Hewlett Packard 209A Sine/Square Oscillator
Contents
1. OPERATING AND SERVICE MANUAL hp Part No 00209 90002 MODEL 209A SINE SQUARE OSCILLATOR Serials Prefixed 818 0 5 Section I Model 209A Table 1 1 Specifications RANGES Frequency 4 Hz to 2 MHz in 6 ranges PERFORMANCE RATINGS Dial Accuracy 3 of frequency setting Flatness At maximum output into 600 ohm load 1 kHz reference LOW Distortion 1 40 5 1 5 Mode Normal Mode Hz Distortion DISTORTION dB x 1 0 Q 8 k go Q FREQUENCY Hz Hum and Noise less than 0 01 of output OUTPUT CHARACTERISTICS SINE WAVE Output Voltage 5 V rms 40 mW into 600 ohms 10 V open circuit Output can be floated up to t 500 V peak between output and chassis ground Output Impedance 600 ohms Output Control 20 dB range continuously adjustable Output Balance greater than 40 dB below 20 kHz 1 0 SQUARE WAVE Output Voltage 20 V p p open circuit symmetrical about 0 V Output can be floated up to 500 V peak between output and chassis ground Rise and Fall Time less than 50 ns Symmetry 5 Output Impedance 600 to 900 ohms depending upon setting of output control EXTERNAL SYNCHRONIZATION Sync Impedance 10 kilohm Sync Output Sine wave in phase with output amplitude working into 1 megohm shunted by 100 pF is greater than 1 7 V rms from 4 Hz to 50 kHz greater than 1 V from 50 kHz to 2 MHz Sync Input Oscillator2. the output voltage and is controlled by A2Q3 A2Q2 is a current source for A2Q3 Zener diode A2CR5 furnishes bias for A2Q2 while A2R2 injects negative ripple feedback A2CR6 sets the emitter voltage of A2Q3 setting up a reference for the supply output current limits the output to prevent damage to the supply
3. N ON PROCEDURE 34 To turn on the Model 209A proceed as follows a Set the two position voltage selector switch on the rear panel to the value of available line voltage b Connect the AC power cord to line voltage c Switch the RANGE switch from OFF to the desired frequency range d Select the desired frequency and voltage output with the frequency dial and amplitude controls respectively 3 5 OPERATING CONSIDERATIONS 3 6 FLOATING OUTPUT WHEN THE GROUND STRAP ON THE REAR PANEL IS CONNECTED INPUT GROUND IS AT EARTH GROUND POTENTIAL 3 7 When the ground strap on the rear of the Model 209A is disconnected the chassis is isolated from power ground The outputs may then be connected to any point with a dc potential of not more than 500 volts If a dc voltage up to 500 volts is connected between the ground connectors on the rear panels the oscillator output is dc offset by that amount INSTRUCTIONS 3 8 BALANCE 3 9 With the chassis isolated from the cabinet the sine wave output will be balanced to greater than 40 dB at frequencies below 20 kHz If the square wave output is being used simultaneously with the black terminal connected to ground the sine wave output will no longer be balanced 3 10 SYNCHRONIZATION 3 1 1 The Model 209A is equipped with a SYNC terminal that provides a sync output signal or accepts a synchronizing input signal from an external source The sync output signal is a 1 7 v
4. TION IV THEORY OF OPERATION 4 1 INTRODUCTION 4 2 This section contains a description of the basic principles of circuit operation for the Model 209A The information is presented as a discussion of each block indicated on the Block Diagram Figure 4 1 and detailed circuit descriptions which refer to Figure 7 1 and 7 2 4 3 The Model 209A is basically a Wien bridge oscillator The output from the oscillator circuit is applied to a buffer amplifier and to a sine wave to square wave converter These two circuits provide independent sine wave and square wave outputs respectively 4 4 BLOCK DIAGRAM DESCRIPTION 4 5 BRIDGE AND AMPLIFIER 4 6 An overall loop gain of at least unity is a requirement for any amplifier to oscillate The Model 209A satisfies this requirement with a combination of positive and negative feedback through the bridge FREQUENCY Q te w 5 5 RATIO 3 POSITIVE FEEDBACK VOLTAGE TO AMPLIFIER Eo a OSCILLATOR CIRCUIT OUTPUT VOLTAGE Fo FREQUENCY WHERE af sT0 8 1700 Figure 4 2 RC Frequency Network Characteristics 4 7 The oscillator bridge is divided into two networks the frequency selective network and the negative feedback network Positive feedback is furnished through the frequency determining network of CIA R8 CIB and R16 At the frequency that the phase of the positive feedback is X R and the maximum ratio of output voltage is supplied
5. can be synchronized to external signal For 5 V rms input sync frequency can be as much as t 7 away from set frequency sync range Sync range is a linear function of sync voltage GENERAL Operating Temperature Instrument will operate within specifications from 0 C to 55 C Storage Temperature 4 C to 75 C Power AC Line 115V or 230V 10 48 Hz to 440 Hz less than 7 W Dimensions Refer to Figure 2 1 page 2 2 Accessories Available HP 11075A Instrument Case Model 209A Section I SECTION GENERAL l I INTRODUCTION 1 2 This section contains general information about the hp Model 209A Sine Square Oscillator Throughout this manual the instrument will be referred to as the Model 209A 1 3 SPECIFICATIONS 14 Table 1 1 lists the specifications for the Model 209A 1 5 DESCRIPTION 1 6 The Model 209A is a versatile signal source with independent sine wave and square wave outputs at frequencies from 4 Hz to 2 MHz The square wave amplitude is variable to a maximum of 20 volts peak to peak into open circuit The sine wave amplitude is variable to a maximum of 10 volts rms into open circuit from a constant 600 ohm source When working into a 600 ohm load the maximum output level is 5 volts rms 1 7 Balanced output can be obtained by disconnecting the grounding strap at the rear of the instrument This isolates the chassis from the cabinet and line ground The sine wave ou
6. he peak comparator The oscillator amplifier output is held to 7 2 volts peak amplitude 4 12 When the oscillator is first turned on the AGC gives the amplifier a gain of much greater than three Noise in the amplifier is amplified greatly and the frequency selective network in the Wien bridge selects the noise at the tuned frequency The selected noise becomes positive feedback to the amplifier and the amplifier starts oscillating at the tuned frequency As the output amplitude approaches 7 2 volts peak the 4 1 Section IV AGC reduces the gain of the amplifier to three and stable oscillation is achieved 4 13 BUFFER AMPLIFIER 4 14 The 5 volt rms sine wave output from the oscillator circuit is coupled to the buffer amplifier The amplifier has a high open loop gain that is controlled by the negative feedback to provide a gain of 2 This enables the circuit to have very low distortion characteristics The buffer amplifier uses a complementary symmetry transistor pair to furnish a 10 volt rms output 4 15 SINE SQUARE CONVERTER 4 16 The 5 volt rms sine wave output from the oscillator circuit is also applied to the sine square converter The sine wave is coupled to a tunnel diode which produces a small square wave output with fast rise and fall times This small square wave signal is then shaped and amplified It appears at the output as a 20 volt peak to peak square wave 4 17 DETAILED CIRCUIT DESCRIPTION 4 18 Fo
7. ithin desired range Dial setting multiplied by RANGE switch position indicates output frequency Frequency Vernier Provides fine tuning of frequency dial 4 Square Wave Amplitude Control Varies Square Wave output level to 20 volts peak to peak open circuit Sine Wave Amplitude Control Varies Sine Wave output level over a 20 dB range to 10 volts rms open circuit 5 volts rms into 600 ohms Sine Wave Output Terminal 600 ohm sine wave output at a frequency and amplitude determined by control settings 118 230V 10 48 440 TVA MAX d Square Wave Output Terminal 600 ohm square wave output at a frequency and amplitude determined by control settings SYNC Terminal 1 Input terminal for an external sync signal 2 Output terminal for 1 7 volt rms sine wave sync signal Ground Strap Connects the floating circuit ground to power ground 8 Voltage Selector Switch Selects line voltage of 115 volts or 230 volts AC i AC Power Receptacle Mates with power cord supplied with this instrument for line voltage connection NORM LOW DIST Switch Selects normal or low distortion below 100 Hz Figure 3 1 Description of Controls and Connectors Model 209A Section III SECTION Ill OPERATING 3 1 INTRODUCTION 3 2 This section contains information as an aid to operating the Model 209A Included are control and connector descriptions Figure 3 1 and some special operating considerations 3 3 TUR
8. o reduce the output amplitude of the amplifier 4 23 Transistors Al Q13 through Al Q18 comprise a buffer amplifier with a gain of two AIQI3 and Al Q14 form a differential amplifier Diodes AICR18 and AICR19 furnish proper biasing for complementary output transistors Al 017 and When the output attenuator AIR79 is fully clockwise the output amplitude is greater than 10 volts rms When the attenuator is fully counter clockwise the output is attenuated by greater than 20 dB 4 24 The Sine Square Converter circuit includes through 2 This converter circuit operates as a saturating amplifier Tunnel diode AICR12 squares the sine wave input and the Symmetry Adjust AIR45 determine the level where conduction starts This provides for adjustment of the symmetry of the square wave Zener diode AICRIS sets the voltage level of the negative portion of the square wave Al Q12 furnishes the positive portion of the square wave output and AlOll furnishes the negative output 4 25 POWER SUPPLY 4 26 The following paragraphs refer to the Power Supply Schematic Figure 7 2 4 27 This power supply is a series regulated power supply furnishing 21 volts and 21 volts Zener diode A2CR6 serves as a reference for the positive power supply which in turn serves as the reference for the negative supply The positive supply is described here and the negative supply operates similarly 4 28 Transistor A2QI regulates
9. olt rms sine wave in phase with the oscillator output The external sync signal can be any periodic waveform of sufficient amplitude to maintain sync For an external sync signal with an amplitude of 5 volts rms the oscillator will remain synchronized at frequencies of 7 of the set frequency 3 12 The Model 209A can be synchronized to any significant harmonic of an external signal However if a harmonic or non sinusoidal waveform is used to synchronize the Model 209A some portion of the external sync signal will be on the output This small signal will appear as distortion The amount of this apparent distortion will be directly proportional to the amplitude of the sync signal For a non sinusoidal sync input of 2 volts peak to peak the distortion will be down about 45 dB for frequencies which are normally down 60 dB 3 13 LOW DISTORTION 3 14 At frequencies below 100 Hz distortion can be reduced by switching the NORM LOW DIST switch on the rear panel to LOW DIST In the LOW DIST mode the Model 209A will have a longer settling time when changing frequencies To avoid this set the desired frequency before switching to LOW DIST 3 1 FREQUENCY DIAL 209 8 614 N E S akan N BRIDGE Figure 4 1 AJ BUFFER Las AMPLIFIER PEAK COMPARATOR SYNC 7 2 REF 5 l 2 Model 209A Block Diagram gt 5 Model 209A Section IV SEC
10. r the following paragraphs refer to the Oscillator Schematic Diagram Figure 7 1 4 19 Transistors AlQI through AIQ7 make up the basic oscillator amplifier 5 an N channel FET AICRI sets up proper dc bias for AlQ2 Diodes AICR6 AICR7 AICR8 set up proper bias for AlQ4 Capacitor AIC9 is chosen to provide a stable roll off at high frequencies AlQ7 is a current source for AIQ3 and AlQ4 AICR4 and AICRS provide proper biasing for complementary output transistors 5 and 4 20 The positive feedback arm of the Wien bridge consists of tuning capacitors AlClAand AICIB and range switching resistors Al through Al R17 4 21 The negative feedback arm of the Wien bridge depends upon the ratio of the impedance of AIR28 to the total impedance of AIR23 AIR24 AIR25 and AIR25 reduces the effect of the FET to increase stability AIQ8 provides AGC for this amplifier by varying impedance to obtain the proper negative feedback 4 2 Model 209A 4 22 The conduction of FET AlQ 8 is controlled by the peak detector circuit using Al Q9 Al Q9 conducts during the most negative portion of each negative half cycle developing a negative charge in AIC15 and its parallel capacitors As the amplifier output amplitude increases conducts more and AIC15 becomes more negatively charged This makes the FET input voltage more negative increasing its impedance and increasing the negative feedback t
11. to the amplifier see Figure 4 2 The characteristics of the Wien bridge are such that the output voltage to the input of the amplifier at F is one third the amplitude of the positive feedback voltage Therefore to maintain unity gain and oscillation the negative feedback network R28 R24 and AGC was designed with a divider ratio of two to one to give the amplifier a gain of three 4 8 The amplifier itself is a solid state high gain amplifier with the output in phase with the input so that feedback will produce oscillations 4 9 PEAK COMPARATOR AND AGC 4 10 The voltage output from the Wien bridge to the input of the amplifier is not always one third of the positive feedback voltage at all operating frequencies nor is the amplifier gain constant for all operating frequencies One technique used for maintaining unity gain in the oscillator circuit at all operating frequencies is to have a dynamic resistance variable with changes in gain in the negative feedback network In the Model 209A this is accomplished with the combination of the peak comparator and AGC circuits 4 11 The peak comparator compares the negative peak of the oscillator amplifier output to a 7 2 volt reference If the output varies above or below the reference voltage a difference voltage will be supplied to the AGC circuit The dynamic resistance of the AGC circuit is a field effect transistor with the gate controlled by the difference signal from t
12. tput will balance to ZORA OSCILLATOR vy MW f INFORMATION greater than 40 dB at frequencies below 20 kHz with the chassis isolated 1 8 The Model 209A can be synchronized with an external source With a 5 volt rms sync input the external source may vary as much as 7 in frequency and the Model 209A will remain synchronized 1 9 A sync output of 1 7 volts rms is also available at the same front panel terminal used to accept an external sync source I 10 INSTRUMENT MANUAL IDENTIFICATION 1 1 1 Hewlett Packard uses a two section serial number The first section prefix identities a series of instruments The last section suffix identifies a particular instrument within the series If a letter is included with the serial number it identifies the country in which the instrument was manufactured If the serial prefix of your instrument differs from the one on the title page of this manual a change sheet will be supplied to make this manual compatable with newer instruments or the backdating information in Appendix C will adapt this manual to earlier instruments All correspondence with Hewlett Packard should include the complete serial number La 5 Otay PACKARD K WL lijs 3 6 Figure l 1 Model 209A Sine Square Oscillator 1 1 Section II Model 209A HEWLETT PACKARD RANGE Switch Selects frequency range or OFF position Frequency Dial Selects frequency w
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