electronic signal generators · 2013-08-31 · electronic signal generators a range of pulses from...

'•i NASA SP-5946(01)

TECHNOLOGY UtlLlMtlON

ik, CORY,

ELECTRONIC SIGNAL GENERATORS

A COMPILATION

NATIONAL AERON A UTICS AND SPACE ADMINISTRATION

https://ntrs.nasa.gov/search.jsp?R=19720004434 2020-04-30T09:23:37+00:00Z

ForewordThe National Aeronautics and Space Administration and the Atomic Energy

Commission have established a Technology Utilization Program for the dissemina-'tion of information on technological developments which have potential utility'outside the aerospace and nuclear communities. By encouraging multiple applica-tion of the results of their research and development, NASA and AEC earn forthe public an increased return on the investment in aerospace research and devel-opment programs.

The innovations in this compilation deal with electronic circuits and repre-sent a carefully selected collection of items on electronic signal generators. ,Most of the items are based on well-known solid-state concepts that have beensimplified or refined to meet NASA's demanding requirements for reliability,simplicity, fail-safe characteristics, and the capability of withstanding environ-mental extremes. The items included in the sections dealing with pulse gener-ators and oscillators should be of particular interest to the electronic hobbyist,because of their simplicity and low cost.

Additional technical information on individual devices and techniques can berequested by circling the appropriate number on the Reader Service Card in-cluded in this compilation.

Unless otherwise stated, NASA and AEC contemplate no patent action onthe technology described.

We appreciate comment by readers and welcome hearing about the relevanceand uti l i ty of the information in this compilation.

Ronald J. Philips, DirectorTechnology Utilization OfficeNational Aeronautics and Space Administration

NOTICE • This document was prepared under the sponsorship of the Nat ional Aeronautics and SpaceAdministration. Neither the United States Government nor any person acting on behalf of the UnitedSlates Government assumes any l iabi l i ty resulting from the use of the information contained in thisdocument, or warrants that such use will be free from privately owned rights.

For sale by the National Technical Information Service, Springfield, Virginia 22151. $1.00

Table of ContentsSECTION! . Pulse Generators Page

Monostable Mult ivibrator Has High StabilityOver Wide Temperature Range 1

Resettable Monostable Pulse Generator 1Nanosecond Pulse Generator 2Wide Frequency Range Pulse Generator 3

' A Variable Pulse Generator . 4

SECTION 2. High Voltage Pulse GeneratorsHigh-Power Monostable Pulse Generator Controls

Solenoid Valve Operation 4, Solid-State High Voltage Pulse Generator 5

High-Current Pulse Generator 6Pulse Generator Delivers High-Speed Pulses

' at Megawatt Levels 6A Simple, High Voltage Pulse Generator

for Wide-Gap Spark Chambers 7High Voltage Pulse Generator Produces Fixed

Energy Pulse 8

SECTION 3. OscillatorsLow Power, Compact, Voltage-Controlled Oscillator 9Voltage-Controlled Oscillator 10Constant-Amplitude RC Oscillator 11A 225 MHz FM Oscillator with Response to 10 MHz 12Oscillator Uses Transistor as Inductive Element 12Automatic Frequency Control of Voltage-Controlled

Oscillators 13

SECTION 4. Analog Signal GeneratorsCircuit Generates Complex Waveforms 14Sine Function Generator 14Circle-Notch Generator Circuit 15 .Digital-Voltage Curve Generator 16

SECTION 5. Square Wave Signal GeneratorsVariable Pulse Generator Switch 17Square Wave Generator for High Frequency

Applications 17Square Wave Generator Has'Variable Duty Cycle 18Single Transistor Circuit Boosts Pulse Amplitude 19

SECTION 6. Special Function Signal Generators400 Hz Noise Generator 19Constant Frequency, Voltage-to-Duty-Cycle Generator 20Linear DC Analog Voltage-to-Pulse Width Converter 21Constant-Frequency, Variable Duty Cycle

Multivibrator 22Ultrastable Reference Pulse Generator

for High-Resolution Spectrometers 22

Section!. Pulse Generators

MONOSTABLE MULTIVIBRATOR HAS HIGH STABILITYOVER WIDE TEMPERATURE RANGE

A differential comparator is used to generatehighly stable pulses over wide variations in tem-perature and supply voltage. Ql and Q2 (see fig.)

operate as the differential comparator, with thesupply voltage switched by Q4. In the quiescentstate, Q3 and Q4 are cut off, thereby limitingpower dissipation to the transistor leakage cur-rents. Triggering is accomplished by applying a

short durat ion, positive pulse at point A. The trig-ger pulse tu rns on Q3 which then tu rns on Q4. Thebase current of Q3 flowing through Q4, R3, D2,and Dl keeps Q3 conducting.

When Q4 is conducting, point D is held at avoltage close to the voltage of point C. Untilcapacitor Cl is charged to approximately thevoltage at point C, Q2 is cut off. Once Q2 startsto conduct, the voltage at E drops sufficiently toremove Q3 from a saturation condition. When Q3is no longer saturated, Q4 is cut off, and theentire circuit once again assumes the quiescentstate.

Ql and Q2 are closely matched transistors (ide-ally, a matched monolithic pair) to assure nearlyidentical base-emitter voltages over the usabletemperature range. The circuit is capable ofgenerating a pulse with periods varying fromS^sec to 100 msec over a 223 K to 373 K tem-perature range.Source: W. C. Roehr, Jr., and R. C. Grimmer of

IBM Electronics Systems Centerunder contract to

Goddard Space Flight Center(GSC-10657)

No further documentation is a vailable.

RESETTABLE MONOSTABLE PULSE GENERATOR

A new pulse generator is capable of producingan output pulse which begins upon receipt of arandom input signal. The termination time of theoutput pulse can be preset to a specified pulsewidth from the beginning of the input pulse. Thecircuit continues to generate the specific outputpulse width as long as a reset pulse occurs to re-cycle the pulse generator during a predetermined

time period. If no input pulse occurs during thepredetermined time period, the output pulse re-turns to a quiescent state. The pulse generator isparticularly suitable for use where small packingvolume, low power consumption, and simplicityare needed.

The resettable monostable pulse generator (seefig.) includes a charge run-down timing circuit

1

BLKCTRONIC SIGNAL GhNbRATORS

with a capacitor that is charged to a peak value bya random pulse from a constant amplitude pulsesource. After being charged, C2 immediately startsto discharge through Q3 and Q4. The primary dis-charge path is through Q4, with Q3 drawing

is

n 01

I>

02

Q5(TQ3_ VkfS^ . . K

InputPulse

-VA

capacitor is again charged to its peak value. Thisreset pulse prevents terminating the output pulseand recycles the termination time of the outputpulse (pulse width) to be measured from the in-ception of the last reset pulse. Each time a reset

Output

-A/W

Charge Run-down Timing Section

Pulse Generator

enough current to maintain it in the "on" condi-tion. Q3 turns Q2 on, and the emitter signal of Q2is applied through Rl to the output pulse genera-tor. The output pulse generator starts to generatea pulse as soon as C2 is charged to its peak value,and continues to generate the output pulse untilthe charge drops to a predetermined level. If asecond pulse from the constant amplitude pulsesource occurs during this run-down period, the

pulse occurs during a run-down period, the capac-itor is recharged to its peak value; hence, the out-put pulse exists for a time period depending onthe occurrence of the random reset pulses.

Source: N.M.GarrahanGoddard Space Flight Center

(XGS-11139)

Circle I on Reader Service Card.

NANOSECOND PULSE GENERATOR

Short duration, fast rise-time pulses with zero dccomponents are generated by a new coaxial linepulser. The output pulses can be directly radiatedby a broadband antenna instead of being used tomodulate a carrier frequency.

When the 300 Vdc supply is applied to the coax-ial cable, the capacitance of the cable begins tocharge through Rl (see fig.). The voltage on thecenter conductor of the cable also appears on thecollectors of Ql and Q2. Ql is chosen to have alo'wer avalanche threshold than Q2. Therefore,as the voltage on the cable increases, Ql firesand enters a low impedance conducting state. This

connects end A of the coaxial cable to the loadRL. The sharp increase of voltage across RL iscoupled through capacitor Cc to the collector ofQ2, causing Q2 to fire also. The firing of Q2 shortcircuits end B of the coaxial cable.

In the charged condition, the cable generatestwo equal amplitude waves which travel in oppo-site directions and are reflected at the cable ends.When Ql fires, the wave traveling in the directionfrom B to A is coupled into the matched load RLand there is no further reflection at A. At B, how-ever, the wave traveling from A to B is reflectedwith a polarity inversion because of the short cir-

PULSE GENERATORS

cuit produced by Q2. The voltage across RL isthe voltage at end A of the cable. When the tran-sistors fire, the voltage across RL rises from zeroto one-half of the initial voltage on the cable.

Coaxial Cable +300Vdc<

but less than the avalanche threshold of Ql orQ2,the cable will become charged and no further ac-tion will occur. Avalanche may then be initiatedby applying a trigger pulse to the collector of Ql.

R1• 1 Trigger Input

-II—0

01

t®•A/W

RL

Vo

;cc30 nsec

After the transistors have fired, the voltageacross RL undergoes an abrupt polarity reversal.After a short period of time, the cable is dis-charged, the transistors turn off, and the chargingcycle begins again. If the input voltage is large

Source: R. A. CliffGoddard Space Flight Center

(GSC-10516)

No further documentation is available.

WIDE FREQUENCY RANGE PULSE GENERATOR

9+5VDual Potentiometer

Multivibrator

10 to 100kHz

T "6100kHz

Lr

/

610kHz

^

v

1 kHz 100Hz

Zl

A10Hz 1Hz


A range of pulses from one pulse every 10seconds :to 20,000 pulses per second is availablewith this well-designed pulse generator (see fig.).The pulse generator uses a circuit consisting of twoone-shot multivibrators. The period of each multi-vibrator is^ linearly controlled over a frequencyrange of 10 kHz to 100 kHz by a ganged potenti-ometer. The output of the multivibrator is fed intoa series of 5 decade counters which produce outputpulses as low as one per second. The circuit has

been designed with integrated circuit transistorlogic using a 5 V power supply. Frequency stabil-ity is very good, and the frequency versus controlresistance is linear.

Source: H.H.HoltofSperry Rand

under contract toMarshall Space Flight Center

(MFS-21197)


A VARIABLE PULSE GENERATOR

The variable pulse generator circuit (see fig.)produces a continuous train of pulses whose rep-etition rate and width are adjustable. The circuit

+ Vr

SSffi1

consists of a relaxation oscillator and the pulseshaping components. Potentiometer R 1 varies therepetition rate by varying the charge time ofcapacitor Cl. This controls the time between suc-cessive fir ings of the unijunction transistor Ql.Potentiometer R2 adjusts the pulse width by con-trolling the charge time of capacitor C2. The varia-tion in charge time determines the time periodover which the base of Q2 is provided with suf-ficient current for saturation. The pulse width canbe adjusted from one to several hundred micro-seconds.

Source: A.T. Nasuta, Jr. ofWestinghouse Electric Corp.

under contract toGoddard Space Flight Center

(GSC-90506)

•=• No further documentation is available.

Section 2. High Voltage PulseGenerators

HIGH-POWER MONOSTABLE PULSE GENERATOR CONTROLSSOLENOID VALVE OPERATION

This circuit (see fig.) consists of a dc semicon-ductor switch and a timing circuit which gate a100 msec burst of power (48 W) to a solenoid

valve. It is particularly useful for controlling largeamounts of power in applications requiring long

life, low maintenance, high reliability, low stand-by-power dissipation, small space, and rapid re-setting.

When the circuit is stabilized, Q3 is conductingand Q2 is turned off. When Q2 is triggered, it fires

PULSE GENERATORS

cc

TriggerInput

SiliconControlledRectifier

and causes power to be applied to the load RL.The negative load pulse is commutated throughCl to cut off Q3. Q3 is triggered "on" after atime-delay determined by the constant currentsource (R4, R5, R6, and Q 1) which charges C2 tothe zener breakdown voltage of D2. When D2breaks down, current from Ql flows into the gateof Q3. D 1 is used when the load is inductive.

Source: J.D'ArcyofRadio Corp. of America


(GSC-90300)


SOLID-STATE HIGH VOLTAGE PULSE GENERATOR

A solid-state pulse generator delivers a 20 kVpulse to a 100 pF load with a rise and fall time ofless than 1 Msec and a pulse width between 10 and100 Msec.

A positive input pulse of 2 or 3 V switches Qlon (see fig.). When Ql begins to conduct, the col-lector voltage decreases, turning on Q2. The sameoperation occurs when the collector of Q2 de-creases, switching on Q3, with base current flow-ing through R2. The switching times of Q2 and Q3are limited only by the response of Ql, Q2, andQ3, since they are switched with emitter drivevoltage. Therefore, the switching speed of thecomplete circuit is limited almost entirely by theswitching of Ql. The transistor string is protectedfrom spurious high voltage spikes by high voltagerectifier diodes Dl and D2. The rise and falltimes of the pulse can be decreased by usinghigher frequency transistors. The important fea-tures of the pulse generator are the availabilityof a positive or negative pulse at the output, with-out t ransformer coupling, and the protection ofthe circuit components against high voltage break-down with the use of the diode biasing scheme.

+ 1000V.

out

C2

' in o

Source: D. O. Hansen ofTRW Space Technology Laboratories

under contract toNASA Headquarters

(HQN-10050)

Circle 2 on Reader Service Card.


HIGH-CURRENT PULSE GENERATOR

A high-current pulse generator (see fig.) con-tains a storage capacitor which discharges into theload through input transistor Ql, the first siliconcontrolled rectifier SCR1, and resistors Rl and

undergoes negligible discharge, permitting anaverage current-to-peak-current ratio that ap-proaches the duty' cycle ratio. In this manner,high-current pulses can be generated with high

Start PulseTerminal

Stop Pulse'Terminal

R2. Upon application of a pulse to the stop pulseterminal , SCR2 is turned on, divert ing the loadcurrent through it and t u r n i n g on Q2. Shortlyafter , SCR1 and SCR2 are turned off, andf ina l ly Q2 is turned off. The cycle is repeated uponapplication of the next start pulse.

The pulse on-time and the circuit storage timerepresent a small fraction of the interpulse period.The storage capacitor, under these conditions,

circuit eff iciency^ The pulse on-time is determinedby the turn-on characteristics of the circuitelements.

Source: M. G. Woolfson ofWestinghouse Electric Corp.

under contract toManned Spacecraft Center

(MSC-405)


PULSE GENERATOR DELIVERS HIGH-SPEED PULSESAT MEGAWATT LEVELS

This solid state, high-speed circuit has been de-signed for application as a klystron cathodepulser. The circuit delivers 3 kW, 3 kV pulsesfrom a b i f i l a r f i lament transformer. Unl ike most

.state-of-the art pulsers, which require high supply

voltages to generate high-voltage pulses, only 65Vare required to generate a 3 kV pulse. The circui t(see f ig.) offers advantages in operational safetyand reliability and in improved packaging. Thespecial components which make low-voltage op-

PULSE GENERATORS

eration possible are broadband video transformerswound in mul t i f i la r toroids and loop-couplingtoroids.

safe, secondary breakdown region. Coupling andmatching from the drive amplifier to the dual baseinput circuit of transistors Q3 and Q4 are made

+ 65V

Transistors Ql and Q2 form a stabilized ampli-fier with a 15 dB power gain. Stabilization isachieved by negative feedback from one secondaryof transformer Tl to the summation point of thebase of Ql. Zener diode Dl is incorporated intothe signal input network of Ql to regulate thedrive voltage. Zener diode D2, connected betweenthe base and collector of Q2, is used to preventthe backswing of Tl from exceeding the supplyvoltage. When such transients occur, the zeneravalanche causes Q2 to conduct, thus preventingcollector-to-base avalanche. The transistoroperates at its fu l l voltage capabilities within the

+ 65Vvia a transmission line toroidal transformer whichminimizes capacitance and leakage reactance.Parallel transmission lines are used to approxi-mate a true transmission line, providing a unitypower factor (or VSWR) over many frequencydecades.

Source: W. E. Milberger ofWestinghouse Electric Corp.


(MFS-14034)


A SIMPLE, HIGH VOLTAGE PULSE GENERATORFOR WIDE-GAP SPARK CHAMBERS

A low-inductance, high-capacitance, Marxpulse generator uses a coaxial configuration toproduce a 100 kV pulse, with a 2.5 nsec rise time,across a resistive load. The generator design andcoaxial configuration, which minimize internalinductance and suppress external electromagneticradiation, can be used for electromagnetic pulsesimulation and flash X-ray generation.

The Marx pulser (see fig.) employs a capacitorparallel-charging and series-discharging techniqueto obtain the high voltage mult ipl icat ion. A sparkgap chamber provides a series capacitor dischargepath upon triggering of the first spark gap break-down.

The spark gaps of the generator are enclosed ina pressurized nitrogen atmosphere which allows


the charging voltage to be varied by changing thenitrogen pressure. The inner wall of the pressurevessel is painted with a white reflective coating,providing an optical path which permits the un-

HV

T

set near the spontaneous breakdown threshold ofthe first gap, the gap is adjusted so that it breaksdown at a slightly lower voltage than the othergaps.

TriggeElectrode

RC

Re

2W4000 pF 30 kVCharging Resistor

Wide-Gap^Spark x^jChamber '(460 pF) L

Load

HV Probe

JOscilloscope

fired gaps to be irradiated with ultraviolet lightfrom the fired gaps. The capacitors are bariumtitanate cylinders with silver plated ends, and theelectrodes are brass hemispheres 11 mm in diam-eter. To ensure that the operating voltage can be

Source: L. P. Keller and E. G. WalschonArgonne National Laboratory

(ARG-10136)

Circle 5. on Reader Service Card.

HIGH VOLTAGE PULSE GENERATOR PRODUCES FIXED ENERGY PULSE

Power Input Staget

Output Stage1

Magnetic Core, Step-DownPower Transformer

Input Terminal Silicon ControlledRectifier !

PULSE GENERATORS

A unique feature of a new high voltage pulser isan automatic discharge control circuit whichoperates only when the proper spark-producingvoltage is present.

The high voltage pulse generator illustrated inthe schematic produces a controlled, high voltage,fixed energy spark. A fixed voltage for the sparkdischarge is provided by a storage capacitor Clconnected in parallel with a zener diode Dl. Dis-charge of the capacitor through the primary of anoutput transformer is controlled by a separatelypowered control circuit which uses a siliconcontrolled rectifier, SCR1, as a switching device.When the desired capacitor voltage is reached, thezener diode in the control circuit is driven into

conduction to fire SCR2; this operation activatesa relay that energizes a "ready" lamp, indicatingthe circuit is prepared to deliver a fixed energyspark. The charge circuit is manual ly fired by clos-ing a switch, or automatically fired by l ink ingthe switching mechanism to the relay. After eachdischarge, SCR1 is automatically commutated bythe back EMF of the output transformer, andSCR2 is commutated by the ac input to the controlcircuit.

Source: D. L. PippenManned Spacecraft Center

(MSC-12178)


Section 3. Oscillators

LOW POWER, COMPACT, VOLTAGE-CONTROLLED OSCILLATOR

5 Vdc

Control Voltage

A low power, compact, voltage-controlled os-cillator (VCO) has a wide control range, a linearcontrol response, and an output which is com-patible with integrated circuitry.

The VCO(see fig.) is designed with an integratedcircuit containing N A N D gates Gl, G2, G3, and

G4. The oscillator has a linear response over thefrequency range of 1 to 4 MHz for a control volt-age of -1 to -6 V, respectively. The highest fre-quency design limit with a linear response is ap-proximately 5 MHz. The l imiting factor is thepropagation delay of the low power logic.

10ELECTRONIC SIGNAL GENERATORS

The oscillator section is a bistable multivibratorconsisting of G2, G3, D4, D5, R2, R3, Cl and C2.The output is buffered by G4 for fanout purposesto additional circuits. The input network, con-sisting of Gl, D2, D3, and Cl, assures that the os-cillator will start when power is initially applied,and prevents severe power supply transients fromcausing the oscillator to "latch up." CL1 is a cur-rent-limiting diode used to conserve power.

Voltage regulation for the gates, provided by Rland zener diode Dl, prevents undesirable fre-quency deviations which would otherwise occurfrom ripple on the 5 V power supply. Circuitpower consumption is 65 mW at 4 MHz, whenthe control voltage power is a maximum of 11mW.

Assuming that a 5 V supply would have suf-ficient regulation to prevent undesirable frequencydeviation, Rl and Dl could be eliminated and D2changed to a 3 V zener. Subsequent power con-sumption could be reduced to approximately25 mW, with no change in the control character-istics.

Source: J. A. Exley ofIBM


(MFS-20136)


VOLTAGE-CONTROLLED OSCILLATOR

The voltage-controlled oscillator outlined inthe block diagram represents a unique approachto the generation of FM subcarriers and FMmodulation. The VCO consists of an RC oscil-lator, a modulator, and an automatic gain-control

constant if the phase shift in the amplifiers issmall. The design of the oscillator requires abalanced, high input impedance, differentialamplifier with matched transistors that have min-imal drift characteristics.

VCO OutputVjn

ModulationSignal

r1

1

1

Modulator ModulatorAmplifier

Amplifier#1

Amplifier#2

nIIri

AutomaticGainControl

' Oscillator Section IL — — — — — — — — — 1

circuit. The basic oscillator is a phase shifterwhose output amplitude is always constant regard-less of the amount of phase shift. Two of thesephase shifters (amplifiers) are connected in series,and the output of the second phase shifter is in-verted and fed back to the input to produce theoscillations. The feedback loop-gain is controlledby an AGC circuit so that the amplifiers operatein their linear regions with a low-distortion sine-wave output. The frequency of the oscillator isprimari ly determined by the value of the RC time

The modulator section generates a current at theoscillator frequency, the magnitude of which isproportional to the modulating signal. The modu-lator can be considered as an analog multiplier,since its output is the product of an input signalat the oscillator frequency and the magnitude ofthe modulating signal. The modulator exhibitsnonlinear characteristics which serve to negatethe opposite nonlinear modulating characteristicsof the phase-shift oscillator.

Automatic gain control is accomplished by vary-

..OSCILLATORS 11

ing the resistance in the feedback loop of the os-cillator second stage. This resistance is varied bychanging the gate potential of a field effect transis-tor. The AGC amplifier compares the outputsignal amplitude with a reference voltage andsupplies a current pulse.

Source: Spacelabs, Inc.under contract to

Manned Spacecraft Center(MSC-11707)


CONSTANT-AMPLITUDE RC OSCILLATOR

A sinusoidal oscillator has a frequency deter-mined by the RC values of two charge control de-vices, and a constant-amplitude voltage indepen-dent of frequency and RC values. RC elementscan be selected to provide either voltage control,resistance control, or capacitance control of thefrequency.

> V ; BPhase Varying Stage 1 r

A variation of the input frequency changes thephase angle but not the amplitude of V2. Thefirst stage provides a positive phase shift from 0to IT radians, depending on the frequency and thevalues of Rl and Cl. The second stage has a phaseshift of opposite polarity. Therefore, if the base-to-collector and the base-to-emitter transistor

Phase Varying Stage 2

'R3 'R5

V1

Cl

R1

V2C3

'R7 R9

R2

C2

V3

RIO

r±r C4

C5

The basic oscillator circuit has two cascadedphase-varying all-pass stages. As shown in thefigure, bias resistors R3, R4, R7 and R8 arechosen in conjunction with load resistors R5,R6, R9 and RIO to operate transistors Ql and Q2with input-to-collector and input-to-emittervoltage gains of unity. Resistor Rl and capacitorCl form one all-pass network, and resistor R2and capacitor C2 form the second all-pass net-work. The two states are shown ac-coupled bycapacitors C3 and C4.

voltage gains are unity for each stage, and if coup-ling capacitors C3 and C4 have negligible reac-tance compared to capacitors Cl and C2, thecircuit will oscillate at a frequency such that thesum of the two phase shifts is equal to zero.

Source: W. J. Kerwin and R. M. WestbrookAmes Research Center

(ARC-10262)


12 ELECTRONIC SIGNAL GENERATORS

A 225 MHz FM OSCILLATOR WITH RESPONSE TO 10 MHz

A frequency-modulated transistor oscillator isdesigned for use in wideband television transmit-ters. The oscillator circuit, represented in theschematic, is an LC Colpitts tank-circuit con-figuration which provides sinusoidal output wave-forms, even when excited by a nonsinusoidal input .The circuit also provides a high rate of phasechange at the resonant frequency, which has theeffect of producing good frequency stability.

A common-collector configuration for transis-tor Ql is used primarily because the collector isinternally connected to the case. The combinedeffects of case capacitance to ground and heat-sink capacitance to ground provide an effectiveRF ground for the collector.

The varactor Q2 is placed in series with thecoil to eliminate the modulation effects that oc-curred when! it iwas originallyi placed, in. a parallelconfiguration. At high frequencies, there is suf-ficient internal inductance and lead inductance tocause the varactor to enter the series-resonantmode. If this condition were allowed to exist, adrastic reduction in Q would occur, producingunpredictable modulation response.

The problem of applying the modulation signaland the bias voltage to the varactor is solved bythe use of a blocking capacitor Cl and a series-trap tuned to a 225 MHz signal. The trap was de-

signed with a low value Q to avoid undue attenua-tion of the sidebands through the trap and thevideo amplifier to ground.

The dc biasing network is conventional, withQl biased at 40 mA collector current and VBat approximately 15 V. This biasing level enablesthe transistor to operate at a point which producessmall-signal, class-A oscillation.

+c

ideoiput

p-

VB

L2

R5

\l f\\ 13

C4 \

225 MHzModulatedOutput-

ni" :

\' iCl

;C2

^ C3 '

)

~7iTn

R2 ;

,C5(

r

R3

ISource: Auburn University


(MFS-14977)


OSCILLATOR USES TRANSISTOR AS INDUCTIVE ELEMENT

An inability to fabricate suitable inductors withpresent day microminiature component tech-nology places a serious limitation on the design

?VC C

engineer. A new circuit uses a bipolar transistorQ2, operated in a grounded-base configuration,in place of an inductor. The circuit can befabricated with either thin-fi lm hybrid or mono-lithic technology.

The basic oscillator shown in the schematicis a modified Colpitts circuit. Resistors Rl, R2,R7, R8, R3, and R6 comprise the biasing networksfor transistors Ql and Q2, while C4, Cl, and C5are bypass capacitors. R4 and R5 are the loadresistors for Ql and Q2. C2 and C3 form thetuning capacitances, and, in conjunction withQ2 (the inductive transistor), form the feedbacknetwork. Resistor RB, a tuning resistor, variesthe frequency by changing the equivalent induct-

OSCILLATORS 13

ance. For crystal control, Cl is replaced by acrystal, and operation takes place at the series-resonant frequency of the crystal. The value ofinductive reactance j 'XL obtained with thiscircuit arrangement is

j*. = 1 +

where RB is the base resistance, FT is thetransitional frequency, and F is the operatingfrequency.

Source: L. L. KleinbergGoddard Space Flight Center

(GSC-10375)


AUTOMATIC FREQUENCY CONTROL OF VOLTAGE-CONTROLLEDOSCILLATORS

A unique feature of this frequency-controloscillator circuit is the use of optical-capacitivecoupling for isolation of the klystron controlelectrode. The electrode voltage is controlledby a voltage-divider photoresistor whose value

Stabilizing Network

Error Input

tial pair for phase inversion of the amplifiedsignal, without shifting the base operating pointof Q3. Q3 drives the lamp LI and the couplingcapacitor Cl. The meter indicates the lamp currentand acts as an error indicator. The increase in thecurrent through the lamp decreases the resistanceof the photoresistor PR1 and changes the voltageof the control electrode. Because the lamp has arelatively long time constant, the coupling capaci-

-V

ToControlElectrode

approximates the potential of the control elec-trode. This circuit can be used for controlling thefrequency of laboratory oscillators and forstabilizing the pump frequencies of parametricamplifiers.

The circuit shown in the figure is designed tostabilize the frequency of an S-band reflex kly-stron. The error input, derived from a discrimina-tor which compares the klystron frequency witha harmonic of a stable crystal oscillator, is appliedto a stabilizing, lead-lag network and thenamplified with an operational amplifier. Transis-tors Ql and Q2 form an emitter-coupled differen-

To PowerSupply

tor is used to transfer the high frequency compo-nents of the error signal.

Source: R. B. KolblyofCaltech/JPL

under contract toNASA Pasadena Office

(NPO-11064)


Section 4. Analog Signal Generators

CIRCUIT GENERATES COMPLEX WAVEFORMS

A diode generator electronically producesthe complex waveforms of sin (iTsinwt) andcos (27rsino)t) without using series summation.Four circuits alter the input signals in the

(1) Greater Taker "

(2) Lesser Taker'

(3) Level Shifter

(4) Diode Shaper»—VW.

The four basic circuits can be connectedin a variety of ways to produce the same wave-form. They have sufficient flexibility to permiteliminating several resistors, replacing diodes

-V

Output

cos[2irsinut]

-V -V -V

following manner: #1 takes the greater part ofboth input signals; #2 takes the lesser part ofboth signals; #3 splits the positive input into apositive and negative signal of the same wave-shape (level shifter); and $4 rounds off thepositive input (diode shaper). For example, thecircuit diagram shows the development ofcos (27rsino)t). The circuits are so connectedthat the characteristic input waveshapes ofAsinut at point "a" and -Asinwt at point "b"are modified sequentially by each circuit, re-sulting in an output waveform that veryclosely approximates the desired funct ion.

by emitter-follower transistor configurations, andvarying the number of components in thediode-shaper, depending on the particular applica-tion of the generator.

Many functions other than those indicatedhere can be implemented by an empiricalsynthesis of the same building-block circuits.

Source: D. Mead, A. J. McCall, andJ .D .Ca l l ano f

Hughes Aircraft Co.under contract to



SINE FUNCTION GENERATOR

A new sine function generator (see fig.) pro-duces an output signal whose magnitude isproportional to the trigonometric sine of a

given angle, plus or minus a fixed-phase angle.A novel circuit samples the magnitude of a sinewave at a point in its period determined by

14

ANALOG SIGNAL GENERATORS 15

the magnitude of the input signal. The output ofa square-wave generator is filtered in orderto generate a sine wave of the same frequencyas the square wave. Simultaneously, the square

until the next sample is taken. The synchronismcontrol determines the frequency of sampling,which is designed for the anticipated maximumrate of change of the input 6 , and may be as

_hr K IfhSquareWave .Control

ID

t "i

Filter

1 VPhaseShifter

r 1

Gate H3" '̂6 *-V0=K sin (</>+9)

i i» 1^1 l̂ -l

SweepGenerator

i

•VoltageComparator,

iImpulseGenerator

O Input 0 T

wave is used to synchronize a sawtooth sweepgenerator. The synchronized sweep signal isapplied to a voltage comparator which com-pares this input with a voltage that is linearlyproportional to a second input, 6 .

When the value of 9 is equal to the magnitudeof the sweep voltage, the output of the voltagecomparator drives the impulse generator, whichin turn opens an electronic gate for a shortinterval. The sine wave obtained from the filteris phase shifted through a predetermined angle<£ by the phase shifter and is passed throughthe gate when the impulse generator signalis applied. Thus, an impulse whose magnitudeis proportional to sin ( #;+,</>) | is applied tothe sample hold. This sample is the outputvoltage, V0= Ksin( 6 + <t>), which is maintained

great as the fundamental frequency of thesquare wave. The greater the sampling rate,the more accurately the output will representKsin( 6 + <t>) as 0 varies with time.

The static accuracy is not limited by the res-olution (number of turns) of a nonlinear poten-tiometer, such as those used in mechanical sys-tems, nor does the overall accuracy depend onthe length of the interval over which it isgenerated.

Source: T. Bogart, Jr. ofNorth American Rockwell Corp.


(MSC-00255)


CIRCLE-NOTCH GENERATOR CIRCUIT

1 kHzSine Wave

CircleDisplay

. Drive

\

H

l

CRT

o|1 kHzInput

SignalConditioner Integrator

DC Analog Input

A novel circuit generates a blanking signalwhich discontinues a small segment of the circleline on a cathode ray tube (CRT) display. In

Inverter &

tor

BlankingCircuit

order to accomplish this, a clock pulse is condi-tioned and fed into an integrator that producesa negative ramp output. A positive dc analog


inpu t is compared with the ramp output by acomparator whose output pulse is a funct ionof time. The comparator output is invertedand conditioned through a one-shot mult ivibratorfor an adjustable pulse output .

A circle is displayed on the CRT by applyinga clock-controlled sinusoidal signal on thevertical and horizontal deflection circuits. Sincethe periods of the ramp and the sine waveare the same, each r amp ' i s ' equa l to 2^ rad ofa circle and the ramp amplitude becomes a func-tion of radians. Calibrating the ramp amplitudeand the dc analog input in volt/radian enables

the comparator to establish the point of theperiod for a corresponding radian. The one-shot mult ivibrator accepts this varying signaland generates an adjustable pulse width equalto the number of radians that are blanked outon the circle.

Source: O. Hayakawa ofNorth American Rockwell Corp.


(MSC-15846)

Circle 1.4 on Reader Service Card.

DIGITAL-VOLTAGE CURVE GENERATOR

A curve generator produces an easily con-trolled, precisely repeatable curve for any single-valued function of voltage versus time. Thecurve generator (see fig.) consists of a clocked,feedback shift-register; a large-scale, integrated-circuit diode matrix; a counter; and a digital-to-analog converter.

r I Memory Elements

ates designated output states in accordance witha feedback funct ion. Entries in this matrixare the selected states of the shift registerwhich decrease the output of the counter. Suc-cessive states appear for a fixed duration oftime, whereas selected states are separated intime in accordance with the desired curve.

.Binary Down Counter

FeedbackFunction

•«i

4(

—

>•

M

1*1

I mr1-i •1*r

„

„

ii

AND/ORMatrix

ii

Z-J

.V2

•

ZB

LadderNetwork

Amplifier

I

I Feedback Shift Diode Selection .I Register I Matrix I

Equal changes of voltage, sufficiently smallin value and number to reflect small changesin the curve, are held for varying time durationsin accordance with the desired shape of thecurve.

Time is quantized by the feedback shift regis-ter and the diode selection matrix, which gener-

Digital-to-Analog

i Converter i

Several large-scale integrated circuits com-prise the AND/OR diode selection matrix. Thepurpose of this matrix is to convert the non-weighted code of the feedback shif t registerto a series of nonuni formly spaced time pulses.The output of the matrix decreases the outputof the binary down counter, for example, to

ANALOG SIGNAL GENERATORS 17

produce a monotonically decreasing funct ion .The output of the binary counter is applied toa digital-to-analog converter in order to derivean analog equivalent of the binary signals. Ananalog output ampl i f ier is used to set the operat-ing levels over which the curve will vary.

Source: M . P e r l m a n o fCaltech/JPL

under contract toNASA Pasadena Office

(NPO-11104)


Section 5. Square Wave Signal Generators

VARIABLE PULSE GENERATOR SWITCH

The variable pulse generator delivers squarewave pulses of 28 Vdc to operate conventionalsolenoid valves. The pulse width is adjustableover the range of 10 to 40 msec, and the interval

22.5 Vdc

28 Vdc OutputPower

between pulses is adjustable from 8 to 350 msec.The complete circuit consists of a solid stateflip-flop (Ql and Q2), a triggering unijunctiontransistor Q3, and output amplifiers Q4 and Q5.The pulse-forming circuit is powered by an in-dependent 22.5 V battery, and is assembled fromreadily available components. Pulse width iscontrolled by adjusting a 100 kft potentiometerRl ("On Time"); the interval between pulses("Off Time") is similarly controlled by a 500 k 0potentiometer R2.

This circuit can be used in hydraulic andpneumatic flow-control systems where criticalflow timing is required. It can be used forsingle-flow operations or, with a suitable ar-rangement of relays, as a closely sequenced,multiple-flow control.

Source: J. D .Gi l le t to fNorth American Rockwell Corp.


(MFS-91895)


SQUARE WAVE GENERATOR FOR HIGHFREQUENCY APPLICATIONS

A new pulse generator provides high fre-quency operation and good stability. Only twocomponents govern the frequency, and only onecomponent determines the pulse width control.

Ease in changing the frequency and pulsewidth makes this pulse generator (see fig.) wellsuited for remote electronic control operations.

The circuit operation begins with Q2 in con-


V in 12Vdc

o +duction and Ql out of conduction. (Ql is heldout of conduction by the voltage drop acrossR4). When the charge on capacitor Cl reachesa sufficient voltage to turn on Ql, Q2 is turnedoff by the reduced current through R5. Thevoltage drop across R4, resulting from currentflow through Ql, further biases Q2 out ofconduction. Under these conditions, the inputimpedance of Ql drops sufficiently to dischargeCl through R2, Ql, and R4. Ql then goesout of conduction, Q2 goes into conduction,and the cycle is repeated.

Source: E. R. Quinn, F. E. Downs, andR. D. Lynch of

Lockheed Electronics Co.under contract to

Manned Spacecraft Center(MSC-91061)


SQUARE WAVE GENERATOR HAS VARIABLE DUTY CYCLE

A square wave oscillator circuit, constructedwith an integrated circuit "AND" gate module,;a resistor, and a capacitor, provides an outputwith a frequency range from 1 Hz to greater

Off/On IGateQ

while module 4 is a pulse-shaping circuit. Module1 provides a K rad phase shift and is usedto gate the oscillator on and off. Modules2 and 3 are operated as high-gain amplifiers,

1

Output

_j

than 1 MHz. The oscillator can be used togenerate clock pulses for any electric circuitrequiring a square wave pulse with stability of5 X 10 4/K. The oscillating pulses can be syn-chronously gated on and off without any addi-tional circuitry.

The components of the oscillator, shown inthe block diagram, can be integrated ontoa single chip. This form of circuit fabricationimproves temperature stability, since the RCcombination is an integral part of the circuitmodule.

Modules 1, 2, and 3 are part of the 1C module,

with R as the input resistance and C in the feed-back loop.

The frequency of the "AND" gate oscillator iseasily adjusted throughout the wide frequencyrange by selecting the proper RC combinations.In addition, the gated oscillator can be gatedon and off with a control pulse. The oscillator'swaveform is synchronous with the starting edgeof the control pulse.

Source: W. H. MillerGoddard Space Flight Center

(GSC-10836)


SQUARE-WAVE SIGNAL GENERATORS 19

SINGLE TRANSISTOR CIRCUIT BOOSTS PULSE AMPLITUDE

A simple circuit provides a voltage pulsegreater than that normally available from emitter-follower circuits to drive a 100 W transmitter.Capacitor storage, followed by common-baseswitching, is accomplished with only one transis-tor.

During circuit operation, capacitor Cl (see fig.)is charged through Rl and R2 to the supply linevoltage VI. With no input pulse, both the emit-ter and base of the transistor are at the samepotential and the collector is cut off. With aninput pulse V2 present, the potential of Cl withrespect to ground is increased by V2. The emit-ter becomes more positive than the base, andthe transistor is switched on. This action pro-duces an output pulse, V3, equal to VI + V2(minus small losses in Cl and the transistor.)

In order for Cl to reach approximate ful lcharge between pulses, the ratio of charging in-terval to charging time-constant must be much

greater than the ratio of discharge intervalto discharge time-constant. The circuitproduces an output waveform at about twicethe amplitude of the supply line voltage V1.

'VI

V2 |V3=V1+V2

Source: M. W. Matchett and T. Keon ofCutler Hammer


(GSC-501)


Section 6. Special Function Signal Generators

400 Hz NOISE GENERATOR

The noise-adder circuit shown in the schematicconditions and amplifies noise from a randomnoise generator and adds it, in series, to two

400 Hz,</>1 o

Shield

Ground O

Noise In

applied to two operational amplifiers throughseparate input filters (one section is shown in thefigure). The combination of the input filters and

OperationalAmplifierNo. 1

phases of a power source that supplies amagnetic tape recorder.

Noise from a random noise generator is

the operational amplifier circuits increases thelow-frequency response of the adder circuits,providing an overall pass band (flat within 3 dB)


of 2.3 kHz to 1.3 MHz for the noise. The noiseis amplified to a level of 20 dBm and added inseries with both phases of the 2-phase,400 Hz power source across load resistors; theseresistors provide the required 250 ft outputimpedance of the power source. This circuitcan be used whenever controlled noise mustbe introduced into a low impedance powersource.

Source: O. Hergenhan, G. A. Cutsogeorge, andE. W. Dusioof

Radio Corp. of Americaunder contract to



CONSTANT FREQUENCY, VOLTAGE-TO-DUTY-CYCLE GENERATOR

Bistable BinaryUnijunction TransistorOscillator V2

The characteristics of a unijunction transistoroscillator and those of a bistable binary havebeen combined in a very simple circuit toproduce a constant-frequency voltage-to-duty-cy-cle generator. With its capability of producingduty cycles from zero to unity, this generatorshould be very useful in applications involvingefficient regulation of dc converters supplied bywidely varying voltages. Important advantagesof this generator are its simple structure andits very low power consumption, especiallyif a unijunction transistor with very low leakagecurrent is used.

When the uni junct ion transistor Ql (see fig.)

is fired, capacitor Cl discharges to zero volts.The base current required to turn Q2 on isnegligible compared to the current in Rl, andthe voltage drops across R3 as well as the base-emitter junction of Q2 are negligible comparedto the breakdown voltage of the zener diode Dl.

Whenever the level of the voltage at point "a"is below that of VZD , Q2 is cut off, since nocurrent is supplied to its base. Simultaneously,base current for Q3 is provided via R4 and R6,Q3 is turned off, and V0 becomes zero. How-ever, when the level of the voltage at "a" equalsor exceeds VZD, base-current is provided forQ2, causing it to tu rn on. Q3, which is re-

SPECIAL FUNCTION SIGNAL GENERATORS 21

verse biased by the voltage across speed-upcapacitor C2, is turned off , and the voltagelevel rises to V2. If the input voltage is nottoo low, the frequency of oscillation, whichis mainly a funct ion of the product (Rl + R2)XC1, is relatively constant.

Source: l .M.H. Babaa ofDuke University

under contract toNASA Headquarters

(HQN-10070)


LINEAR DC ANALOG VOLTAGE-TO-PULSE WIDTH CONVERTER

This circuit converts a dc analog input signalto an output pulse whose width is proportionalto the input signal voltage. The circuit rep-resents an improvement over previous pulse-

is charged by the analog input signal and dis-charged through the constant-current generatorQ2 and Dl when a pulse is applied to Ql. Thecomplementary flip-flop operates for one corn-

Trigger Pulseo

vcc

Q—DC Analog InputSignal o K |« o Output

width converters with regard to design sim-plicity, efficiency, linearity, accuracy, andtemperature stability. It would be particularlyuseful as an analog-to-digital converter wherelow power, ruggedness, reliability, and goodlinearity are prime requirements.

The converter (see fig.) consists of a com-plementary, monostable flip-flop controlledby the constant-current discharge of the temper-ature compensated capacitor Cl. This capacitor

plete cycle with a period (pulse width) propor-tional to the dc analog input voltage. Thelinearity of this circuit is relatively independentof temperature variations over a range from253 to 343 K (-20° to 70° C). Its power drainis less than 100 mW.

Source: W. R. CrockettGoddard Space Flight Center

(GSC-556)



CONSTANT-FREQUENCY, VARIABLE DUTY CYCLE MULTIVIBRATOR

A constant-frequency pulse source has aduty cycle that can be adjusted by an externalinput signal. Applications of this pulse source in-clude a switching-mode voltage regulator and aswitching source for control systems. The circuitcan also be used as a pulse-duration modulator;

In normal circuit operation, transistor Q2is on and capacitor Cl is charged to potentialVI. With Q2 on, VI is applied to the base ofQl, turning it off. The current source, formedby Q3 and its bias resistors, causes thispotential to increase linearly with time.

Since VI and V2 are derived from the dif-ferential amplifier, the sum, VI + V2, is con-stant. Thus, the frequency of operation is con-stant, but the duty cycle (or equivalently,the off-time of Ql) is a linear function of VI.VI is a linear function of the control inputsignal. The duty cycle can be controlled at aconstant frequency. Diodes Dl and D2 serveto decouple the charging of Cl and C2 fromthe positive supply. R3 and D3 provide a ref-erence inpu t so that the duty cycle is a funct ionof the difference between the control input andthe reference voltage of D3.

ExternalSynchronization

+ V

Source: J. E. Johnson ofUniversity of Michigan


(XGS-10033)


ULTRASTABLE REFERENCE PULSE GENERATORFOR HIGH-RESOLUTION SPECTROMETERS

A solid-state, double-pulse generator has apulse amplitude-temperature coefficient of0 to 8 ppm/K. The pulser generates si'gnalsthat rise in 15 nsec, remain flat-topped for40 Msec, and then fall exponentially to the base-line in 250 Msec. The pulse rate can be variedfrom 0.1 to 1000 pulses per second in nine steps;and the amplitude of the two pulses can be setindependently, from 5.5 to 700 mV, by useof a seven-bit, precision, R-2R attenuator. Thecircuit of the pulse generator includes anoscillator, followed by a flip-flop that gener-ates two square waves T rad out of phase. Afterthe signal is applied to pulse shapers, theoutputs of the shapers are applied to emitterfollowers that are normally "off." (For negative

outputs, they are normally "on.") The emitterfollowers alternately saturate and thenreturn exponentially to their initial condition.The 18 V emitter signals are attenuated by a7-bit ladder and mixed at the output acrossa 100 £2 resistor to produce ,the proper wave-form. Since the temperature coefficient is only2 ppm/K, the power has no appreciable effecton the stability of the output pulses. The at-tenuator also has only a second-order effecton the stability of the output pulses. The varia-tions in saturation voltage due to fluctuationsof temperature and base drive are quite smallcompared with 18 V. Thus, instead of producingthe low-level signals directly, the 18 V pulsesare generated and subsequently attenuated to

SPECIAL FUNCTION SIGNAL GENERATORS 23

18.6V

18.6V

Shaper L 1 Osc i I lator 1_TL

+ 18 V '

7-Bit R-2R Attenuators

5 5-700 f\ B f\ Rise time: 1 5 nsimV I Vr\J V FlatT°P: 40Mse

T —— —J ^-J ^^J ^^- c«ll T: icrt

,-* T x

i "Ul

A

the desired millivolt level, thereby reducing theinstability of the output signals by a factorwhich ranges from 25 to 3300. This reductionis the basic concept underlying the stability ofthe pulser.

Rise time: 1 5 nsec.c.

Fall Time: 250Rate: 0.1 -1000 pulses per secondRout: 92ft

Source: M. G. Strauss, L. L. Sifter,F. R. Lenkszus, and R. BrennerArgonne National Laboratory

(ARG-10364)


NASA-Langley, 1971

NATIONAL AERONAUTICS AND SPACE ADMINISTRATIONWASHINGTON, D. C. 20546

OFFICIAL BUSINESSPENALTY FOR PRIVATE USE $300

FIRST CLASS MAIL

POSTAGE AND FEES PAIDNATIONAL AERONAUTICS AND

SPACE ADMINISTRATION

W Undeliverable (Section 158Postal Manual) Do Not Recurn

*" ',

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Details on the availability of thesepublications may be obtained from:

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