US2797317A

US2797317A - Wave generation circuits

Info

Publication number: US2797317A
Application number: US279975A
Authority: US
Inventors: Laurance M Leeds
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1952-04-02
Filing date: 1952-04-02
Publication date: 1957-06-25
Anticipated expiration: 1974-06-25

Description

June 25, 1957 A M. LEEDS 2,797,317

WAVE GENERATION CIRCUITS Filed April 2, 1952 Inventor- Laurence M. Leeds,

b m M His Attorney.

United States Patent WAVE GENERATION CIRCUITS Laurance M. Leeds, Syracuse, N. Y., assignor to General Electric Company, a corporation of New York Application April 2, 1952, Serial No. 279,975

1 Claim. (Cl. 250=-27) The present invention relates generally to electrical wave generation circuits and particularly to such circuits in which pulses are generated in response to initiating impulses.

An object of the present invention is to provide improved means for varying the duration of said pulses.

Wave generation circuits of the above-described kind commonly used for the generation of pulses include a pair of electron discharge devices which are interconnected in a manner so as to be alternately conductive and so that when an initiating pulse is applied to said devices, one of said devices becomes conductive and the other hecomes nonconductive, and said one device becomes nonconductive again after a predetermined interval of time determined by the constants of the circuit, thereby developing a pulse of current in said one device. The initiating impulses are usually applied to the grid of one of said devices to initiate pulses of current in said one device and a unidirectional potential variable in magnitude is applied to the grid of the other of said devices to vary the duration of said pulses in accordance with the magnitude of said potential.

The latter arrangement for controlling the duration of pulses is particularly suitable where the wave generation circuit must be capable of being controlled from a remote location. When the duration of the pulses are controlled in this way, the range over which the duration of pulses may be varied is limited.

Accordingly, another object of my present invention is to provide improved means for varying the duration of pulses over a greater range.

In carrying my invention into effect, circuit means are provided in association. with said electron discharge devices to decrease the duration of the short pulses and increase the duration of the long pulses which would be obtainable-without said circuit means.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claim. 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 drawing which shows an embodiment of my invention.

In this embodiment are shown electron discharge devices 1 and 2 having respective cathodes 3 and 4,

respective grids

5 and 6, and respective anodes 7 and 8. The anodes 7 and 8 are connected through respective resistances 9 and 16 to the positive terminal 11 of a source 12 of unidirectional operating voltage.

The cathodes 3 and 4 are connected together and are also connected through cathode resistance 13, and through capacitance 14 and resistance 15 in series, to the negative terminal 16 of the source 12 to which is also connected input terminal 16' and output terminal 16".

Grid 5 is connected to the junction of

resistances

17 and 18, which are arranged in series across the source 12, and is also connected to input terminal 19. Grid 6 7 2,797,317 Patented June 25, 1957 ice is connected through resistance 20 and conductor 24 to variable tap 21 of voltage divider 22 which is connected across the source 12. The conductor 24 between resistance 20 and variable tap 21 is shown broken to indicate that the voltage divider 22 may be situated at a remote location from the remainder of the circuit. The end of resistance 20 remote from the grid 6 is bypassed to ground by bypass capacitor 23.

Anode 7 is connected to grid 6 through coupling capacitor 25. Anode 8 is connected through output coupling capacitor 26 to output terminal 27.

In operation, the device 2 is normally conducting since grid 6 is connected to a positive potential on voltage divider 22, and a potential is developed across cathode resistance 13 sufficient to maintain the device 1 nonconducting. The capacitance 25 is charged to a voltage which is the difference in potential of anode 7 and grid 6. When a triggering impulse 28 is applied to the input terminals 16', 19 to render grid 5 sufficiently less negative than cathode 3 for a short interval of time, device 1 becomes conducting. The drop in potential at anode 7 produced by conduction in device 1 is applied throughcapacitor 25, which has been charged to a certain voltage as pointed out above, to grid 6 of device 2 to reduce conduction in the latter device. The decrease in potential across resistance 13 produced by a decrease in conduction of device 2 causes a decrease in potential atcathode 3 of device 1 and thus causes an increase in conduction of device 1. Accordingly, after a very short interval of time the device 1 becomes completely conductive and the device 2 becomes completely nonconductive.

The devices 1 and 2 remain in this state until the charge on the capacitance 25 decays sufiiciently primarily through resistances 9 and 20 so that the potential at the grid 6 rises sufliciently to render the device 2 again conductive. When device 2 becomes conductive a bias is developed across resistance 13 which renders device 1 nonconductive. Thus, in response to a triggering pulse 28 of short duration, a pulse of voltage represented by graph 29 is produced at anode 8. a

The interval in which device 2 is nonconductive, and hence the duration of the pulse 29, is determined by the positive potential applied to the grid 6. The greater in magnitude this positive potential is, the shorter is the duration of the pulse 29. The reason for this can be readily appreciated from the fact that capacitance 25 is charged to substantially the same voltage whether the pulse is short or long and that the higher the potential to which the grid end of capacitance 25 must charge after this end has been lowered in potential by a drop in'the potential at anode 7, the greater will be the rate of change of potential at this end, and thus, the potential at grid 6 to cause conduction in device 2 is reached sooner, thereby resulting in a pulse of voltage at anode 8 shorter in duration.

The short pulses may be further shortened and the long pulses may be further lengthened by means of the circuit comprising capacitance 14 and resistance 15. During the time device 2 is conducting, the capacitance 14 becomes charged to the potential of cathode 4 and after the triggering impulse is applied to device 1, capacitance 14- tends to maintain the cathode 3 at the potential existing before the application of pulse 28. Thus the drop in the potential of the anode 7 does not reach its ultimate value until the charge on capacitance 14 can decay. The decay in charge on the capacitance 14 is delayed sufiiciently by

resistances

13 and 15 in the discharge circuit of the capacitance so that the drop in potential at the anode 7 to its ultimate value is delayed longer than the duration of a short pulse and shorter than the duration of a long pulse. The short pulse is shortened by this delay because the grid 6 is not lowered to as low a potential when device 1 becomes conducting as it would were capacitance 14 and resistance 15 out of circuit. The long pulse is lengthened by this delay because the grid is progressively dropped in potential in a manner such that it takes a longer time for the capacitance to be discharged to a potential to render device 2 conductive after it has been rendered nonconductive. The capacitance 14, resistance 15, and resistance 13 are proportioned to produce the desired delay. It should be noted that other circuit elements function ing to produce the desired delay characteristic may be used in place of the capacitance 14 and resistance 15 combination.

Circuit elements having the following values have proved very satisfactory:

Device 1 tube type 5,963 Device 2 do 5,963 Resistance 13 ohms 2,400 Capacitance 14 micro microfarads 3,300 Resistance 15 ohms 3,000 Resistance 9 do 47,000 Resistance do 10,000 Capacitance 25 micro microfarads 47 Resistance 17 ohms 470,000 Resistance 18 do 33,000 Resistance 20 do 160,000 Capacitance 23 microfarad 0.1

These values are given as examples and are not to be construed as limitations since other values will work equally as well. 7

When capacitance 14 and resistance are disconnected from the circuit and the voltage point to which grid 6 is connected is adjusted from 275 volts to 55 volts the output pulse changes in time length from 3.5 microseconds to 11 microseconds, respectively. When capacitance 14 and resistance 15 are connected in circuit as shown and the voltage point to which grid 6 is connected is adjusted from 275 volts to 55 volts the output pulse changes from 1.5 microseconds to 14 microseconds. Thus with the addition of capacitance 14 and resistance 15 the ratio of maximum to minimum pulse length was substantially increased from 3.14 to 9.3.

Thus applicant has provided simple yet highly effective means for extending the range over which the duration of pulses may be varied, particularly when his desired to control the duration of the pulses from a location remote from circuit such as in television systems, for example.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since many modifications, both in the circuit arrangement and in the instrumentali- 4 ties employed, may be made, and I, therefore, contemplate by the appended claim 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 by Letters Patent of the United States is:

The combination, in a system for generating a pulse of an adjustable interval in response to an impulse applied thereto, of a pair of electron discharge devices each having an anode, a cathode, and a control grid, 4

a source of operating potential connected between the anode of each of said devices and the cathode thereof, circuit means for rendering either of said devices conductive when the other is non-conductive, means to apply said impulse to one of said devices to render conductive that one device which is nonconductive whereby the other device becomes nonconductive, a first resistance between said source and the anode of said one device, a first capacitance between the anode of said one device and the grid of said other device, and a second resistance between the cathodes of said devices and said source, whereby upon termination of said impulse said other device is maintained nonconductive and said one device is maintained conductive for a predetermined interval by the charge on said first capacitance, adjustable means for applying a potential to the grid of one of said devices for altering the rate of discharge of said first capacitance, thereby altering the duration of said interval, a third resistance and a second capacitance connected in series across said second resistance, said second resistance having a magnitude substantially equal to that of said third resistance, and the discharge circuit of said second capacitance having an effective time constant of the order of magnitude of that of the discharge circuit of said first capacitance, whereby the minimum adjustable interval of said pulse may be decreased and the maximum adjustable interval of said pulse may be increased beyond that obtainable without said third resistance and said second capacitance.

References Cited in the file of this patent UNITED STATES PATENTS 2,405,237 Ruhlig Aug. 6, 1946 2,492,736 Custin Dec. 27, 1949 2,494,353 Newman Jan. 10, 1950 2,500,788 Bass Mar. 14, 1950 2,562,171 Butman July 31, 1951 2,602,890 Gains July 8, 1952 2,648,004 Wheeler Aug. 4, 1953 FOREIGN PATENTS 617,788 Great Britain Feb. 11, 1947