Tektronix 5A22N User's Manual
Contents
1. Photographs of the resultant display A composite waveform of a desired signal square wave with an interfering line frequency component is applied to the Input NOTE The waveform of the signals applied to the alone The interfering signal sine wave is also applied to the input connector input connectors will appear inverted when viewed Fig 1 1 Three examples of differential applications Tektronix P6023 probes for differential measurement This probe type does not have the coding feature to be discussed later a Connect one probe for DC coupled single ended input Obtain a triggered display of an appropriate square wave such as that from a calibrator or square wave generator Adjust the probe DC Atten Calibration control for correct deflection sensitivity then com pensate the probe square wave response using the AC Fine Comp adjust and the AC Coarse Comp adjust if necessary 1 6 b Connect a second probe for DC coupled operation Apply the square wave to both probes at 100 volts peak to peak Free run the sweep and adjust the DC Atten Calibration of the second probe for maximum low frequency cancellation minimum signal amplitude or elimination of the two trace appearance c Adjust the AC Fine Comp and AC Coarse Comp of the second probe to minimize the if necessary amplitude of the differential2. J di SAZ2N Differential Amplifier 5A2ZN SECTION 1 OPERATING INSTRUCTIONS instrument Description The 5A22N Differential Amplifier is a high gain differential amplifier plug in unit for use with Tektronix 5100 Series Oscilloscopes The unit features high sensitivity with direct coupled inputs high common mode rejection and variable DC offset An illuminated knob skirt provides deflection factor readout The unit has a maximum bandwidth capability of DC to one megahertz with selectable high and low frequency limits for increasing the signal to noise ratio at low frequencies CONTROLS AND CONNECTORS This is a brief description of the function or operation of the front panei controls and connectors More detailed information is given under General Infor mation DISPLAY Applies and removes logic levels to the oscilloscope system to enable or disable plug in operation Switch is functional only when plug in is operated in one of the vertical plug in com partments POSITION Positions display HF 3 dB Allows reduction of the upper bandwidth frequency limit to increase the signal to noise ratio for low frequency applications Allows lower bandwidth frequency to be increased thus reducing bandwidth and increasing the signal to notse ratio Also low frequency drift can be reduced by restricting frequency response When AC coupled the lower bandwid
3. AC CAPACITIVE COUPLED At least 80 dB at 5 kHz and above decreasing to 50 dB at 10 Hz DC Offset Range At least and 0 5 V from 10 uV div to 50 mV div At least and 50 V from 100 mV div to 5 V div Input RC 1 MO within 0 1 paralleled by 47 pF Overdrive Recovery Unit recovers to within 0 5 of the quiescent level in 5 us after overdriving signal has been applied for 1 s Maximum Input Gate Current 100 pA 100 uV depending on external loading at 25 C Maximum Safe Input Voltages DC DIRECT COUPLED 10 V DC peak AC from 10 uV div to 50 mV div 350 V DC peak AC from 100 mV div to 5 V div AC CAPACITIVE COUPLED 350 VDC 10 V peak AC from 10 uV div to 50 mV div with coupling capacitor precharged 350 V DC peak AC from 100 mV div to 5 Vidiv DC Stability DRIFT WITH TEMP 100 VC Displayed Noise 20 uV or less measured tangentially at full bandwidth DC to 1 MHz with 25 Q source resistance l 1 7 Operating Instructions 5A22N REPACKAGING FOR SHIPMENT If the Tektronix instrument is to be shipped to a Tektronix Service Center for service or repair attach a tag showing owner with address and the name of an individual at your firm that can be contacted complete instrument serial number and a description of the service required Save and re use the package in which your instrument was shipped If the original packaging is unfit for use or not available repackage the instrument
4. Signals applied to the input connector will be inverted A similar polarity relationship exists for differentially applied signals but it pertains to the direction of voltage change at one input with respect to the other rather than with respect to chassis potential Deflection Factor The amount of trace deflection produced by a signal is determined by the signal amplitude the attenuation factor if any of the probe the setting of the VOLTS DIV switch and the setting of the Variable control The calibrated deflection factors are VOLTS DIV switch only when the Variable control is rotated fully clockwise into the detent position indicated by the Fe u ener i i i em amplified and displayed while the common mode signals common in amplitude The range of the Variable control is at least 2 5 1 it provides uncalibrated deflection factors covering the full J range between the fixed settings of the VOLTS DIV switch The control can be set to extend the deflection factor to at least 12 5 volts division To reduce noise at higher frequencies and drift at lower frequencies and obtain a more usable display when the VOLTS DIV switch is set to the more sensitive positions reduce bandwidth with LF and HF 3 dB switches Voltage Comparison Measurements Some applications require deflection factors other than the fixed values provided by the VOLTS DIV switch One such applic
5. at the input FET gates in precisely the same form A difference of only 0 01 in the attenuation factors of the input attenuators may reduce the rejection ratio to 10 000 1 Likewise any difference in source impedance at the two points in the source under test will degrade the rejection ratio Attenuator probes which do not have adjustable R and C may reduce the rejection ratio to 100 1 or less swapping probes may improve the rejection ratio Outside influences such as magnetic fields can also degrade the performance particularly when low level signals are involved Magnetic interference may be minimized by using identical signal transporting leads to the two inputs and twisting the two leads together over as much of their length as possible Voltage Probes In general probes offer the most convenient means of connecting a signal to the input of the 5A22N Tektronix probes are shielded to prevent pickup of elec trostatic interference A 10X attenuator probe offers a high input impedance and allows the circuit under test to perform very close to normal operating conditions See your Tektronix Inc catalog for characteristics and compatibility of probes for use with this system Differential Measurement The following adjustment procedure is recommended when preparing to use two 1 5 Operating Instructions 5A22N Double exposure photographs of the waveforms applied to the and pe connectors
6. attenuator When the fink is removed the attenuation ratio fs affected causing the deflection factors in this range to be incorrect To determine the deflection factor check the deflection with an input signal of known amplitude The signal source impedance is an important factor since gate current will produce a DC offset For example a 100 picoampere gate current through 10 megohms produces a one millivolt offset which may result in significant error where small voltages are of concern The high frequency response will also depend upon the signal source impedance since various shunt capac itances between the source and the input gate must charge and discharge through that impedance Gate Current Compensation The leakage current associated with the gates of the input FETs may be as high as 100 picoamperes This leakage current will produce an offset voltage which at the higher input sensitivities is not acceptable For example 100 picoamperes through a one megohm input resistance to ground produces an offset voltage of 100 microvolts which could drive a display off screen at 10 microvolts per division To compensate this effect the gates of the input FETs may be adjusted to zero volts by returning R120 and R126 through potentio meters R121 and R127 to a slightly negative supply voltage Display Polarity Single ended signais applied to the input connector produce a display in phase with the input signal
7. Calibrator loop through a test lead or 1X probe to the input connector 7 For DC coupled single ended operation release the input GND button The display should be a four division square wave with the bottom of the display at the reference established in step 5 Rotate the Variable Volts Div control counterclockwise out of its detent position observing reduction of the display Return the Variable contro to the detent CAL position 8 For AC coupled single ended operation re position the display with the POSITION control to place the bottom of the display at the graticule centerline 9 Push in the AC button and note that the display shifts downward about two divisions to its average level pate Rs l i ji i peraman 10 Disconnect the coaxial cable from the input connector Connect a dual input cable to the and input connectors then connect the coaxial cable from the Calibrator to the dual input cable 11 For AC coupled differential operation set the input to AC AC button in GND button out The calibrator signal is now coupled to both inputs as a common mode signal A straight line display should be observed since the common mode signal is being rejected Step Attenuator Balance Adjustment H this control is not properly adjusted the CRT zero reference point trace or spot will shift vertically due to differential DC imbalance in the amplifier as the VOLTS DIV switch
8. Tektronix 1071 Mi Number Serial Ine P O Box 500 Beaverton Oregon 97005 Phone 644 0161 6 Cables 070 1230 00 IX INSTRUCTION Tektron nn pie i a rene Kuren mn ds CONAN AOS ww ae se 22 A a ot SOROS EN SESS ESS SUA a aoe NAN Se SRG SAR DICKE EIERN EEE A MONNEREN ESS ANOS arr Ne d above should be taken up with your ER BR RAR BER Sa Ne ees fo SESE iS RES ESES SS RER RA ag ge EI TA ktronix Eie ineer or representa sce EIER RE ERS KS SENSE Reser ES EEE Sr Ayan DE WAY ARAN RR N SIRR ee A SNR RD CK Manca i WESEN ANA SEY RON AKRE Ae om ROO x VS ENESA RENANE a EINEN A Y SR KARAN ERS ARTEN to the Tektro RAYA DESK ROSES ERA ZO ZE l RARO tie ns Poet ER A SA A Aa er N ke eee TAS NOK E REN Cy at Satie a SR KK ESA NS 5 ne N NN y SRS ENS SAN OAA N a 5 y 58 mber with all requests for parts or A TE a e ate oe we r lt SEREN RR DESK kk en as RRO Rae DERW EE A OO ER talento ger EEE ew aia dae Wares e RER yet IE TSA A ER vr ER NN 3 EN AKRE ESA E OTRA E AA LISAS inlets PESAN EREN ee noe eee Ee NE EA eae kaz RR RANA PSE eier W AWAN ENA NA xa AA RAND HONS ane rivileges o lt tronix Inc Beaverton egon Printed in the United States of America EN x i i x ds Siena SEEN aero Ra EATERY
9. ame position AC or DC depending on the method of signal coupling required Only the voltage difference between two signals is in differential measurements frequency and phase are rejected See Fig 1 1 Operating Instructions 5A22N The ability of the 5A22N to reject common mode signals is indicated by the common mode rejection ratio CMRR CMRR is at least 100 000 1 at the input connectors for the lower deflection factors 10 uV DIV and 20 uV DIV when signals between DC and 30 kHz are DC coupled to the inputs To ilustrate this charac teristic assume that a single ended input signal consists of an unwanted 60 Hz signal at 1 volt peak to peak plus a desired signal at 1mV peak to peak If an attempt is made to display the described signal singie ended measurements at 2mV DIV the 60 Hz signal will produce a deflection equivalent to 5000 divisions and the 1 mV signal will be lost If the same 1mV signal is measured differentially with the 60 Hz signal common to both inputs no more than one part in 100 000 of the common mode signal will appear in the display The desired signal will produce a display of 5 divisions with not more than 0 1 division of display produced by the common mode signal CMRR not specified when residual display is 0 1 division or less There are a number of factors which can degrade common mode rejection The principal requirement for maximum rejection is for the common mode signal to arrive
10. as follows 1 Obtain a carton of corrugated cardboard having inside dimensions of no less than six inches more than the instrument dimensions this will allow for cushioning Refer to the following table for carton test strength requirements l 2 Surround the instrument with poiyethylene sheeting to protect the finish of the instrument 3 Cushion the instrument on ali sides by tight y packing dunnage or urethane foam between carton and instru ment allowing three inches on all sides 4 Seal carton with shipping tape or industrial stapler SHIPPING CARTON TEST STRENGTH Gross Weight Ib Carton Test Strength Ib 0 10 200 10 30 275 30 120 375 120 140 500 140 760 600 A A
11. asic functions of the 5A22N Operation of other instruments in the system is described in the instruction manuals for those units 1 Insert the unit ali the way into the oscilloscope system plug in compartment 2 Turn the oscilloscope intensity control fully counterciockwise and turn the oscilloscope system Power On Preset the time base and triggering controls for a 2 millisecond division sweep rate and automatic trig gering 3 Set the 5A22N front panel controls as follows 1 2 DISPLAY DISPLAY ON readout illuminates POSITION Midrange LF and HF 3 dB Full bandwidth VOLTS DIV AV STEP ATTEN BAL Midrange input Coupling DC GND Input Coupling DC GND NOTE About five minutes is sufficient time for warmup when using the 5A22N for short term DC measure ments For long term DC measurements using the lower deflection factors allow at least 15 minutes 4 Adjust the Intensity control for normal viewing of the trace The trace should appear near the graticule center 5 Move the trace two divisions below the graticule centerline with the POSITION control SOLON MA LO CAUTION LON LOL LO MO MM OE if the maximum input voltage rating at the gates of the input FET s is exceeded the gates are diode clamped at about or 12 0 volts If the signal source can supply more than 1 16 A the input protective fusefs will open 6 Apply a 400 millivolt peak to peak signal available at the oscilloscope
12. ation is comparison of signal amplitudes by ratio rather than by absolute voltage To accomplish this apply a reference signal to either input of the 5A22N and set the VOLTS DIV switch and Variable control so that the reference display covers the desired number of graticule divisions Do not change this setting of the Variable control throughout the sub sequent comparisons The settings of the VOLTS DIV switch can be changed however to accomodate large ratios In doing so regard the numbers which designate the switch positions as ratio factors rather than voltages Differential Operation Single ended measurements often yield unsatisfactory results because of interference resulting from ground loop currents between the 5A22N and the device under test In other cases it may be desirable to eliminate a DC voltage by means other than the use of a DC blocking capacitor which could Hmit the low frequency response These limitations of single ended measurements are effectively eliminated using differential measurements Differential measurements are made by connecting each input input and input to selected points in the test circuit Since the chassis of the 5A22N need not be connected in any way to the test circuit there are few limitations to the selection of these test points In any case do not exceed the maximum safe input voltages listed in Electrical Characteristics Both Input Coupling switches should be set to the s
13. d 1000X as well as other special purpose types are available through your Tektronix Field Engineer or Field Office Some measurement situations require a high resistance input to the 5A22N with very little source loading or signal attenuation In such situations a passive attenuator probe cannot be used However this problem may be solved by using an FET Probe or the high impedance input provision of the 5A22N High impedance Input In the 50mV through 10u4V positions of the VOLTS DIV switch where the input attenuator is not used the internal gate return resistors alone establish the 1 megohm input resistance The removal of the strap from the circuit board disconnects these resistors from ground and permits the input FET gates to float providing a very high input impedance The signal source must then provide a DC path for the FET gate current The input signal must be kept to relatively low amplitudes since the deflection factor is restricted to 50 mV Div through 10 uV div and DC coupling must be used The DC plus AC voltages on the test points with respect to the chassis potential of the 5A22N should be limited to the leveis fisted in Etectrical Characteristics under Common Mode Rejection Higher levels will degrade the common mode rejection ratio and exceed the input voltage rating of the unit 1 4 NOTE In the 0 1 V to 5V range of the VOLTS DIV switch the input impedance is paralleled by the resistors in the
14. is rotated throughout its range The shift is more noticeable on the most sensitive positions a With the instrument operating ground both the and inputs GND buttons pushed in set the VOLTS DIV switch to 5V and move the trace to graticule center with the POSITION control b Adjust the STEP ATTEN BAL control for minimum trace shift as the VOLTS DIV switch is rotated throughout Its range Gain Check Whenever the 5A22N is inserted into a plug in com partment other than the one in which it was calibrated the amplifier gain may be checked and if necessary adjusted See the Calibration Procedure in this manual for complete instructions GENERAL INFORMATION Applying Signals CAUTION Discs bie eens If the 5A22N input is connected to a large DC voltage source without using the pre charge pro vision the peak charging current into a OT uF capacitor will be limited only by the internal resistance of the signal source and this source may be damaged When measuring DC voltages use the largest deflec tion factor 5 V Div when first connecting the 5422N Operating Instructions 5A22N to an unknown voltage source If the deflection is too small to make the measurement switch to a lower deflection factor If the input stage is overdriven a large amount of current might flow into the input and open the protective fuse See CAUTION after item 5 of the Basic Operation Pre charging When only the AC compo
15. nent of a signal having both AC and DC components is to be measured use the input Coupling switches AC and GND pushbuttons to take advantage of the pre charging circuit incorporated in the unit The pre charging circuit permits charging the coupling capacitor to the DC source voltage when the AC and GND buttons are pressed in The procedure for using this circuit is as follows a Before connecting the 5A22N to a signal con taining a DC component push in the AC and GND buttons Then connect the input to the circuit under test b Wait about one second for the coupling capacitor to charge c Remove the ground from the coupling capacitor GND button out The display will remain on screen and the AC component can be measured in the usual manner The above procedure should be followed whenever a signal having a different DC level is connected Signal Input Connectors When connecting signals to the and input con nectors on the 5A22N consider the method of coupling that will be used Sometimes unshielded test leads can be used to connect the 5A22N to a signal source particularly when a high level low frequency signal is monitored at a low impedance point However when any of these factors is missing it becomes increasingly important to use shielded signal cabies In all cases the signal transporting leads should be kept as short as practical When making single ended input measurements con ventional amplifier ope
16. of external voltage signals Con nector labeled indicates that a positive going signal will cause up ward deflection connector labeled indicates that a positive going and Input BNC connectors for Connectors cause downward deflection Connectors include coded probe input rings for acti vation of X10 readout signal will BASIC OPERATION Preparation The 5A22N is calibrated and ready for use as it is received It can be installed in any compartment of the 5100N Series Power Supply Amplifier module but it is intended for primary use in vertical compartments the center and left compartments For X Y operation the 5A22N may also be installed in the horizontal right compartment refer to the Oscilloscope System instruction manual for information on X Y operation NOTE The Power Supply Amplifier module is designed so that in the absence of DISPLAY logic levels from the vertical plug ins it will display the out put of the unit in the left compartment To install align the upper and lower rails of the 5A22N with the plug in compartment tracks and fully insert it the plug in panel must be flush with the oscilloscope panel To remove pull the release latch to disengage the 5A22N from the oscilloscope The first few steps of the following procedure are intended to help place the trace on the screen quickly and prepare the instrument for immediate use The re mainder of the steps demonstrate some of the b
17. ration be sure to establish a common ground connection between the device under test and the 5A22N The shield of a coaxial cable is normally used for this purpose 1 3 Operating Instructions 5A22N In some cases differential measurements require no common ground connection and therefore are less susceptible to interference by ground oop currents Some problems with stray magnetic coupling into the signal transporting leads can also be minimized by using a differential rather than a single ended measurement These considerations are discussed later in this section under Differential Operation it is always important to consider the signal source loading and resulting change in the source operating characteristics due to the signal transporting leads and the input circuit of the 5A22N The circuit at the input connectors can normally be represented by a 1 megohm resistance to ground paraileled by the 47 pF A few feet of shielded cable 20 to 40 pF per foot may increase the parallel capacitance to 100 pF or more In many cases the effects of these resistive and capacitive loads may be too great and it may be desirable to minimize them through the use of an attenuator probe Attenuator probes not only decrease the resistive capacitive loading of a signal source but also extend the measurement range of the 5A22N to include substan tially higher voltages Passive attenuator probes having attenuation factors of 10X 100X an
18. th frequency is limited to 2 hertz by the coupling capacitor This control also provides DC off set operation when in the DC OFFSET position LF 3 dB VOLTS DIV Variable Volts Div DC OFFSET STEP ATTEN DCBAL Input Coupling Pushbutton Input Coupling cont Pushbutton 5A22N Volts per major graticule division Selects calibrated deflection factor in a 1 2 5 sequence from 10 uV Div to 5 V Div in 18 steps Knob skirt is illuminated to indicate deflection factor and X10 scaling of readout is provided automatically when a 10X coded probe is used Provides uncalibrated contin uously variable deflection factor between calibrated steps extends range to 12 5 V Div COARSE and FINE controls provide on screen display of small signal variations on relatively large DC levels LF 3 dB switch must be in the DC OFFSET position Balances the input amplifier for minimum trace shift throughout the deflection factor gain switching range AC DC Button pushed in selects capacitive coupling of signal applied to associated input con nector button out selects direct coupling of input signal GND Disconnects the input signal and provides ground ref erence to the amplifier input stage PRE CHG Both AC DC and GND buttons pushed in permits precharging of the coupling capa citor to the input signal DC level Release GND button for measure ment 1 1 Operating instructions 5A22N application
19. tion is 1 megohm for 10X 10 megohms Probe compensation is obtained in the usual manner see probe manual for details ELECTRICAL CHARACTERISTICS in this manual the word Volts Div or division refers to major graticule division Performance Conditions The following characteristics apply when the 5A22N is operating within the environment described in the 5100 Series Oscilloscope System manual In addition the 5A22N must have been calibrated at an ambient temperature between 20 C and 30 C Bandwidth 3 dB DC DIRECT COUPLED DC to at least 1 MHz independent of deflection factor Selectable high and low frequency limits AC CAPACITIVE COUPLED 2 Hz to at least 1 MHz High and Low 3 dB Frequencies HF 3dB Selectable from 0 1 kHz to 1 MHz in a 7 step 1 3 10 sequence i Operating Instructions 5A22N LF 3 dB Selectable from DC to 10 kHz in a 7 step 14 10 100 sequence Limited to 2 Hz when AC coupled Deflection Factor 10 gV div to 5 V div within 2 in an 18 step 1 2 5 sequence Uncalibrated continuously variable between steps and to 12 5 V div Common Mode Rejection DC DIRECT COUPLED At least 100dB DC to 30 kHz at 10 uV div to 0 1 mV div with up to 20 V P P sine wave decreasing by 20 dB decade or less on lower deflection factors up to 50mV div At least 50 dB 0 1 V div to 5 V div with up to 100 V P P sine wave At least 50 dB at any deflection factor with two P6060 probes
20. trace pulses on the displayed Rewan 1 i i i H H ua s ve d The above procedure matehes the probes for use at any sensitivity which employs the particular 5A22N input attenuator 1X or 100X used in steps b and c lt When it is necessary to use the other input attenuator steps b and c should be repeated for that attenuator e When examining a small differential signal in the presence of relatively large common mode components fine adjustment of probe CMRR may be made by temporarily connecting both probes to either of the two signal sources f Movement of the probes should be kept to a minimum after the adjustment Coded Probes The 5A22N is designed for compatibility with coded probes such as the Tektronix P6060 or P6052 1X 10X Passive Probe The and input connectors have an outer ring to which the coding ring on the probe connector makes contact This type of probe allows the vertical deflection factor indicated by the readout to correspond with the actual voltage at the probe tip eliminating the need to consider the attenuation factor when measuring the signal amplitude on the graticule scale Attenuation on the P6052 probe is selected by a sliding collar on the probe barrel When the collar is pulled back away from the probe tip 1X attenuation is selected when the collar is pushed forward nearest the probe tip 10X attenuation is selected Input resistance for 1X attenua
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