based on your observations explain the operation and features of the 74373 11 5 Flip flop applications 11 5 1 Divide by four from JK flip flops Ripple counter Cascading two toggling flip flops makes a divide by four circuit otherwise known as a two bit counter gt First make the two bit asynchronous or ripple counter shown in Fig 11 7 This circuit is asynchronous in that it does not have acommon clock signal for all flip flops Clock it from a push button while looking at the two Q outputs with logic indicators and verify that it divides by four i e that the output square wave changes state at 1 the frequency of the input clock Write down its state diagram gt Clock it with a square wave and look at the clock and the outputs on the scope To see the binary counting pattern watch clock and Qo then Qo and Q always triggering on the slower waveform Write down the Fig 11 7 Divide by four ripple counter 152 Hands on electronics EEE Fig 11 8 Synchronous divide by four counter timing diagram and label the states with their numeric values 0 through 3 interpreting Qo as the low order bit and Q as the high order bit of a 2 bit binary number gt Turn the scope s sweep rate up until you can see the ripple Qo and Q don t change at the same time Explain why not Be sure to look at both edges of Q4 Synchronous counter Now configure the cir
225. ter 157 frequency domain 15 101 function generator 2 13 gain common mode 78 gain differential 77 gate current 66 gate exclusive OR 141 NAND 140 OR 142 XOR 141 gate channel diode 66 golden rules op amp 90 ground virtual 93 168 ground clip 10 grounded emitter amplifier 59 half power frequency 26 hexadecimal 158 164 hexadecimal display TIL311 158 high logic level 126 hysteresis 116 170 IC digital 85 linear 85 ideal ammeter 39 ideal op amp 87 ideal rectifier 36 ideal voltmeter 39 impedance input 45 output 45 measuring 46 indicators LED breadboard 137 inductance 19 inductive reactance 19 inductor 19 information analog 167 digital 167 input bias current 94 input impedance 45 input offset voltage 78 91 integrated circuit digital 85 linear 85 integrator 15 24 103 active 103 107 op amp 103 107 internal state 143 146 149 162 inverter 60 141 149 inverting amplifier 58 88 168 op amp 88 168 JFET 65 JK flip flop 148 junction diode 32 junction summing 93 169 latch RS 145 153 LED 60 LED indicators breadboard 137 level switches breadboard 137 138 LF398 SHA 177 light emitting diode see LED linear region FET 68 logarithmic amplifier 105 logarithmic search algorithm 171 202 Index logic assertion level 127 146 digital 125 diode 131 multiplexer 162 negative 127 positive 127 sequent
226. the capacitor see Fig 2 5 Drive the circuit with a 50 Hz square wave gt What waveform do you see at the output What are the input and output amplitudes You can think of the shape of the output in terms of the exponential RC charging discharging curve with f 1 RC or you can think of it as an approximation to the derivative of the input signal Mathematically the derivative of an ideal square wave would be infinite at the voltage steps and zero in between but of course an electrical signal can never be infinite In this circuit the voltage spikes are limited in size to twice the input amplitude Using Eq 2 16 Vaut IR 2 24 dQ SR 2 25 ay 2 25 d Vin Vou pe o 2 26 dt dV RCW 2 27 dt where the approximation is again valid when Vou lt Vin So indeed the circuit puts out an approximation to the time derivative of the input signal You can see why the approximation of Eq 2 27 breaks down in the case of a square wave since at the rising and falling edges of the square wave Vout gt Vin gt What does Eq 2 27 imply if the input is a triangle wave Try it out and compare quantitatively with what you expect gt What does Eq 2 27 imply if the input is a sine wave Try it out and com pare quantitatively with what you expect Sketch the output waveform Vi Vout C R Fig 2 5 High pass filter or voltage differentiator 28 Hands on electronics If you are surprised at all the w
227. the full timing sequence on the oscilloscope Trigger the scope on the output of the second flip flop and observe each of the other signals as you repeatedly issue START CONVERT Verify that your timing diagram is correct Complete ADC circuit Now add the rest of the circuit Use the breadboard logic indicators to display the data bits Attach the RESET input to the other debounced push button Measure the DC analog input voltage Vin with a digital voltmeter Try several voltages over the full range and make a graph of your results 180 Hands on electronics E 5 15 300 pF a as EL 76543210 ae 74138 Fig 13 7 8 bit successive approximation ADC How good is your ADC Is it linear What is its zero offset the number it puts out for Vi 0 and what is its slope constant volts per output count What is its least count the voltage change corresponding to one ADC count What is its full scale voltage Try raising the clock frequency At what frequency does it stop working Does this make sense What do you think limits the conversion speed of this circuit Illustrate your answer with the relevant timing diagram Will this ADC always work correctly the first time after power is turned on Why or why not 181 13 Digital lt gt analog conversion I Simpler version of control logic You might want to build and analyze a simpler version of the control logic using parallel output shift registe
228. this occurs is called Vp or Vesvorr Note that the drain gate and source of an FET play similar roles to the collector gate and emitter respectively of a bipolar transistor Unlike the bipolar case the source and drain are roughly interchangeable and it is possible for an FET to be used backwards 5 1 1 FET characteristics The simplest way to think of FET action is as a voltage controlled current source i e the drain current Ip is approximately constant for a given gate source voltage Vgs depending only slightly on the voltage Vps between the drain and source Since the gate channel diode is normally reverse biased the gate current is extremely tiny typically nanoamperes so that for all 67 5 Transistors Il FETs Nes ae Drain Gate Source ee a a Gate i Vas Vos d H x Vas co Drain Gate Source s i b Gate Ves Vos F fifili T Fig 5 2 Schematic representation of JFET operation a gate channel diode slightly reverse biased b gate channel diode highly reverse biased Vgs gt Vp so that channel is pinched off b Saturation Region 0 5 10 15 20 Vos Volts Fig 5 3 Idealized common source characteristic curves for a JFET practical purposes the drain and source currents are equal Jp Is The voltage controlled current source behavior occurs as long as
229. tor 68 Em 48 transformer 40 transistor 48 transistor field effect 65 transistor junction 47 transistor simple model 51 transistor action 48 transistor current source 59 transistor model Ebers Moll 52 transistor saturation 68 transition speed 126 tri state 149 150 tri state output see output three state trigger Schmitt 116 triggering negative edge 147 149 157 positive edge 147 true logic level 126 truth table 140 141 143 146 204 Index TTL 125 TTL families 128 133 TTL history 128 133 TTL ICs powering 136 TTL logic levels 126 two bit counter 151 156 universal logic function 140 virtual ground 93 168 voltage peak to peak 17 quiescent 57 threshold 113 voltage comparator 113 voltage divider 15 22 23 26 voltage droop 43 voltage follower 94 voltage regulation 44 voltmeter ideal 39 word addressing 163 XOR 141 XOR gate 141 Zener diode 35 123 zero 126
230. tors and wires when done To measure the differential voltage gain ground one input while applying a 1 kHz sine wave of amplitude 1 V or less at the other input It shouldn t matter which input you ground If you re curious try it both ways and see if you get equal gains gt Measure the differential voltage gain gt Explain why it doesn t matter which input is grounded when measuring the differential voltage gain gt Estimate the CMRR for this circuit gt What is the input impedance at each input 7 3 Additional experiments 7 3 1 Current source An ideal current source would maintain a constant current through the load regardless of load resistance Try the op amp current source of Fig 7 8 Vary the load pot as you measure the load current with a digital multimeter and the load voltage with a multimeter or scope what do you observe gt Explain how this circuit works use diagrams and equations as necessary gt What should the current be and why gt What is d dV What is the compliance output voltage range over which d dV is small of your current source gt Compare the performance of this op amp current source to the transistor current sources you built previously 98 Hands on electronics 15 Fig 7 8 Op amp current source 7 3 2 Noninverting summing amp with difference amplifier This circuit is fun to build and to observe in action It also serves as an excellent demonstration
231. tput signals do you observe now for a common mode input What is the common mode gain now It should be very much smaller than previously if the output signal is so small that you have trouble measuring it you can at least set an upper limit on it and on the common mode gain Save your three transistor differential amplifier for use below 6 2 Op amps and their building blocks An operational amplifier is a differential amplifier with a single ended output and as high a differential gain as possible typically gt 10 Op amps are manufactured as integrated circuits They are typically used with DC coupling and with negative feedback from output to input Their internal design includes level shifting circuitry so that the single output is at O0 V if the two input voltages are equal 6 2 1 Current mirror To achieve high gain in op amps the emitter resistors are typically omitted and the collector resistors are replaced by current sources A current mirror is a convenient configuration for this purpose Build the PNP current mirror of Fig 6 3 The current out of Q4 pro grams an approximately equal current out of Qs as follows since Q4 s collector is connected to its base it is held at a Vgg drop below the positive supply This determines the current out of Q4 by Ohm s law applied to R 2 To set an upper limit assume that the output signal equals the precision of your measurement 80 Hands on electronics 15
232. two VPO610L and two VNO610L MOSFET transistors three 2N3904 transistors three diodes one LED one red LED optional 74HC00 7432 7485 7486 TTL or TTL compatible logic chips logic switches and logic displays 10 1 Digital logic basics In this section we introduce the 7400 series of CMOS and TTL digital logic chips Unlike the analog ICs you ve used up to now which can output any voltage within some range determined by the power supply voltages digital logic ICs employ only two ranges of output voltages referred to as logic levels about which more below These levels can be used to represent true or false logical conditions or the zero and one of binary arithmetic The 7400 series is not the only logic series nor are CMOS and TTL the only types of logic circuitry however they are the most commonly used Other logic families include the CMOS 4000 series and the ECL 125 126 Hands on electronics emitter coupled logic 10 000 and 100 000 series Each logic family has its own logic levels speed and recommended supply voltages The integrated circuits you will be using now are much more specialized than the general purpose 741 op amp and 555 timer They feature much higher bandwidth with typical transition speeds of order volts nanosecond in contrast to the volts microsecond slew rate of the 741 While greater complexity often means higher cost the basic chips in the 7400 families such as the 74HC00 74LS00 and 74ACTOO co
233. uations Suggestion You may want to skip the next section for now and use these rules to analyze the circuits of Figs 4 5 4 7 and 4 8 described in sections 4 2 2 4 2 3 and 4 2 4 Then come back and study the next section 4 1 3 Ebers Moll transistor model To see why the simple picture just described is valid we next consider the Ebers Moll model which is based on the physical description in section 4 1 and provides a reasonably good description of transistor action In this model the amount of collector current that flows is determined by the amount of forward bias that is applied to the base emitter diode We thus have Ic l c 1 4 3 As with Eq 3 1 Z is the reverse saturation current In practice the expo nential usually dominates and the 1 can be neglected Also as mentioned above the base current is related to the collector current by Ic 4 4 2 4 4 Iz Dynamic resistance of emitter Since the emitter current equals the collector current to a good approxima tion Eq 4 3 also detemines the emitter current We can thus use it to derive a useful expression for the dynamic resistance re of the emitter Recalling the definition of dynamic resistance re is the partial derivative of emitter 53 4 Bipolar transistors voltage with respect to emitter current _ OVE aye The dynamic resistance tells us how for fixed base voltage the emitter Fe 4 5 voltage would change in re
234. ue 99 7 Introduction to op amps function generator Summing Output Ry Ro Rg 10 kQ or similar 10 k pot CMRR Adjustment 10 MQ Fig 7 9 Fancy summing circuit Amp 1 is a voltage follower used to buffer the 60 Hz pickup on a wire wrapped around an AC power cord Amp 2 is a noninverting summing amplifier with unity gain Amp 3 is a difference amplifier with an adjustment to maximize the CMRR amplifier output Be sure to switch your trigger source back to the appro priate input channel Try changing the input frequency Replace the 60 Hz AC line signal at the noninverting input of the difference amp with the output from the function generator Observe how the output changes gt Explain how this circuit works using diagrams and equations as needed Explain why the summing amp isn t inverting and why it has unity gain gt Sketch the inputs and output of the summing amp for a function gener ator frequency near 60 Hz Why doesn t the output have a well defined amplitude gt Sketch the inputs and output of the difference amplifier How does the output change when the inputs are switched gt Is the output inverted with respect to the original inputs If so why If so what could you change to make the output of the difference amp noninverted with respect to the original inputs i More op amp applications In Chapter 7 we studied some of the basic properties of operational ampli fiers T
235. uits 17 2 1 2 Types and values of capacitors 19 vi Contents 2 2 Review of current voltage and power 2 2 1 Destructive demonstration of resistor power rating 2 3 Potentiometer as voltage divider 2 3 1 DC voltage divider 2 3 2 AC voltage divider 2 4 RC circuit 2 5 RC circuit as integrator 2 6 Low pass filter 2 7 RC circuit as differentiator 2 8 High pass filter 2 9 Summary of high and low pass filters 3 Diodes 3 1 Semiconductor basics 3 2 Types of diodes 3 3 Rectification 3 4 Diode action a more sophisticated view 3 5 Measuring the diode characteristic 3 6 Exploring rectification 3 7 Input and output impedance 4 Bipolar transistors 4 1 Bipolar junction transistor basics 4 1 1 Basic definitions 4 1 2 Simplest way to analyze transistor circuits 4 1 3 Ebers Moll transistor model 4 2 Experiments 4 2 1 Checking transistors with a meter 4 2 2 Emitter follower 4 2 3 Common emitter amplifier 4 2 4 Collector as current source 4 2 5 Transistor switch 4 3 Additional exercises 4 3 1 Darlington connection 20 21 22 23 23 24 24 25 27 28 28 31 35 36 37 38 40 45 47 47 50 51 52 54 54 55 57 59 60 61 61 vii Contents EEE 4 3 2 Push pull driver 4 3 3 Common base amplifier 5 Transistors Il FETs 5 1 Field effect transistors 5 1 1 FET characteristics 5 1 2 Modeling FET action 5 2 Exercises 5 2 1 FET characteristics 5 2 2 FET current source 5 2 3 Source follower 5 2 4 JFET a
236. ury Although discrete i e individually packaged transistors are now used mainly in special situations e g where high power or speed is required since transistors form the basis of a large class of integrated circuits an understanding of how they work remains valuable This will be the subject of the next few chapters This chapter will introduce you to some basic bipolar junction transistor circuits Apparatus required Breadboard oscilloscope two multimeters 2N3904 and 2N3906 transis tors red light emitting diode LED 1N914 or similar silicon signal diode two 330 Q two 10 k and one each of 100 Q 1 k 3 3 k 22 k and 100 k 1 W resistors 1 pF capacitor 4 1 Bipolar junction transistor basics 47 Why and how transistors work is a bit subtle and can easily confuse the beginning student but it is something you must master Study the following description carefully and compare it with the descriptions in other books You may also want to re read both our description and others after you ve had some experience building and analyzing transistor circuits If you want more of the background detail on semiconductor physics good places to look are Simpson s Introductory Electronics for Scientists and Engineers or any textbook on modern physics A bipolar junction transistor consists of two PN junctions sandwiched very close together within a single crystal of semiconductor Fig 4 1 a 48 Hands on electronics
237. use M instead of w A 10 millifarad cap would be labeled 10000M A small capacitor that says just 10 on itis 10 picofarads The other important number is the maximum operating voltage which is usually printed on the capacitor if there is room 20 Hands on electronics Some small capacitors are labeled like resistors either with a color code or with numbers that mean the same thing The first digit of this capacitance code is the tens the second is the ones the third is the power of 10 and the units are picofarads This is sometimes ambiguous for example a capacitor that says 470 could be 470 pF or 47 x 10 47 pF Usually the clue is the presence of a letter following the capacitance code that indicates the tolerance J for 45 K for 10 M for 20 etc so that 470 K means 47 pF 10 whereas just 470 means 470 pF Note that there is no ambiguity if it says 471 since normal capacitors are not manufactured with enough precision to warrant a third significant digit the 1 must be the power of ten When in doubt you can always check it out by putting it in an RC circuit with a known R value and measuring the time constant see below or by plugging it into a capacitance meter if you have one 2 2 Review of current voltage and power Before we get started on RC circuits let us briefly review power dissipation and component ratings you need to understand these to avoid dam
238. ut and shunt resistors Ri Rs 8 7 2 105 8 More op amp applications Since the shunt resistor limits the circuit s low frequency gain Eq 8 6 is valid for input frequencies greater than 1 8 8 27 R C Se T For input frequencies less than f the performance of the circuit approaches that of an inverting amplifier with voltage gain hea 8 9 8 1 3 Logarithmic and exponential amplifiers By using a diode as the input or feedback element we obtain a circuit that takes the logarithm Fig 8 6 or exponential Fig 8 7 of its input signal For the log amplifier we can analyze the circuit performance as follows the analysis of the exponential amplifier is left as an exercise Vout Fig 8 6 Op amp logarithmic amplifier Rg op amp Vout Fig 8 7 Op amp exponential amplifier 106 Hands on electronics The current Ip through the feedback element equals the input current J which is determined by the input voltage Vin V k i 8 10 We can relate this to the output voltage Vout using the exponential diode current voltage law Tp I eT _ 1 8 11 The minus sign in the exponential reflects the fact that the anode of the diode is connected to virtual ground thus for Ip positive Voy is neg ative The constant n has been introduced since as we saw in Chapter 3 the slope of the exponential for a silicon diode is not quite as steep as e kT one finds experimentally
239. vided by the scope on a metal contact labeled probe comp or something similar often located near the lower right hand corner of the display screen 10 Hands on electronics eS Note that a leg folds down from the bottom of the scope near the front face This adjusts the viewing angle for greater comfort when you are seated at a workbench so we recommend that you use it 1 3 1 Probes and probe test Oscilloscopes come with probes cables that have a coaxial connector sim ilar to that used for cable TV on one end for connecting to the scope and a special tip on the other for connecting to any desired point in the circuit to be tested To increase the scope s input impedance and affect the cir cuit under test as little as possible we generally use a 10X attenuating probe which has circuitry inside that divides the signal voltage by ten Some scopes sense the nature of the probe and automatically correct for this factor of ten others such as the TDS210 need to be told by the user what attenuation setting is in use As mentioned above your scope should also have a built in calibrator circuit that puts out a standard square wave you can use to test the probe see Fig 1 4 The probe s coaxial connector slips over the CH 1 or CH 2 input jack and turns clockwise to lock into place The probe tip has a spring loaded sheath that slides back allowing you to grab the calibrator signal contact with a metal
240. w turning off the outputs of all but one chip The chip accepts input data and puts out output data only when ME low Therefore be sure to ground ME gt Hook up the counter s outputs to the address lines of the RAM and display the output data with your second TIL311 Connect the data inputs and WE to level switches gt Use the address counter and the WRITE ENABLE switch to program your memory to any desired sequence of hex digits be sure to record what sequence you choose If you apply some ingenuity you can spell out messages using the letters A F plus I 1 and O 0 e g FEED BOB A DIODE Then clock the address counter with a digital clock at a 165 12 Monostables counters multiplexers and RAM LSS frequency of a couple of hertz and watch your message appear Record the complete circuit diagram with pin numbers and explain how this circuit works gt How could you use the 150 mux to shorten the sequence to any desired fraction of the sixteen addresses How could you use it to insert blank spaces between words 13 Digital lt gt analog conversion In this chapter we will study simple techniques for generating and read ing voltage or current levels i e converting between analog voltage or current and digital binary number information The availability of high speed easy to use inexpensive digital analog and analog digital con verter chips has dramatically changed the way audio and video information ar
241. we would need to take into account the inevitable small differences among the high and low levels of the counter outputs We shall not worry about these refinements since it is our intention here merely to illustrate the basic idea of D A conversion The output should be a fifteen step staircase waveform Fig 13 1b with each step having approximately the same height To see a stable dis play of the waveform you can trigger the scope using the falling edge of the MSB gt What full scale output voltage do you expect i e when the counter is at 15 in decimal or 1111 in binary What do you observe gt Is the staircase rising or falling Why is this What simple change can you make to reverse the direction of the staircase gt What are the output voltages corresponding to states 4 5 6 7 and 8 of the counter Measure the four resistances and the high and low voltage levels of the four counter outputs Q9 Q3 and explain each DAC output voltage gt Write down a complete circuit diagram with pin numbers Explain in your own words how this circuit works Despite the common misconception that modern electronics is strictly digital analog electronics is still going strong For all practical purposes our everyday world is analog The digital representation of any waveform music for example is only an approximation To smooth out the discon tinuities of digitized waveforms requires analog electronics 170 ess Hands on electronics
242. y a variable voltage between 5 V and ground to pin 6 Connect pins 11 18 to LED logic indicators Connect pin 20 to 5 V power and leave pin 9 unconnected gt Adjust the input voltage and observe the digital output What measured input voltage corresponds to the binary output 00000001 What mea sured input voltage corresponds to the binary output 11111110 Measure several other input voltage values and plot the input voltage versus dig ital output Is the plot linear What is the input range and how does the ADC respond to small excursions outside this range not less than ground and not more than Vcc With what precision does the ADC measure the input voltage 174 Hands on electronics EEE gt Estimate the conversion time by looking at pin 5 with the oscilloscope Conversion time is the amount of time an ADC requires to digitize an input voltage What is the sampling rate Does the conversion time depend on the input voltage Taking into consideration the value of the external RC network does the measured sampling rate agree with your expectations If not why not Hints parallel capacitors add linearly and some small stray capacitance is common on breadboards such as the PB 503 gt Observe sketch and explain the waveforms at pins 4 and 19 Replace the 50 pF capacitor with a 100 pF capacitor Explain what happens to the waveforms What happens if you remove the 100 pF capacitor completely i e do not use any external cap
243. y recall from your general physics that it obeys the equation V t Vow C 2 14 where t 0 corresponds to a rising or falling edge of the square wave Show that the time to fall to 37 of the peak value i e V t 0 37 Vo is the time constant RC and determine RC using the scope you should find your oscilloscope s cursor feature useful here Be sure to set the time and voltage scales sufficiently sensitive to yield an accurate measurement what settings should you use and why Based on the nominal component values what do you predict for RC Is your measurement consistent with this prediction What are the tolerances of the components you are using does this explain any discrepancy 2 5 RC circuit as integrator Now switch the function generator frequency to 50 kHz Observe what hap pens to the output waveform s shape and amplitude This can be explained 25 2 RC circuits S74 quantitatively from Eq 2 1 Vout t oo 2 15 oh a 2 16 Vin ER Vout lt f eat 2 17 1 t FG ants 2 18 where Vout is the voltage across the capacitor and the approximation is valid as long as Vou lt Vin gt What does Eq 2 18 predict when Vj is a constant as it is during half of each period of the square wave Carefully measure and sketch the output waveform Compare your observations with your expectations based on Eq 2 18 and explain your results gt What output amplitude would you expec

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