US2526551A - Delayed-action pulse repeater - Google Patents

Description

92 mN W JITNM S Q Q Q Q N Allll m bN N m T T A INVENTOR A. S. GANO d Patented Oct 11, 1950 UNITED sTATEs PATENT OFFICE .DELAY-ED ACTION PULSE REPEATER Alfred S. Gano, White Plains, N. Y., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application April 20, 1946, Serial No. 663,688

4 Claims.

This invention relates to a repeating device for electrical pulses and more particularly to a delayed .action repeater, that is, one in which an impressed input pulse gives rise to an output pulse after a predetermined delay interval.

An object of the invention is tomake the length of the delay. interval'substantially independent of the repetition rate of the pulses to be repeated, even at repetition rates as high as 80,000 or moreper second.

Another object is to make the length of the delay interval readily adjustable over a range of values from a quarter of the repetition period to three-quarters of that period, more or less.

Afurther object of the invention is to improve the operation of a multivibrator as a delayed action pulse repeater.

A feature of the invention is the use of a rectifying element in the grid circuit nfone section of a multivibrator. Y

Another feature is the use of a variableanode loadresistor in a delay multivibratorto vary the amount of the delay. 7

These and other objects and features of the invention are explained in more detail in the following description and illustrated in the accompanying drawing, the single figure of which is a schematic representation of a pulse gener- 'ating and repeating system embodying' the invention. V V

The drawing shows a system comprising-a piezoelectric crystal um't ill and a plurality of vacuum tubes II to "[5, inclusive. The vacuum tubesare all shown as 'triodes butmore elaborate tubes having additional electrodes may be substituted for the triodes if desired.

The "unit ill-comprises a conventional'cornbination of a" piezoelectric crystal, supporting means therefor, and a paifof electrodesfbetween which the, crystal is supported. The vacuum tube II together with the-unit l and'interconnections constitute a conventional type of piezoelectrically controlled oscillation generator. The tubeiZ with associated'circuit elements constitutes a pulse generator of the type commonly known as a blocking oscillator and is arranged to be controlled'in conventional manner, that is, synchronized'by the output of the tube H. The tubes I3 and M with their associated circuits constitute a delay multivibrator which while to some extent conventional in'circuit continuity, has a unique mode'of operation as willbe described in detail hereinafter.

The multivibrator is controlled by the blocking oscillator through a rectifying element 16 in accordance with this vibrator is controlled by means of a variable resistor I! in the anode circuit of the tube 13,

also in accordance with this invention. The output of the multivibrator is impressed upon the grid circuit of the tube l5, which tube is intended to be representative of any suitable utilization circuit for the delayed pulses from the multivibrator.

The blocking oscillator tube l2 has a cathode l8, a control grid [9 and an anode 20. A transformer is provided having three windings, wind- The cathode I8 is connected to groundthrough invention and the delay interval of the multia cathode resistor 29.

Coupling is provided between the blocking oscillator l2 and the grid of the tube l3 in the multivibrator through the rectifying element IB and a resistor 30. The grid of the tube l3, designated 3|, is connected to ground through a resistor 32. The tube l3 has a cathode 33 and an anode 34. The tube I4 has a cathode 35, a grid '36 "and an anode 31. i The internal connections of the multivibrator include a capacitor 38 connected between the anode of the tube [3 and the grid of the tube I4. The anode 34 is connected to .the positive terminal'of the battery Zfil'through the variable resistor ll and a fixed resistor 39. The anode 31 of the tube [4 is connected to the positive terminal of the battery 24 through a pair of fixed resistors 40 and 4| across the resistor 4| of which there is connected the primary winding of an output transformer 42, the secondary windingof which is connected between the grid and cathode .of the tube l5. The grid 36 of the tube I4 is connected to the positive terminal of the battery 24 through a resistor 43 of relatively large resistance value. The cathodes 33 and 35 are connected together and jointly grounded through a cathode resistor 44. A

capacitance 45 is shown in dotted lines connecte ingthe grid 36 and cathode 35 of the tube M.

The capacitance 45 represents the effective interelectrode capacitance of the grid-cathode circuit of the tube l4 under operating conditions.

A coupling condenser 46 is shown connected to the junction point of the resistors 25 and 26 in the anode circuit of the blocking oscillator l2 for the purpose of taking off a supplementary output from the blocking oscillator for utilization elsewhere.

The multivibrator is represented as having a pair of input terminals 41 and 48, the former having the rectifying element I6 connected in series therewith and the latter being grounded.

In the operation of the system illustrated, the tube 2 l is energized by the battery 24 to produce oscillations which energize the crystal which in turn exerts a control over the oscillations of the tube H and tends to stabilize the frequency of the oscillation in known manner. The oscillations are fed through the winding 2| and are effective therein to synchronize the operation of the blocking oscillator I2 with the oscillator II and crystal unit In, also in known manner. The pulses generated by the blocking oscillator I2 appear in the winding 2i and are transmitted through the resistor 30, the input terminal 41, the

rectifying element l6 and the resistor 32 to ground. The potential drop produced in the resistor 32 by the current of the pulse from. the blocking oscillator is eifective to apply a positive pulse to the grid 3| of the tube l3 thereby triggering the multivibrator.

In the absence of a triggering pulse, the multivibrator comprising the tubes l3 and [4 assumes a stable condition consistent with the connection of the grid 36 of the tube I4 to the positive terminal of the battery 24 through the resistor 43. This connection places a high initial positive potential upon the grid 36, making the tube I4 normally highly conductive, passing anode and grid currents through the common cathode resistor 44. The voltage drop in the resistor 44 impresses a large negative potential upon the grid 3| of the tube [3 thereby rendering the tube l3 normally non-conductive. While this stable condition of the circuit is being established, the capacitor 38 is charged through the resistors 11, 39 and to a potential substantially equal to the full battery potential less the potential drop maintained in l the resistor 44 by the combined anode and grid currents of the tube Hi, the negative side of the capacitor 38 being at the grid 36.

When a sufficient positive potential is superposed upon the grid 3l, as by means of a pulse through the resistor 32, the tube 13 is rendered conductive, thereb lowering the potential of the anode 34 and with it the potentialof the grid 36 due to the charge on the capacitor 38. The lowering of the potential of the grid 36 reduces or preferably cuts off the current through the tube M. This action in turn reduces the potential drop across the resistor 44 and enables the tube E3 to continue in the conductive condition even after the cessation of the positive pulse in the resistor 32. The circuit remains in this new condition with the tube l3 conductive and the tube 14 non-conductive, until the charge on the capacitor 38 has been reduced sufiiciently to enable the tube M to become conductive once more. When conduction begins again in the tube [4 a potential difference is generated across the resistor 4| which is transmitted through the transformer 42 to the tube l as a delayed pulse.

I During the portion of the cycle when the tube 13 is conductive, the capacitor 38 is efi'ectively connected between the battery terminals in series with the resistor 43, the anode-cathode path of the tube l3, and the resistor 44. The polarity of this connection is such that the capacitor 38 tends 4. to discharge and then to recharge in the opposite direction toward the full battery potential. However, the cut-off potential of the tube I4 is reached upon the grid 36 at about the same time as the initial discharge is completed. @The time constant of the circuit, for the values given, namely micromicrofarads in capacitor 38 and one megohm in resistor 43, neglecting resistor 44, is 100 microseconds. The discharge time until the cut-01f potential is reached is only a fraction of 100 microseconds and depends upon the initial potential at the grid 36. The initial grid potential in turn depends upon a number of factors. Certain of the latter arise from the fact that in practice the tube l3 does not constitute a perfect short-circuit from its anode to its cathode when in the conductive condition. Accordingly, the anode 34 does not drop to the potential of the cathode 33. The valueto which the anode potential falls depends upon the relative resistance values of the resistors I1, 39, 44 and the anodecathode path of the tube l3 in the operating condition. The value of the anode potential together with the potential difference between the anode ,34 and cathode 33 determines the initial value of the potential of thegrid 36 relative to the cathode 35, as it will be evident that the gridcathode potential difference in the tube i4 is the algebraic summation of the anode-cathode potential difference in the tube l3 and the potential difference between the terminals of the capacitor 38.

Another factor aifecting the initial grid potential is the sharing of charge between the capacitor 38 and the interelectrode capacitance 45. During the portion of the cyclein which the capacitor 38 is being charged through the resistors I1, 39 and 44, the interelectrode capacitance 45 is substantially 'short-circuited by the grid-cathode path of the tube l4. However, when the triggering pulse is impressed upon the grid 3| of the tube l3 and the tube 14 is consequently rendered non-conductive, the charge on the capacitor 38 is shared with the capacitance 45 by means of current flowing through the anode-cathode path of the tube 13. The resultant grid-cathode potential is less than the initial potential difference in the capacitor 38 and its amount is further lessened by the presence of the anodecathode potential difierence in the tube I3. In an embodiment which was built and-successfully operated, the capacitance 45 amounted effectively to 30 to 40 micromicrofarads. The time required for the grid 36 to reach cut-off was, found to range from a minimum of about 3 microseconds toa maximum of about 8 microseconds, depending upon the setting of the variable resistor I 1 in the anode circuit of the tube l3. By means of the variable resistor I! theinitial potential of the grid 36 was adjustable over a range from 90 to volts, more or less. The system was found to be operable at pulse repetition rates as high as 80,000 cycles per second, which rate corresponds to a cyclic period of 12 microseconds. Each impressed input pulse gives rise to an output pulse after an interval which may be adjusted, as for example, within the limits from 3 to 8 microseconds, more or less. Other repetition rates may of course be employed as desired and the time delay interval may be adjusted to a desired portion of the cyclic time, at least within wide limits.

Many conventional multivibrators have a coupling condenser or other coupling impedance ele- .ment with one terminal connected to the anode of the first tube and other terminal to the grid of thesec'ond tube and have another coupling condenser o'r coupling impedance element similarly connected between the anode of the second tube and the grid of the first tube. It has been customary in impressing a triggering pulse upon a multivibrator of this type to insert a unidirectional'conductor or rectifier between the triggering source and the grid of one tube in the multivibrator. The rectifier was arranged to conduct only in the direction required to pass the triggering pulse. The presence of the rectifier served to reduce or prevent reaction of the multivibrator upon the triggering source.

In the type of multivibrator circuit disclosed herein, the coupling between the anode 31 and the grid 3! is accomplished by means of the cathode resistor 44. Accordingly, a change in anode current in the tube I4, while it affects the potential difference between the grid 3| and the oathode 33 by producing a potential drop in the resistor M, does not affect the potential difference between the grid 3! and ground. Hence it would seem feasible to connect a triggering source between the grid 3! and ground, with or without a rectifier, as desired, and without incurring a reaction of the multivibrator upon the triggering source. In other words, the triggering source is decoupled with respect to the coupling means which couples the anode 31 to the grid 3!. Experience with multivibrators of this type at moderate repetition rates has confirmed this conclusion.

At the frequencies and repetition rates here contemplated, namely 80,000 cycles per second or more, however, the circuit was found not to work satisfactorily without a rectifier between the triggering source and the grid 3|. Applicant discovered that an unexpected improvement in operation was obtainable by the use of the rectifier as specified.

'6 winding of relatively low directecurrent resistance between the grid andcathode of said first space discharge device constituting a grid leak path of excessively low impedance, and a substantially unidirectional conductor in series connection in series with said excessively low impedance grid leak path and having its direction of conductivity in the direction of flowof the impressed control im'pulse, thereby blocking reverse current grid leakage through said path of excessively low impedance.

2. A multivibrator comprising two space di'scharge devices each having an anode, a cathode and a grid, said cathodes being connected to a common cathode terminal, a capacitor connected between the anode of the first said space discharge device and the grid of the second said space discharge device, a feedback resistor connected in a circuit between said common cathode terminal and the grid of the first space discharge device, a grid leak resistor serially connected between the grid of the first space discharge device and the said feedback resistor, a source of unidirectional control impulses, connections from said source to the respective terminals of said grid leak resistor, said last-mentioned connections together with said control impulse source being of relatively low impedance compared with said grid leak resistor, and a substantially unidirectional conductor in series connection with said control The element 16 between the input terminal 41 to act to give a higher impedance looking back.

toward the input from the grid of the tube'l3 It has been found that with the rectifying element in the circuit as shown, therange of delay variation which may be obtained is greater than otherwise could be secured. It hasbeen found also that the delay time is less influenced by the amplitude of the input pulses and also less influenced by the repetition rate of the pulses when the rectifying element is employed.

What is claimed is:

1. A multivibrator comprising two spaced discharge devices each having an anode, a cathode and a grid, a first coupling means coupling the anode of the first space discharge device to the grid of the second, a second coupling means coupling the anode of the second space discharge device to the grid of the first,,a circuit decoupled with respect to said second coupling means for impressing a unidirectional control impulse upon the grid of the first space discharge device, a direct-current path including a transformer 3. A multivibrator comprising two space discharge devices each having an anode, a cathode and a grid, said cathodes being connected to a common cathode terminal, a source of current supply for said space discharge devices, a feedback resistor connected between said common cathode terminal and the negative side of said source of current supply, a capacitor connected between the anode of the first said space discharge device and the grid of the second said space discharge device, a fixed resistor connected between the grid of the second space discharge device and the positive side of said source of current supply, a primary winding of a load transformer connected between the positive side of the source of current supply and the anode of the second space discharge device, and an adjustable timing resistor connected between the positive side of the source of current supply and the anode of the first space discharge device.

4. vAmultivibrator comprising two space discharge devices each having an anode, a cathode and a grid, a first coupling means coupling the anode of the first space discharge device to the grid of the second, a second coupling means coupling the anode of the second space discharge device to the grid of the first, a grid leak resistor in circuit between the grid and cathode of the first space discharge device and having substantially no coupling with said second coupling means, a control impulse supply path of relatively low impedance compared to said grid leak resistor, said control impulse supply path being in parallel connection with said grid leak resistor, and with the grid cathode path of said first space discharge device and including in series connection a transformer winding of relatively low direct-current resistance, and'a substantially unidirectional conductor serially connected with said transformer winding in said control impulse supply path and having its direction of conductivity in the direction of flow of the impressed trans- ALFRED S. GANO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Stratton Aug. 1, 1944 Number 8 Name Date Schrader et a1 Nov. 28, 1944 Miller et a1 Dec. 11, 1945 Koenig July 16, 1946 Ruhlig Aug. 6, 1946 Goldkey Aug. 13, 1946 Moe Jan. 14, 1947 Yetter Apr. 8, 1947 Kahn Aug. 5, 1947

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