US2441579A - Stabilized multivibrator - Google Patents

Description

May 18, 1948. i D. E. KENYON 2,441,579

v I STABILIZED MULTIVIBRATOR I Filed Jan. 6, 1943 29 gal E, I FIG. 3.

. uivEN'roR DAVID E. KENYON ATTORNEY Patented May 18, 1948 STABILIZED MULTIVIBRATOR David E. Kenyon, Smithtown, N. Y., assignor to The Sperry Corporation, a corporation of Delaware Application January 6, 1943, Serial No. 471,518

9 Claims. (01. 250-36) My invention relates to circuits for electric discharge devices and concerns particularly relaxation oscillators.

It is an object of my invention to provide stabilized oscillators, the operation andfrequency output of which are substantially unaffected by variations in supply voltage, load impedance, anode voltage swing, or tube characteristics.

It is also an object of my invention to' provide improved multi-vibrator circuits.

Other and further. objects and advantages will become apparent as the description proceeds.

, In carrying out my invention in its preferred form, I provide a pair of electric discharge devices which may take the form of triode vacuum tubes with conventional capacitance-resistance cross-coupling between the anode of each tube and the control electrode or grid of the other.

tube. However, I provide a variablebias for the control electrode of each tube, the magnitude of which is controlled by the circuit of the other tube. In this way, I cause the voltage available for discharging the coupling condenser to vary in proportion to the extent'the control electrode voltage is driven negative during each oscillation. By maintaining a fixed ratio between these two magnitudes, I produce constancy in the time duration that each tube is maintained nonconducting and thus stabilize the multi-vibrator circuit by producing constancy of its frequency of oscillation. p

In one form of circuit illustrated inthe drawings, I provide rectifiers coupledto the anode of one tube for supplying the control electrode bias for the other tube. In another form of my invention, as illustrated, I provide cathode resistors in the circuit of one tube for providing control electrode bias for the other tube.

A better understanding of my invention will be afiorded by the following detailed description considered in connection with the accompanying drawings, and those features which are believed to be novel and patentable will be pointed out in the claims appendant thereto.

In the drawings, 7

Fig. 1 is a circuit diagram of one embodiment of my invention employing rectifiers for providing bias,

Fig. 2 is a circuit diagram of another embodiment of my invention in which cathode resistors are employed for providing variable bias, and

Fig, 3 is a .graphexplanatory of theprinciple of operation of the apparatus.

Like reference characters are used throughout the drawings to indicatelikeparts.

Generally speaking, the frequency of operation of multi-vibrators is determined not only swing, since these factors affect the discharging rate of the grid condensers, the shapeoi the discharge curve and the depth to which the grid potential is driven. In order to stabilizethe oscillation and make the frequency independent of the factors mentioned, I arrange the control electrode circuits sothat the effects of variations in anode voltage swing are compensated. For example, I employ variable bias which varies with anode voltage swing.

In the arrangement illustrated in Fig. 1, variable bias is provided by asymmetrical elements, shown as rectifiers, coupled to, the anodes of the discharge devices, as will be explained more in detail hereinafter. The apparatus illustrated in Fig. 1 comprises a pair ofelectric discharge devices ll and lz, each having anodes l3 and [4, control electrodes or grids I5 and I6, and cathodes l'! and I8, respectively. The control electrode I5 is cross-coupled by a coupling condenser 19 to the anode I4, and similarly, the control electrode I'G is ,cross coupled by a condenser 20 to the anode l3. Grid resistors 2| and 22 are provided. The grid resistors, however, are not connected to a point or fixed potential but to separate, variable-voltage bias sources. The bias voltage source for the control electrode [5 comprises a rectifier 23 coupled to the anode l4, and the bias source for the control electrode [6 of the discharge device 12 comprises a rectifier 24 coupled to the anode l3 of theopposite discharge device I I. The rectifiers 23 and 24 may, if desired, be electric discharge devices of the diode type.

The discharge devices I and [2 maybe triode vacuum tubes as shown and described, and the rectifiers 23 and 24, may be diode vacuum tubes, but it will be understood that my invention is not limited thereto. u

As in conventional multi-vibrator circuits, each of the tubes M and I2 is provided with load impedance, represented by the anode resistors 25 and 26. A pair of voltage supply terminals 21 and 28 is provided which may be connected to the positive and negative sides, respectively, of a voltage source, such as a B battery 29, the negative side of which may be grounded. In the arrange'mentillustrated in Fig. 1 the oathodes l1 and 18 are directly connected to the negative supply terminal 28, and the resistors 25 and 26 are connectedin series with the anodes l3 and I4, respectively, to the positive supply terminal 21.

In order to supply direct-current or uni-directional bias voltages proportional to the alternating potentials of the anodes I3 and I4, respectively, coupling condensers 3| and 32 are interposed between the anode l l of'the device I2 and the rectifier"23," and between theanod'e I3and the rectifier 24. For supplying positive bias voltage as shown and described, the rectifiers 23' and 24 are so connected that their cathodes serve as the output terminals to which the grid leak 3! and 32. Filter circuits comprising resistors 33 and 34 and condensers 35 an'd '35, respectively;I-

lo-device to become non-conducting as the first decircuits the discharge devices become alternately vicebecomes conducting. As the coupling con- 1 denser discharges however, the control electrode resistors 2| and 22 are connected- The--rect-ifier'--; anodes are connected to the"couplingcondensersmay also be provided. The time constant of the elements 32 and 34 is preferably large incom peak alternating voltage 'or 'thecomplete anode 7 Voltage swing; For example; the =resistors 33 and 34 may be replaced by twoadditibrralrectifiers 23A and 24A, respectively; This connection may be accomplishe'win 1 by' providing change over switches Sfancl- S2" with switch bladesg which when throwrrin the upward position respectively connect the -ano'de-- of' the*-reetifie'r 23 -to the cathode" of rectifieiflfiei "and the =anode of therec'tifier 24 tothe cathode 'of- -therectifier 24A The *rectifiers 23A and '24-A have their anodes groundedzj I p Whenthe switches S1 *and Sal-"are transferred from theposit-io'n' illustrated to the upward posi tion,'- so"th'a t' the re ctiflrs23Kand"-24A are con-'- neoted, the rectifieFcircuitstogether with the coupling condensers '3 I" and 32 act as'voltag-e donblers: The'f recliners-23fi-rand 24ie -preven-tthan'odes of therectifiers 23 and"24 fronr falling below ground' potential. Consequently; 'the con'-' densers 3 Iand 32-" are charged" whenever the 'po tentials of 'tlfe"anodes--I3 'and I4fall'; and the charges accumulate'd during the negative half cycles ofanodevoltagepass through the'rectifiers 23" and 24- to'the condensers "35 and 36 during the positive'ha'lfcycles'pf' ano dc voltage I at l theanodes I 3 and'- I4: The result is tha-t"-the *condensers 3 5"and36"areprogressively charged with higher andliigher'p'otential's'; until the condenser 35 has reached 'a potential equallin'g thevoltage swing of the anode I4 and the'*condenser36 -has reached "9, potential "equalling?the voltage swing of the "anode I 3." 'rne-eondensers 3' I f 32', 35 and 35 are relatively-large so thatnoappreciable va'riationin' the accumulated charge takes place so long'asther'e' is no change in the voltageswing of the -devioe-which--has been non-conducting gradually rises toicut-oii, causing the latter device to become conducting and to drive the control electrode of the first device negative beyond cu t-off, Thus, each discharge device tends to approacha quiescent condition in which it is conducting, but in so doing it extinguishes the current. new 'inithefother device; If the control electrodes 'arefbias'ed to ground'potential :or' to some other fixed potential the timerequired for the coupling Jcondenser to discharge sufiiciently to permit l the-"control:electrod'e to' rise to cut-off is ivariedvlbyw' various? factors: and these factors, thereforerinfiuencetheinon-conducting period of the dischargesdevi'ce and "-theoscillation irequ'encywfithe circuit; The :charge": collected by the coupling condenser :rdepen'ds'iupon" the -magnitud'e' 'of :thersupply wolta'ge: source 2 9 and the extent o whichahevcontrol electrode'is driven negative dependsrupon the voltage swing of the anode ofthe* other device; whichgi in turn, depends upon the load impedance' and A the 1 characteristie curve oflthe discl-rarge;device." For a given load resistance the anode voltage". swing depends upon the-sane de cathode "current or discharge rurrent o-fithe device:- The'effect'of these factor-s isovercome -in':accordancewith my invention becausethe control electrodes are separately biased by' connecting them to bias points the potentials" fiwhich vary to? compensate for variations in h anodvoltagefiswing of the discharge device whi'ch'corrtrols the control electrode ofthe otheraievice:

Assuming thet at the instant of initial considratio hie-discharge device "I I is :conducting andthe discharge device I 2 i's -non-conducting,

by the supply voltage of source 29 sincelthe anode I 4- isat the qootential or the; positivesupply terminal 2 i and the control-' electrodel 5 ii is substantially at zero: on ground: potential. Owing to the characteristics "of the discharge devices I I and I 2 the control electrode potential cannot rise above zero!" The potential of the cathode of the rectifier 23 1s aea value E1 which-is the value -ofth anode voltage swing of the anode IQP -Cfirrent tendstonew: inthe grid leak resistor 21fbut for the -reason ju'ststated, the control electrode IB rem'ains at Zer or ground potential.

At some -later instanti wh I the- -potential-of" the control electrode Ifi has risen to' cut oft; the discharge device I2 becomes cond" "ing,.;-abr uptly, itsanodevonage faiis abr-uptly y new 'of-eurrent in the load impedanee "2t; and the potential of the control electrode I5 is "driven sharply negative The v 'alue of the negative potentiar of w-hihthe corrtroi electrode I5 is instantan ously repres'erzdaed1as?E2. In

*3 the"- bias potential provid'ed by the condenser 35 is represented as Ei -and th'e negative anode voltage swing throng --Whi'6h'-'th control electrode I5 has' be'eri drive Ea?" The voltage chaiige acting -in thet discharge E1+E2 and the condenser 19 tends to discharge along a curve 21 (Fig. 3) whichis asymptotic to the value of E1. The reason for this will be apparent from a consideration of the nature of the condenser discharge.

The discharge curve of a condenser representing the change in voltage across, the plates produced by a disturbance changing the voltages acting in the discharge circuit of the condenser is determined by the difference between the voltages in the discharge circuit before and after the disturbance. In the case of the coupling condenser l9, this change in voltage is the sum of the bias voltage provided by the condenser 35, represented by the symbol E1, and the anode voltage swing of the discharge device l2, represented by the symbol E2. In Fig. 3 the potential ofthe control electrode IS with respect to ground is represented by the discharge curve 31, which is drawn with voltage measured in the vertical direction and time in the horizontal direction. While the discharge device II is still conducting, the potential of its control electrode is fixed at zero, because electron fiow in the device l I would prevent its control electrode from becoming positive, and the bias potential E1 provided by the rectifier '23 and the condenser 35 has no eifect on the condenser l9. Then at the instant the device it? becomes conducting the potential ,of the control electrode is driven negative through the voltage E2. The control electrode is now free to float at the potential determined by the coupling condenser charge. One plate of the condenser 19 is now efiectively connected through the grid leak H to the cathode of the rectifier 23 which is at E1 volts; the other plate, connected to the anode M of the device l2, must fall E2 volts. The total change in voltage acting in the condenser discharge circuit is therefore E1+E2, and the discharge curve 3! is asymptotic to the line E1 in Fig. 3. For convenience, the difierence between zero potential and the actual cut-oif potential of the control electrode is disregarded since the negative voltage swing is made very large in comparison with the actual cut-off voltage. V

The time required for the potential of the control electrode to rise to the value zero, represented in Fig. 3 by the symbol it, determines the time that the discharge device ll remains non-conductive, If the circuit conditions should be changed by reason of a change in voltage supply, in the impedance of the load impedance 26, or in the characteristics of the device 12, E1 and E2 will change in the same proportion since they have been made equal. The discharge curve31 will become more or less steep than is illustrated in Fig. 3. However, the time durationtwill remain unchanged. Since the curve 31 is exponential, the time required for the ordinate to rise to a fixed proportion of the total change is constant even though the total change in voltage may be varied. Consequently, the non-conducting period of the discharge device H is stabilized and is independent of the various factors mentioned which vary with changes in circuit conditions. In a similar manner, the non-conducting period of the discharge device I2 is stabilized and the frequency of the multivibrator circuit is stabilized. Within reasonable limits, I haveeven found it possible to replace one pair of electric discharge devices H and [2 of a given type and make by another pair of somewhat different type and make without causing variation in the frequency of the multievibrator. circuit.

In the operation as explained, it was assumed that the bias potential E1 was equal to the negative swing E2 of the control electrode. However, the same stability would be obtained if some other fixed ratio were maintained between the value E1 and the value E2, equality of the two values not being necessary. For example, if the switches S1 and S2 are moved to the downward positions, the condensers 35 and 36 will be charged to potentials respectively equalling the peak alternating voltages of the anodes I4 and i3 or one-half the anode voltage swings. Nevertheless, a fixed proportion is maintained between the magnitudes of the voltages E1 and E2, discussed in connection with Fig. 3, and stability of oscillation is obtained. If desired, the circuit may be modified to maintain'any other convenient ratio between the bias potential of each discharge device and the voltage swing of the anode of the other discharge device. 7

In the arrangement of Fig. 1, with the switches 81 and S2 in the downward positions, the potentials of the condensers '35 and 36 may continuously equal one-half the respective anode voltage swings precisely only if it is assumed that the resistors 33 and 34 are large in relation to the resistors 25 and 26 respectively, and that the grid leak resistors 2| and 22, in turn, are large in relation to the resistors '25 and 26. However, these assumed resistance relationships are not necessary to the satisfactory operation of the circuit. For maximum stability, nevertheless, I prefer to utilize resistance relationships substantially as assumed.

As pointed out, the control electrodes I5 and 16 are provided with positive biases which are equal to a substantially constant fraction of the anode voltage swings ofthe opposite tubes and which compensate for variations in swing which may be produced by variations in the voltage of the supply source 29, variations in the load impedances 25 and 26, or variations in tube characteristics. Each tube stage forms a portion of a control circuit for the other so that I may stabilize each stage by compensating variation in the other.

In place of using separate rectifiers for supplying the bias voltages, I may modify the circuits of the main tubes l I and [2 so that each will provide a bias voltage for the control electrode of the other tube. For example, as illustrated in Fig. 2, the tubes II and I2 are provided with cathode resistors 39 and 40, respectively, connected between the cathodes H and I8, and the negative supply terminal 28. 2| is connected between the control electrode 15 and the cathode l8 of the other tube l2, and likewise, the grid resistor 22 is connected between the control electrode l6 and cathode l'l.

In this case the control electrode of each discharge device is biased to the potential of the cathode of the opopsite discharge device when the latter is conducting. Considering the coupling condenser l9, and referring to Fig. 3, E1 is the voltage across the resistor 40 when the device 12 is conducting. As before, E2 is the anode voltage swing of the device I2. E1 and E2 are both proportional to the anode-cathode current or discharge current of the electric discharge device l2. Assuming constant ratio of the resistances of the elements 26 and 40, the ratio of E1 to E2 remains constant and the oscillator is stable in frequency. Variations in load impedance have some effect, but other changes in circuit conditions do not vary the oscillator frequency.

For improving the wave from the voltages and The grid resistor.

7 currents appearing in the tubes in the circuit of Fig. 2, by-pass condensers 4i and 42 may be connected across the cathode resistors -39 and 40, respectively. I have found that stability is obtained with or without such by-pass condensers.

As many changes could be made in the above construction and many apparently widely diiferent embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A stabilized multivibrator, comprising a pair of electric discharge devices each having an anode, a cathode, and a control electrode, first and second supply terminals for connection to a current source, a pair of load impedances connected between the first supply terminal and the respective anodes, coupling-condensers connected between the anode of one discharge device and thecontrol electrode of the other, grid leak resistors connected between the control electrode of one discharge device and the cathode of the other, and cathode resistors connected between the respective cathodes and the second supply terminal.

2. Apparatus such as set forth in claim 1, having by-pass condensers connected across each of the cathode resistors.

3. A stabilized-multivibrator, comprising a pair of electric discharge devices each having an anode, a cathode, and a control electrode; first and second supply terminals for connection to a current source; a pair of load impedances connected between the first supply terminal and the respective anodes; cross-couplings between the anode of one device and the control electrode of the other; and a variable-voltage bias-supply source connected to each of said control electrodes, each bias-supply source comprising a rectifier coupled to the anode of the opposite discharge device.

4. A stabilized multivibrator comprising first and second electric discharge devices each having a cathode, an anode, and a control electrode; first and second impedances respectively connecting the cathodesof said devices to a junction point; means including third and fourth impedances for supplying the respective anodes of said devices with positive potentials relative to said junction point; fifth and-sixth impedances coupling the control electrode of said first device respectively to-the anode and to the cathode of said second device; and seventh and eighth impedances coupling the control electrode of saidsecond device respectively to the anode and to the cathode of said first device. I

5. A stabilized multivibrator comprising first and second electric discharge devices each having a cathode, an anode, and a control electrode; first and second impedances respectively connecting the cathodes of said devices to a junction point; means including third and fourth trode; first and second impedances respectively connecting the cathodes of said devices to a junction point; means including third and fourth impedances for supplying the respective anodes of said devices with positivepotentials relative to said junction point; fifth-and sixth impedances connected in series between the anode and cathode of said first device, the junction thereof being coupled to the control electrode of said second device; and seventh and eighth impedances connected in series between the anode and cathode of said second device, the junction thereof being coupled to the control electrode of said first device.

'7. A stabilized oscillation generator of the multivibrator type for producing a signal having a given period, comprising a pair of electric discharge devices each having an anode, a cathode and a control electrode; first and second supply terminals for connection to a current source; a pair of load impedances connected between the first supply terminal and the respective anodes; cross-couplings between theanode of each device and the control electrode of the other, said cross-couplings having time constants short relative to said period; a direct-current bias-producing means associated with each of said devices for providing a voltage dependent upon the average amplitude of anode voltage and current variations in the device but substantially independent of cylical variations thereof; and electrically conductive impedance means connecting the direct-current bias-providing means associated with each device to the control electrode of theother device.-

8. A stabilized oscillation generator of the multivibrator type \for producing a signal having a given period, comprising first and second electric discharge devices each having a cathode, an anode and a control electrode; first and second supply terminals for connection to a current source; a pair of load impedances connected between the first supply terminal and the re-' spective anodes; a cross-coupling between the anode of the first device and the control electrode of the second device and a cross-coupling between the anode of the second device and the control electrode of the first device, said crosscouplings having time constants short relative to said period; direct-voltage storage means connected to the first device-for producing a direct voltage dependent on the average amplitude of current variations insaid first device but'substantially independent of cyclical variations thereof electrically conductive impedance means coupling said storage means to the control electrodeof said second device; further direct-voltage storage means connected to the second device for producing a direct voltage dependent on the average amplitude of current variations in said second device but substantially independent of cyclical variations thereof; and further electrically conductive impedance means coupling said further storage means to the control electrode of said first device.

9. A stabilized multivibrator comprising first and second electric discharge devices each havinga cathode, an" anode, and a control electrode; a pair of load imp'edanc'e's' connected respectively between said anodes and the positive terminal of a source of potential; means for applyig to each of saidcontrol electrodes a-unid'irectional potential having a magnitude dependent upon the average amplitude' oi the current flowing in the circuit or theopposite anode; and separate means for applying to each of said control elee- Number trodes a potential dependent upon the voltage 2,157,533

fluctuations at the opposite anode. 2,254,852 DAVID E. KENYON. 2,282,895

5 2,302,690 REFERENCES CITED The following references are of record in the 2,154,492 Clough Apr. 19, 1939 Name Date Geiger May 9, 1939 Miller Sept 2, 1941 Shepard May 12, 1942 Germeshausen Nov. 24, 1942 FOREIGN PATENTS Country Date Great Britain Nov. 8, 1937 OTHER REFERENCES Transactions AIEE, vol. 60, 1941, pp. 371-376, (Copy in Div. 51.)

Certificate of Correction Patent No. 2,441,579. May 18, 1948.

DAVID E. KENYON It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows: Column 5, line 3, for curve 27 read curve 87; column 6, line 61, for opopsite read opposite; line 75, for the word from read form of; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Ofiice Signed and sealed this 27th day of July, A. D. 1948.

THOMAS F. MURPHY,

Assistant Oommiaaz'oner of Patents,

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