US2745959A - Trigger circuits - Google Patents

Description

y 5, 1956 A. R. KlLBEY ET AL 2,745,959

TRIGGER CIRCUITS Filed 001;. 24, 1952 {20 I M II /4 SIGNAL 25 SOURCE l BIASED CLIPPER GRID PLATE SCREEN 28 F76. 2

I 29 I sum/2155012 I II OUTPUT I 35 K 36 f. I 1 INVENTOPS is 4 I ALFRED l2 K/LBEY ,3, 650/265 5 Tue/ 19? ATTORNEY United States Patent TRIGGER CIRCUITS Alfred R. Kilbey, Albuquerque, N. Mex., and George E.

Tucker, Waltharn, Mass., assignors to Raytheon Manufacturing Company, Newton, Mass., a corporation of Delaware Application October 24, 1952, Serial No. 316,622

Claims. (Cl. 25027) This invention relates to electron discharge systems and more particularly to devices used for generating trigger impulses.

Many devices for generating trigger impulses in response. to control signals are known in the art. For example, multivibrators or over-driven amplifiers, with differentiating circuits have been often used to produce steep wave front output signals for triggering purposes with the time position of the wave front governed by input control signal which may vary in frequency amplitude phase, or any other desired characteristic. Such devices, in general, have several disadvantages. For example, in the case of controlled multivibrators, the time position of the output Wave front has a tendency to jitter about an average position, which is a function of the control signal, particularly if the control signal in itself does not have steep wave front characteristics. in addition, the power requirements of such devices are usually relatively high, since the major conduction paths on the circuits pass current for a relatively large percentage of the cycle.

This invention discloses a device whereby a steep wave front output may be produced in response to a control wave, which does not possess a steep wave front, with substantially no jitter of the output wave about a mean time position. Briefly, this is accomplished by the use of an electron discharge device whose cathode has a reactive impedance in circuit therewith and whose anode has a reactive impedance circuit therewith which will resonate with the reactive impedance in circuit with the cathode when the discharge device is conducting. The control wave form is applied to a control grid of the discharge device through a current-limiting resistor, and is of sufficient amplitude that the control grid is periodically driven positive into saturation of the control characteristic of the device and then back negative to a point beyond the cut-01f voltage of the control grid. During conduction between the anode and cathode, the reactive impedance in the anode circuit of the device, which may be, for example, a condenser, discharges through the reactance impedance of the cathode circuit of the device, which may be, for example, an inductance, creating a pip, the steepness of which is a function of the resonant frequency of the condenser in the anode circuit and the inductor in the cathode circuit. In order to achieve a steep wave front, the resonant frequency of the condenser and inductance should be much higher than the repetition rate of the control wave. The number of cycles through which the resonance condition of the condenser and inductance exist may be determined by the period of conduction of the device.

This invention also discloses that the anode-cathode conductive path of the electron discharge device may be cut off even though the grid remains driven positive for a substantial portion of a cycle of the control wave form. Briefly, this is accomplished by the use of a screen grid and a suppressor grid in conjunction with a control grid in the electron discharge device. The screen grid is connected in circuit. with a load such that an excursion of the grid wave form positive drives the screen grid in a negative direction. The voltage wave form on the screen grid is then coupled to the suppressor grid, for example, through a condenser such that the suppressor grid. is driven negative as the control grid is driven positive, thereby cutting off anode-cathode conduction of the device after the control grid. has been driven in a positive direction by a relatively small amount. The result is that the device conducts from the cathode to the anode once when the grid. is driven. positive and once when the grid is driven negative. Thus the device may also be used as a frequency doubler, since the plate wave form has a frequency. twice. that of the control wave form applied to the grid.

Other and further objects and advantage-sf of this invention will be apparent as the description thereof progresses, reference being had to the accompanying drawings, wherein:

Fig. 1 illustrates a circuit diagram of an electron discharge system embodying this invention; and

Fig. 2 represents aseries of wave forms obtained at various points in the circuit of the system shown.

Referring now to Fig. 1, there is shown a pentode 10 having a cathode 11 connected to ground through an inductance 12. The control grid 13 of pentode 10' is connected to a signal source 14 through a grid-limiting resistor 15. Signal source 14 is also connected to ground, such that the grid 13 has a zero bias potential.

The screen grid 16 of pentode 10v is connected to B+ through a load resistor 17 and to the suppressor grid 18 of pentode 10 through a resistor 19 and condenser 29 in parallel. Suppressor grid 18 is also connected to ground through a resistor 21. The anode 22 of pentode 10 is connected through 13+ to a resistor 23 and condenser 24 in parallel.

The output of the device is developed across. inductor 12 and is fed through a clipper 25 to any desired utilization device. Clipper 25 is shown by way of example, only, and may be, for example, a diode having a polarity such that it clips off either the negative or positive half of the output signal, depending upon which polarity of output pslse is desired.

Referring now to Fig. 2, the operation of the device will be described. The signal source 14 is indicated as producing a sine wave 26, which may vary in phase, amplitude, frequency, or D. C. reference levels, and as shown here may have an amplitude of from ten to fifty volts R. M. S., the chief criterion being that the amplitude of the wave be sufficient to drive the pentode 10, for example, a type 6AS6-or type 5784, into saturation on the positive excursion of the Wave form and into cut-0E on the negative excursion thereof.

After passing through the grid current-limiting resistor 15, the wave form 26 is applied to the grid as modified wave form 27, which has the positive portion thereof substantially entirely clipped off due to the drawing of grid current from the cathode 11 to the grid 13, thereby creating a drop across resistor 15. Good clipping action may be achieved with the limiting resistor 15 having a value on the order of a megohm or more.

The wave form produced at the screen 16 across the load resistor 17 is substantially a square wave, as shown at 28, with the negative excursion of the square wave being merely an amplification of the clip positive portion of the wave applied to the grid 13 and the positive of the excursion appearing on the screen being produced by driving the grid 13 below the cut-off by the negative excursion of the wave form applied to the grid. This wave form is coupled through the condenser 20, which is sufliciently large to prevent any substantial difierentiation of the wave form on the screen and appears substantially as a square wave 29 applied to the suppressor grid.

.The suppressor grid 18 has a bias maintained thereon, which is produced by the resistance of the resistor 21 and the bleeder resistor 19. Good operation may be achieved with an average suppressor grid bias on the order of plus five to ten volts with a 13-}- potential on the order of 150 volts. Thus it may be seen that, as the grid 13 is first driven positive, the screen grid is driven negative, thereby driving the suppressor grid negative. As a result the anode 22 receives electrons for a short period of time after the grid has gone positive and before the suppressor grid has gone sufficiently negative to cut off the anode-cathode conductive path, thereby producing a negative excursion of the plate, as at 30, charging the condenser 24, such that the side thereof connected to the anode 22 is negative with respect to B-]-. Condenser 24 then discharges gradually through the resistor 23, producing the exponential wave form shown at 31.

When the grid is driven negative out of saturation, it drives the screen grid 16 in a positive direction, thereby driving the suppressor grid 18, which is coupled to the screen grid 16, positive and rendering the path between the anode 22 and the cathode 11 conductive for a somewhat longer period of time than when the grid was driven positive. The time duration or" the conductive period of the anode depends upon the time required for the grid 13 to pass from saturation, as indicated by point 32 on curve 27, to cut-oft, as indicated by point 33 on curve 27. During this period the conduction from the cathode 11 to the anode 22 causes a voltage rise to develop across the inductor 12 in the cathode circuit, producing a positive excursion of an output wave form as at 34. The inductor 12 resonates with the condenser 24 to produce a full cycle of oscillation having a negative excursion 35, as well as a positive excursion 34, before the grid 13 is driven into the cut-oif,

disrupting the conductive path between the cathode 11 and the anode 22 and thereby interrupting the resonance action of the condenser 24 and the inductor 12. The output wave form 35 has been shown expanded in time as at 36 to indicate that the output wave form is substantially sinusoidal. It is to be clearly understood that more than one cycle of the wave output form could be achieved, if desired, by allowing a longer period of time to elapse during which the grid 13 passes from its saturated condition to its cut-off condition.

Thus it may be seen that a sharp, positive pip may be generated at the cathode when the grid is driven from saturation to cut-01f. It has been found that no such sharp positive pip occurs when the grid is driven from cut-off to saturation; rather a small positive excursion 37 is observed as the grid is driven positive. This small excursion may be clipped off by suitably biasing the clipper 25 according to well-known practice.

It may be clearly seen that the plate wave form has a positive and negative excursion for every positive and negative excursion of the input wave form. Therefore, the plate wave form has a large component of the sec ond harmonic of the input wave form. Consequently, the wave form on the plate may be used as the output wave form in applications where it is desired that the device could be used as a frequency doubler. A substantially rectangular-shaped wave form is available at the screenv grid, if desired.

This completes the description of the specific embodiment of the invention described herein. modifications thereof will be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For example, the condenser 24 could However, many be returned to ground rather than to B+ and other multiple element electron discharge devices could be used in place of the pentode 10. In addition, signal source 14 need not necessarily be a sinusoidal source, but could be a source of triangular waves or waves of any other desired shape. Accordingly, it is desired that this invention be not limited by the particular details of the embodiment described herein, except as defined by the appended claims.

What is claimed is:

1. An electron discharge system comprising a cathode, a reactive impedance in circuit with said cathode, an anode spaced from said cathode, a reactive impedance in circuit with said anode which will resonate with the reactive impedance in circuit with said cathode during conduction between said anode and said cathode, and means for controlling the conduction between said anode and said cathode.

2. An electron discharge system comprising a cathode, a reactive impedance in circuit with said cathode, an anode spaced from said cathode, a reactive impedance in circuit with said anode which will resonate with the reactive impedance in circuit with said cathode during conduction between said anode and said cathode, a control grid, a screen grid, and a suppressor grid all positioned between said source and said anode, means for coupling a signal source to said control grid, an impedance load coupled to said screen grid, and means for coupling said screen grid to said suppressor grid.

3. An electron discharge system comprising a cathode, a reactive impedance in circuit with said cathode, an anode spaced from said cathode, a reactive impedance in circuit with said anode which will resonate with the reactive impedance in circuit with said cathode during conduction between said anode and said cathode, a plurality of grids positioned between said source and said anode, means for coupling a signal source to a first of said grids, an impedance load coupled toa second of said grids, and means for coupling said second grid to a third of said grids.

4. An electron discharge system comprising a cathode, a reactive impedance in circuit with said cathode, an anode spaced from said cathode, a reactive impedance in circuit with said anode which will resonate with the reactive impedance in circuit with said cathode during conduction between said anode and said cathode, a control grid, a screen grid, and a suppressor grid all positioned between said source and said anode, means for coupling a signal source to said control grid, the amplitude of signals from said signal source being greater than the control range of said control grid, an impedance load coupled to said screen grids, and means for coupling said screen grid to said suppressor grid.

5. An electron discharge system comprising a cathode, a reactive impedance in circuit with said cathode, an anode spaced from said cathode, a reactive impedance in circuit with said anode which will resonate with the reactive impedance in circuit with said cathode during conduction between said anode and said cathode, a plurality of grids positioned between said source and said anode, means for coupling a signal source to a first of said grids, the amplitude of signals from said signal source being greater than the control range of said first grid, an impedance load coupled to a second of said grids, and means for coupling said second grid to a third of said grids.

References Cited in the file of this patent UNITED STATES PATENTS 2,172,746 Young Sept. 12, 1939 2,456,029 Snyder Dec. 14, 1948 2,695,962 Nibbe Nov. 30, 1954

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