US2392114A - Pulse system - Google Patents

Description

Jan. 1, 1946. E. H. B. BARTELINK 2,392,114

PULSE SYSTEM Filed Jan. 23', 1943 2 Sheets-Sheet 2 Fig. 4.

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OUTPUT SOURCE OF SIGNA L POTENTIA L5 inventor t Everhard H.B.Bartelink,

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His A1311 orrwegi Patented Jan. I, 1946 PULSE SYSTEM E verhard n. B. Bartelink, West Milton, N. Y., as-

signorto General Electric Company, a corporation of New York Application January 23, 1943, Serial No. 473,360

9 Claims.

My invention relates to pulse systems and more particularly to pulse generating, synchronizing and mixing systems.

More particularly my invention relates to pulse systems employing multivibrators and it has for its object to provide certain improvements in such multivibrators with respect to the operation thereof, the character of pulses derived therefrom and to the means of coupling thereof to desired load circuits.

My present application is a continuation in part of my parent application Serial No. 342,321, filed June 25, 1940, now Patent No. 2,338,395, issued January 4, 194 entitled Signal transmission systems, and which is assigned to the assignee of this present application. In that application I have dealt at length with multivibrators of the type in which a positive bias voltage is supplied to the control electrodes of the discharge devices involved and in this application I shall describe and illustrate such multivibrators. It will be understood, however, that my present invention is not limited to multivibrators of the positive bias type but is generally applicable to multivibrators.

An object of my invention is to increase the stability of the frequency of multivibrators during variations in the characteristics of the discharge devices employed, as due to aging or other factors affecting the gain of such discharge de-- vices.

A. further objeot oi my invention is to effect such increase in stabilization by degeneration.

Still another object of my invention is to secure such degeneration through means which facilitates coupling between multivibrators, aids in securing square wave form of pulses produced, and avoids any considerable increase in complexity or cost of the apparatus.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with. the accompanying drawings in which Fig. 1 represents an embodiment of my invention; Figs. 2a to 2d represent the character of pulses produced in the multivibrators of Fig. 1; Figs. 3a to 3h represent certain further characteristics of the operation of the equipment of Fig. l; and Fig. 4 represents a further embodiment of my invention.

Referring to Fig. i. of the drawings, I have shown therein a pair of multivibrators I and 2 connected in cascade between a signal source 20.

and a load device which may be connected between the output terminals 28.

The multivibrator I comprises a pair of electron discharge devices 3 and 4, each comprising an anode, a cathode and a control electrode. The anodes of these two devices 3 and 4 are connected through respective individual resistances 5 and 6 and through a further common decoupling resistance 1 to the positive terminal of a source of operating potential which may be connected between conductors 8 and 9, the latter of which is grounded as at ill. Each of the cathodes of these devices 3 and t is also connected to ground through individual resistances II and I2, respectively. The anode of each device is connected to the control electrode of the opposite device through the usual condensers I3 and I4, and each control electrode is connected through the usual grid resistances l5 and IE to the cathodes. In the multivibrator I, this latter connection is made through the resistance ll, common to the control electrodes, to a variable contact l8, which is variable along resistance 19, which is connected between conductors 8 and 9 and hence in shunt with the source of anode operating potential. this way the two control electrodes are biased positively with respect to their cathodes to an extent which may be varied to vary the frequency of the pulses produced by the multivibrator.

It will be observed that each of the resistances ii and i2 is connected both in the anode cathode circuit and the control electrode cathode circuit of the respective discharge device. Thus any potential produced on these resistances by reason of current flow in the anode circuit is supplied back to the control electrode of the respective discharge device in degenerative phase. It has been found that these resistors, producing degeneration as thus described, materially improve the stability of the frequency of pulses produced by the multivibrator during variations in the characteristics of the discharge devices 3 and 4, as due to aging or due to the other factors which affect the gain of such discharge devices. It can readily be shown, both mathematically and experimentally, that the frequency of such pulses is dependent upon the gain in the two discharge devices. In accord with my invention variations affecting such gain may, to a very substantial extent, be prevented from afiecting the frequency of the pulses by the use of the cathode resistors H and i2 as previously described.

In addition, these resistors serve as convenient coupling means between successive multivibrators and aid materially in the production of square wave pulses by the use of such multivibrators. This operation will become apparent as this description proceeds. These resistances may, desirably, be of the order of one thousand ohms in a system in which resistances 5 and 6 are of the order of five thousand ohms. Resistances I5 and I6 may be varied in accord with the relative duration of the successive pulses of the system and may be respectively one-tenth and one-half of a megohm.

The pulses produced bythe multivibrator I may be synchronized with, or otherwise controlled by, a source of signal potentials 20, which may be a further source of pulses, which is connected across the resistance II through a suitable decoupling resistance 23. The pulse voltages which appear upon the resistance I2 may be supplied across the resistance II' of the multivibrator 2 to synchronize the pulses generated in the multivibrator 2. This latter multivibrator may be of the same type as that previously described but which may operate at a different frequency, such as a frequency which is either a harmonic, or a sub-harmonic, of the frequency of the pulses produced by themultivibrator I. The connection between the cathode bias resistors I2 and II is suitably effected by means of a unilateral conducting device 25, such as a diode, or copper oxide rectifier, and a resistance 26, the unilateral conf ducting device 25 having its anode connected to a variable tap 21 on resistance I2 and its cathode connected through resistance 26 to the cathode of the discharge device 3 of the multivibrator 2. In this way, when the contact 21 is positive with respect to the cathode of the discharge device 3, as when a current pulse exists in resistance I2, current flows through the unilateral device 25 to the resistance II' and triggers the multivibrator 2; In this way the multivibrator 2 is maintained in synchronism with the multivibrator I. A current pulse, however, produced by multivibrator 2 in resistance II' renders the cathode of unilateral device 25 positive with respect to its anode and thus no current flows in this device 25. In this way the multivibrator I synchronizes the multivibrator 2 but is not affected by the operation of multivibrator 2.

Pulses produced in resistance I2 of multivibrator 2 maybe supplied to an output circuit 28 through an electron discharge device 29 in which they may, if desired, be mixed with further pulses supplied from an input circuit 36. The cathode of the discharge device 29 is connected directly to the cathode of the discharge device 4' in multivibrator 2 and thecontrol electrode of device 29 may be connected directly to ground, although, as shown in Fig. 1, this connection is efiected by closing a switch 34. This switch may be shunted by a resistance 35 across which, when the switch is open, pulses may be supplied from the circuit 30.

The operation of the apparatus as thus described may best be understood by reference to Figs. 2a to 2d and Figs. 3a to 3h. Referring first to Fig. 2a, the curve 36 represents the variation in anode voltage on discharge device 3 with time, the dotted line 31 corresponding to zero voltage and the dotted line 38 corresponding to the unidirectional voltage which exists across condenser 40, as shown in Fig. 1, this condenser 40 comprising the usual large capacitor commonly employed in decoupling such systems from the power supply Source. Of course, since current flows from the anode source through the two discharge devices alternately, a continuous current flows from the anode source through resistance I and the potential on condenser 40 assumes a constant average value less than that of the source.

As seen from curve 36 the anode voltage on device 3 rises in sharp, regularly recurring positive pulses and then drops to a lower value at the ends of these positive pulses.

The curve 44 of Fig. 2b represents the varitions in anode voltage on device 4 of Fig. 1. This anode voltage drops as the anode voltage 0! device 3 rises and rises as that on device 3 drops.

Figs. 2c and- 2d represent by curves 45 and 46 the voltage on the cathodes of devices 3 and 4, respectively.

To describe the cycle of operations, let us start with the time indicated at A in Figs. 2a and 2b when the anode voltage on device 3 is high and that on device 4 is low. Condenser I4 has such a charge that the control electrode of device 3 is suiiiciently negative to prevent flow of current in this device, and this condenser is discharging through resistances 6, 1, l9, I1 and I5, the discharge being aided by the voltage on resistance I3.

When the charge on condenser I4 is sufliciently reduced that the cutofi point of device 3 is reached, current begins to flow in that device producing a voltage drop on resistance 5. Since condenser I3 is charged, this change in voltage drives the grid of device 4 in the negative diretcion reducing current in that device. The anode voltage of device 4 thus rises, this change in voltage being transferred to the grid of device 3 by condenser I4 and aids the original deviation, this regenerative action continuing until anode current in device 4 is completely interrupted.

During this regeneration period, sometimes refered to as flip-over" period, the grid of device 3 is driven positive by the voltage on condenser I4. This voltage rapidly leaks oil? through the circuit comprising resistance 6, grid to cathode space of device 3, which has low resistance when the grid is positive, and resistances I I and 1, this circuit having a time constant that is small relative to the period of the multivibrator cycle. The current flowing in the anode of device 3 when the grid is momentarily positive produces the voltage variation indicated by the curved portion 48 of curve 36 of Fig. 2a. The discharge current through resistance 6 produces a drop thereon which prevents the anode voltage on device 4 from rising immediately to its maximum value. Instead it rises according to the exponential portion 50 of the curve 44. Since this discharge current flows through resistance II, it produces the exponential portion 55 of curve 45 of Fig. 20.

During this regenerative period, the drop in voltage on resistance 5 is applied in full, through condenser I3, to the control electrode of device 4 driving it negative beyond cutoff and completely interrupting current in this device. Thus the current in resistance l2 drops immediately to zero as shown at 51 in Fig. 2d.

This condition now remains until the charge on condenser I3 leaks off through the path including resistances 5, 1, I3, I1 and I6 to such a point that device 4 again passes current. The regenerative action then recurs and the devices are returned to the starting condition, the grid of device 4 becoming positive momentarily during rapid discharge of condenser I3 through its grid to cathode space and producing the anode voltage variation indicated by the portion 43.01 curve flows in resistance producing the exponential portion 41' of the curve 36 ofFigL 2a.; This discharge current also flows in resistance I 2 producing the exponential portion 56 of' the curve 46 of Fig. 2d. However, since the grid of device 3 is driven negative, the current in device 3 and resistance I l is interrupted immediately.

Thus the voltage variations on the anodes o devices-3 and I are exponential at each limit of variation as shown by the curved portions 41 and 48 of curve 36 and by the curved portions 49 and 50 of the curve 44. Thus to convert the voltage variations represented by curves 36 and 44 to square pulses requires two clipping, or limitingoperations usually requiring at least two discharge devices. To convert the wave 36, for example, to a square pulse wave it is necessary to transmit it through a device incapable of passing voltages greater than the value represented by the line 5| in Fig. 2a. Itis also necessary to supply it through a device which produces no output current except when the applied voltage is greater than the value .represented by the line 54 of Fig. 2a.

A similar operation is necessary to convert the pulses represented by the curve 44 to square wave form.

It will be observed, however, that the curves of Figs. 2c and 2d are both square at the lower limit of the voltage variation, the only curvature being at the points 55 in the curve 45 and 56 in the curve 46. Thus to convert the pulses of Fig. or 2d to square pulses but one clipping operation is required. For example, if the pulses of Fig. 2c be supplied through a device incapable of passing voltage variations greater than that represented by the dotted line 50, the output of such device would comprise a square wave. The same clipping operation may be eflected with the pulses of Fig. 211 to produce a square wave.

In Fig. 1 the device 29-converts the wave 46, which appears on the cathode resistor l2 to a square wave between the output conductors 28. Thus, for example, during any current pulse in device 4' the potential on resistance, I2 is suificiently great to drive the cathode of device 29 sufficiently positive with respect to its control electrode to render that device nonconducting. Thus the square wave appears between the anode and ground and may be supplied to the output circuit 28 through condenser 63.

This latter operation is illustrated in Fig. 3. Fig. 3a represents pulses similar tothose represented in Fig. 2d. Since these pulses drive the cathodes positive, they appear as negative pulses as between the control electrode and cathode and may be represented as shown in Fig. 3b. The resulting square pulses, which appear between the anode and cathode, or between the output conductors 28, are illustrated in Fig. 3c. Of course, it is assumed that the switch 34 is closed. If this switch be opened and additional pulses be supplied between the control electrode of device 29 and ground as from the input circuit 30, then these pulses may be mixed with such additional pulses. For example, let us assume that the pulses supplied from the circuit are as represented in Fig. 3d. These pulses are added to the pulses which appear on resistance I2 to produce a voltage between the control electrode and cathode which may be represented by the curve of Fig. 3e. Since the discharge device is rendered nonconducting by the pulses on resistance l2, the anode voltage of device 29 is as indicated by the curve of Fig. 3! in which the pulses from the input circuit 30 appear during the intervals between pulses from resistance l2 and are interrupted during such latter pulses. If desired, by proper propor tioning of resistance 55 both of these sets of pulses may be reproduced on the anode in the form represented by Fig. 3h; x

The multivibrator 2 of Fi l differs from the multivibrator I thereof in that the control electrode of the discharge device 4' is connected through its resistance l6 and a filter resistance l0 to an intermediate point on resistance 14 connected between ground and a variable contact 15 on bleeder resistance 18, which is connected between the conductors 8 and 9. The control electrode of discharge device 3' is connected through its resistance i5 and filter resistance 11 to a variable tap on resistance 18 connected between ground and the variable tap 15. By variation of the tap l5 the positive bias applied to the control electrodes of the two discharge devices may be varied in unison thereby to vary the frequency of pulsations produced without affecting the pulse width in either device. By variation of the tap 19 on resistance 18 the bias voltage on discharge device 3 may be varied without varying that on the control electrode of discharge device 4'. This is desirable in adjustment of the relative duration of the pulses passed by the two discharge devices. These two controls are effected in a part of the circuit in which no alternating potentials exist, being effected solely by variation of. unidirectional bias potential.

The advantage of the positive bias as applied to' electrodes of a multivibrator has been explained in my above referred to parent application. By variation of the positive bias the frequency, with the same set of circuit constants, may be varied over a range of substantially 6 to l, a linear relationship existing between the bias and irequency throughout the range. Also the pulse width remains constant throughout substantially the entire range but varies to some ex tent in the region of lower bias. Th positive bias likewise materially reduces the efiect of extraneous electromotive forces which may be induced undesirably into the system from extraneous sources, upon the duration of the pulses or the frequency thereof. The reasons for this effect have been clearly set forth at some length in my above referred to parent application, and lie essentially in the fact that. during operation of the multivibrator, the voltage variation on either control electrode with respect to time, in the region of anode current cut off, is more rapid the higher the positive bias. Thus the time inter val during which any extraneous undesired voltage of given intensity may trigger either device from the nonconducting state to the conducting state is reduced by increased .positive bias.

The efiect of such extraneous influences is additionally reduced by the use of the cathode bias resistors ll, l2; ll, l2, in that they permit the use of low impedance coupling circuits between the multivibrators, or from either multivibrator to a pulse source, or to a load, and thus reduce the likelihood of either multivibrator being aflected by extraneous influences affecting such coupling circuits. These cathode resistors also obviate the need for potentiometer-s for voltage reduction in such circuits, and, being of low impedance, apparatus for monitoring the operation of either multivibrator, either as to frequency or intensity of pulses produced, may be connected across such resistors without afiecting the operation of the respective multivibrator.

Fig. 4 shows a form of my invention in which the multivibrator comprising discharge devices 3" and 4" is arranged to have its grid bias varied in accordance with a signal potential, and in which degeneration is advantageously employed to maintain constant average pulse frequency. The two control electrodes of these discharge devices are connected through their respective resistors l5 and 16 to a common lead 1! connected to the anode of a discharge device 80. This latter discharge device has its cathode connected to ground and to the negative terminal of the source of operating potential, and its anode connected to the positive terminal of the source of operating potential through a resistance 84. It is shown as having a source of signal potential connected between this control electrode and cathode through the usual coupling condenser 86. This control electrode is connected to the cathode through the usual grid resistance 85. This source of signal potential may comprise a microphone or an audio amplifier through which electromotive forces representing the voice or music are supplied between the control electrode and cathode of the device 80. The impedance between the cathode and anode of this device varies in accordance with these potentials thereby varying the anode potential of 80 which is equivalent to changing the potential between the control electrodes and cathodes of the two devices 3" and 4" of the multivibrator. This in turn varies the frequency of the pulses produced by the multivibrator in accord with the voice potentials. These pulses are supplied through a suitabl filter 81 to the control electrode of an electron discharge device 88. The filter removes all harmonics of the fundamental frequency produced by the multivibrator leaving only a sine wave of voltage of the fundamental frequency which is modulated in frequency in accord with the voice or music. This frequency modulated fundamental is supplied to the control electrode 94 of device 88.

This device 88 has a plurality of electrodes spaced successively between the cathode and anode. The two electrodes nearest the cathode are connected to opposite terminals of an oscillatory circuit 89 the intermediate point of which is connected through a resistance 9|] to the positive terminal of the source of operating ,potentiai. These electrodes are shielded from th input electrode 94 by the screen electrode 95 and this input electrode 94 is shielded from the anode by the screen electrode 96, the anode being connected to the positive terminal of the source of operating potential through resistance 91.

Inoperation, oscillations are generated in the circuit 89 of desired frequency and modulate the electron stream flowing from the cathode to the anode as do the frequency modulated oscillations supplied to the control electrode 94. In the anode circuit oscillations having the sum and the difference of the frequencies of the oscillations generated in circuit 89 and those supplied to electrode 94 appear, these oscillations being modulated in frequency in accord with the voice or music.

The frequency of th multivibrator of Fig. 4 may be varied in accord with the voice or music potentials over a very large percentage of the average frequency, as, for example, forty per. cent, linearly and without distortion. This range may be increased to about seventy-five percent if the multivibrator be constructed symmetrically, that is with its constants so proportioned that each discharge device passes current half of the time. This operation eliminates even harmonics in the output and the filter is thus required to eliminate only the odd harmonics. By use of cathode resistors II" and I2", and the degeneration previously referred to, this average frequency may be stabilized against variables affecting the gain 01 the discharge devices, such as deterioration with age, and thus this average frequency may be maintained substantially constant. Of course, the frequency with which this frequency is heterodyned is constant and may, if desired, be

crystal controlled thereby resulting in a highly stable resultant frequency which may be either higher or lower than the average frequency of the multivibrator and which appears between output conductors 89.

While I have shown particular forms of my invention, it will, of course, be understood that I do not wish to be limited thereto since various modifications in the circuit arrangements and in the instrumentalities employed may be made, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure Letters Patent of th United States is:

1. A transmission system comprising a multivibrator including a plurality of electron discharge devices each having an anode and control electrode, circuit means responsive to change in current in each device to produce opposite change in current in the other devic and to render each of said devices alternately conducting and nonconducting, means connected to each of said discharge devices responsive to current therein to supply voltage to the control electrode of the same device to produce negative feedback therethrough, input and output circuits, and means including said multivibrator to interconnect said circuits.

2. In combination, a multivibrator comprising a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having its negative terminal connected to both of said cathodes through individual resistances and its positive terminal connected to both of said anodes through individual resistances, and the anode of each device being capacitively coupled to the control electrode of the other device whereby pulses of current are cyclically produced in each of said devices and said first mentioned individual resistances having value sufliciently great materially to reduce variation in the frequency of said pulses produced by changes in the gain of either of said discharge devices.

3. In combination, a multivibrator comprising a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having its negative terminal connected to both of said cathodes through individual resistances and its positive terminal connected to both of said anodes through individual resistances, and the anode of each device being capacitively coupled to the control electrode of the other device whereby pulses of current are cyclically produced in each of said devices and said first mentioned individual resistances having value sufilciently great to stabilize the frequency of said pulses against changes in the gain of either of said discharge devices and said current pulses in said first mentioned individualresistances producing voltage variations thereon of square wave form at one limit of said variations.

4. In combination, a multivibrator comprising a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having its negative terminal connected to both of said cathodes through individual resistances and its positive terminal connected to both of said anodes through individual resistances, and the anode of each device being capacitively coupled to the control electrode of the other device whereby pulses of current are cyclically produced in each of said devices and said current pulses in said first mentioned individual resistances producing voltage variations thereon of square wave form at one limit of said variation, a limiter connected to one of said first mentioned resistances having an output circuit and including means to produce pulses square at both limits of variation in said output circuit.

5. In combination, a multivibrator comprisng a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having its negative terminal connected to both of said cathodes through individual resistances and its positive terminal connected to both of said anodes through individual resistances, and the anode of each device being capacitively coupled to the control electrode of the other device whereby pulses of current are cyclically produced in each of said devices, an additional electron discharge device having an anode, a cathode, and a control electrode, said cathode being connected to one of said first mentioned cathodes and through the respective individual resistance to said last mentioned control electrode, the voltage variation on said respective individual resistance being greater than that required to reduce the current in said third device to zero, and a square wave utilization device connected to the output of said third device.

6. In combination, a plurality of multivibrators, each comprising a pair of electron discharge devices and a source of operating potential, said discharge devices each comprising an anode, a cathode, and a control electrode, said source of operating potential having a negative terminal connected to both cathodes of the respective multivibrator through individual cathode resistances and having a positive terminal connected to both anodes of the respective multivibrator through individual resistances, and each anode in each multivibrator being connected through a respective condenser to the control electrode of the other discharge device in the respective multivibrator, whereby each multivibrator generates recurrent voltage pulses on said cathode resistances, and a coupling between aid multivihrators comprising a unilateral conducting device connected between a cathode resistance of one of said multivibrators and a cathode resistance in the other of said multivibrators, thereby to transmit pulses from one of said multivibrators to the other and to prevent pulses generated in said other multivibrator from affecting said one multivibrator.

'7. In combination, a multivibrator comprising a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having a negative terminal connected to said cathodes through individual cathode resistances and having a positiv terminal connected to said anodes through individual anode resistances, and individual capacitances connected between each anode and the control electrode of the other of ,said discharge devices whereby said multivibrator generates voltage pulse variations of square wave form at one voltage limit of the pulse on each cathode resistor, means to supply synchronizing pulses to on of said cathode resistances to synchronize said multivibrator and a limiter connected to receive pulses from theother cathode resistance and to limit said pulses to square wave form at the other voltage limit of said pulses whereby pulses square at both limits appear in the output of said limiter.

8. In combination, a pair of electron discharge devices, each having an anode and 'a cathode, a source of anode operating potential having a negative terminal connected to the cathodes of both of said devices through a common resistance and a positive terminal connected to the anode of one of said devices, means comprising the other of said devices to generate current pulses in said common resistance, a source of voltage pulses, a control electrode for said one device connected through said source and said common resistance to said cathodes, the current pulses in said common resistance being sufllciently intense to prevent current flow in said one device during said current pulses whereby current flows in said one device only during in-- tervals between said current pulses and is then controlled by pulses from said source.

9. In combination, a multivibrator comprising a pair of electron discharge devices, each comprising an anode, a cathode, and a control electrode, a source of operating potential having its negative terminal connected to both of said cathodes through individual resistances and its positive terminal connected to both of said anodes through individual resistances, and the anode of each device being capacitively coupled to the control electrode of the other device whereby pulses of current are cyclically'produced in each of said devices, means to vary the frequency of said pulses over a wide range in accord with a signal potential, said first mentioned individual resistances having value sumciently great materially to stabilize the average frequency or said pulses against dritt during changes in the gain of either of said devices.

EVERHARD H. B. BAR'I'ELINK.

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