US2482803A - Electronic signal shaping circuit - Google Patents

Description

Sept. 27, 19 9- c. H. SMITH, JR., ETAL 2,482,303

ELECTRONIC SIGNAL SHAPING CIRCUIT Filed Sept. 13, 1946 is u o l5 25 1| SIGNAL SOURCE fi W l- |2 l8 I3 A SIGNAL FROM SOURCE n 5+ I B AVE. PLATE I SYMMETRICAL VOLTAGE V SQUARE WAVE OUTPUT MIN.PLAIE 1 VOLTAGE I B+-- AVE.PLATE UNSYMMETR|CAL C VOLTAGE SQUARE WAVE OUTPUT MIN. PLAT E VOLTAGE grvue/wbow CARL HARRISON SMITH JR. MILTON L KUDER Patented Sept. 27 1949 ELECTRONIC SIGNAL SHAPING CIRCUIT Carl Harrison Smith, Jr., Va, and Milton L. Kuder, Washingttm, D.

Application September 13, 1 94's, Serial No. 696,980

(01. ear-2r) (Granted under the act of March .3, 1883, .as amended April 30, 1928 337 0,. G. 757

3 Claims.

invention relates to electrical signal generating systems and in particular to systems for producing symmetrical square-Wave signals over .a wide frequency range and independent of variations in power line voltage.

many of the present forms of electrical square-wave signal generator systems, a sinus- .oidal signal having thefrequency of the desired square wave signal is first generated andthen applied to -a-cl=ipping stage or stages wherethe crests of the sinusoidal signal areclipp.ed 01f. For biasing considerations in the clipper stages it has usually been necessarywith previous systems to maintain the amplitude of the sinusoidal signal applied thereto substantially constant otherwise a non-symmetrical square =wave output is .obtained. To maintain such a degree of constancy in prior systems despite fluctuations such as in supply voltage, special oscillator control tubes or a regulated power supply were required.

Accordingly it is an object of the presentinvention to provide a signal generating system for producing symmetrical square wave signals independently .of fluctuations in the voltages supplied thereto. g

Another object of the present invention is .to provide in a square Wave signal generator system employing a clipper tube, bias adjusting means for the clipper tube maintainingsymmetr-ical square wave signal output.

Other and further objects and features of the present invention will becomeapparent upon a careful consideration of the accompanying description and drawing.

Fig. in a schematic diagram,.pa rtly in block,.

of a typical embodiment of ithe'features of the invention. "1v

Fig. 2 is'a s-eries of waveforms taken to illustrate more fully the operation of the circuit of Fig. l and the method of maintaining a substantially symmetrical square wave voltage output.

In accordancewiththe fundamental concepts of the present invention a s'igna'l generator device for producing square wave signals is provided in which a symmetrical square wave output is maintained over a wide frequency range despite variations in voltages supplied thereto. Broadly, a reference frequency signal of a sinusoidal character is provided-to control the operation of the system. This sinusoidal signal is then applied to a clipper tube Where the positive and negative crests are removed. Bits for the clipper tube is supplied in part from the plate circuit thereof through albias transfer network. This bias is varied automatically in dependency on the shape of the output square wave to maintain a central :cl-ipping-regirm resulting in the production of symmetrical square wave signals. V

With reference to the particular embodiment oi Fig. 1, a clipping tube L0 is employed :as an overedriven voltage amplifier obtaining its grid drive voltage from :a signal source H through .a coupling-capacitance. :Signal source l is preferably adapted to produce a sinusoidal signal having a frequency equal to that-of'the desired square wave output signal. Where it is desired that the frequency of the square wave be variable over a frequency range, the signal source 'll :be

capable of covering that frequency range. The

amplitude of the sinusoidal signal is preferably constant, however the clipper circuit will operate satisfactorily despite wide variations of input signal amplitude :and frequency such as would accompany fluctuations in the supply voltage.

The anode of tube II] is returned to a source of positive voltage through anode load resistance M. Voltage fluctuations at the anode of tube Ml are coupled to the output terminals l 5 through a coupling (capacitance 1B andv the ground return lead. I

Bias for the control grid of tube i0 is obtained in part from the positive supply through anode load resistance l4 and grid coupling resistance I1 and in part from the capacitance 1'2 which becomes charged as .a result of grid current flow in tube l1] during .a portion of the sinusoidal input signal.

The sinusoidal signal from source ill as represented by waveform A of Fig. 3 drives clipper tube Ill to alternate conditions of heavy anode circonductivity and anode circuit cut-off. The positive crests of the input signal drive the controlltnr id of tube 18 positive with respect tothe cathode resulting in control grid conduction and monster-lent loss of signal voltage across limiting resistance 13- to produce the flattened out nega- Ftiue portions of Waveform B, Fig. 2. 0n the opposits half cycles of the driving signal the -clipper tube all! is driven to a condition of anode :cir-

cuit cut-ofi to produce the flattened positive portions of waveform .13.

Mom wavetorm Bit is evident that :the circuit as ltliiHS far described produce a symmetrical square Wave, having durations of the negative and the positive flattened portions only when the bias of tube I0 is critically adjusted so that the average grid potential :is midway between required for anode current cut-on and for zero bias condition and is brought about by the action resistance! 1 to offset "the charging of capacitance l2 during the periods of grid current flow. When the average bias voltage of tube It] is not equal to this mid-value, an unsymmetrical waveform may be produced such as that of C, Fig. 2 in which the lower flattened portions are of shorter duration than the upper flattened portions.

To minimize fluctuations in the average bias voltage for tube 10 as a result of variations in the amplitude of the signal from source II and attendant alternation in the average grid current drawn by tube I 9, the grid coupling resistance I1 is returned to the anode of the tube. Resistance I1 is purposely made large so as to operate with capacitance l2 as an integrator circuitto hold to a minimum the amount of the output square wave fed back to the junction point I8 yet permit flow of a unilateral charging current for capacitance 12 to counteract the charging thereof due to the flow of grid current within tube III. In typical operation, an increase in the amplitude of the signal from source ll would tend to raise the portion of the input signal of waveform A utilized for the production of the square waveform and consequently shorten the conduc tivity period of the tube l0. Such operation would result in the production of the unsymmetrical square wave signal of waveform C hav ing a raised average level. This distortion of the signal is counterbalanced by the action of the connecting path between point [8 and the anode of tube Ill. The attempted rise in average potential at the anode of tube It] raises the potential towards which capacitance l2 charges during the time interval that the control grid of tube I is non-conductive and hence tends to adjust the bias to restore the desired condition in which the central portion of the signal from source ll causes the production of the output square wave.

Satisfactory operation of the apparatus of the invention constructed in accordance with the schematic diagram of Fig. 1 was realized with an output signal from source I 1 variable over the frequency range of 2000 to 50,000 cycles per second and over the amplitude range of 20 to 200 volts with the following circuit constants:

Electron tube-Type 681-17 Anode voltage supply-250 v. v Capacitance I2--0.25 microfarad Resistance l3--100,000 ohms Resistance Id-22,000 ohms Resistance Il-4=.5 megohms From the foregoing discussion it is apparent that considerable modification of the features of the present invention is possible and while the device herein described and the form of apparatus for the operation thereof constitutes a preferred embodiment of the invention it is to be understood that the invention is not limited to this particular device and form of apparatus and that changes may be made therein without departing from the scope of the invention as defined in the appended claims.

The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalities thereon or therefor.

What is claimed is:

1. A generator device for producing symmetrical square wave electrical signals, comprising; a signal generator device for producing sinusoidal signals of variable amplitude having frequency 4 correspondence with the frequency of the desired square wave signals, a clipper circuit comprising an electron tube having anode, cathode, and control grid electrodes suitable for overdriven amplifier operation, an anode voltage supply for said tube, coupling means transferring the sinusoidal signal to the control grid electrode of said electron tube in sufiicient amplitude to consecutively drive said electron tube to anode current saturation and anode current cutoff, said coupling means comprising a series-connected combination of a capacitive element and a resistive element whose free end is connected to the grid electrode of said electron tube, an output circuit operatively connected to the anode electrode of said electron tube and to the anode voltage supply therefor, and a resistive element operatively connected between said output circuit and the input circuit for feed-back to said input circuit of a voltage proportional to the average voltage existing in said output circuit whereby an average voltage of substantially zero volts is maintained in the input circuit at a point between the series connected capacitive element and the resistive element and whereby the square-wave voltage signals developed in the output circuit is maintained substantially symmetrical despite frequency and amplitude fluctuations of said applied sinusoidal signals.

2. A generator device for producing symmetrical square wave signals comprising a sine wave signal generator, a clipper circuit fed by said sine wave generator comprising, an electron tube having an anode, a cathode, and a grid, a source of anode supply potential, a load impedance connecting said anode to said supply potential, means including a series resistance coupling the output of said sine Wave generator to the grid of said tube, a second resistance connecting the anode of said tube to the grid thereof through said series resistance, a condenser disposed within the grid circuit of said tube in an integrating relationship with said second resistance, said second resistance and said condenser cooperating to change the grid bias on said tube in response to changes in average anode potential on said tube and in a sense corresponding to the sense of anode potential changes.

3. A clipper circuit comprising an electron tube having an anode, a cathode, and a grid, a source of anode supply potential, a load impedance connecting said anode to said supply potential, a pair of serially connected resistance elements connecting the anode of said tube to the grid thereof, a condenser, one plate of which is connected to the junction of said resistance elements, the other plate of said condenser serving as an input terminal to the circuit, one of said resistance elements and said condenser cooperating to change the grid bias on said tube in response to changes in average anode potential on said tube and in a sense corresponding to the sense of anode potential changes.

CARL HARRISON SMITH, JR. MILTON L. KUDER.

REFERENCES CITED UNITED STATES PATENTS Name Date Schlesinger Apr. 4, 1939 Number

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