US2979660A - Provision of a predetermined pulse responsive to a trigger pulse with provision for adjustable delay - Google Patents

Description

April 11, 1961 R. D. WlLLlAMS 2,979,660

PROVISION OF A PREDETERMINED PULSE RESPONSIVE TO A TRIGGER PULSE WITH PROVISION FOR ADJUSTABLE DELAY Filed NOV. 30. 1955 INVENTOR R065 0 W/LL IAMS 7 villi;

PROVISION OF A PREDETERMINED PULSE RE- SPONSIVE TO A TRIGGER PULSE WITH PRO- .VISION FOR ADJUSTABLE DELAY Roger D. Williams, Northport, N.Y., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Nov. 30,1955, Ser. No. 550,231

3 Claims. Cl. 328-67) This invention relates to pulse delay circuits and more particularly to a circuit capable of providing a pulse output at a controlled delay with respect to a trigger pulse applied thereto.

It is the primary object of the present invention to provide. a pulse generating circuit which is capable of producing pulses at a continuously adjustable delay in response to respective trigger pulses.

It is a further object to provide a time modulator circuit wherein modulation can be performed at high levels with low driving power.

Other objects and many of the attendant advantages of this'invention will be readily appreciated as the same becomes better understood by reference to the following detaileddescription when considered in connection with the accompanying drawing wherein:

The single figure is a schematic circuit diagram, partially in block form, of an embodiment of this invention.

Briefly, the circuit of the present invention provides a pulse from a circuit including a gaseous electrical discharge tube having a cathode, plate and control electrode ata controlled delay'with'respect to a trigger pulse, the controlled delay being adjustable over a wide range. 'Control'of delay is obtained, within the duration time of the trigger pulse at the control electrode of the gaseous discharge tube, by adjusting the amplitude of the trigger pulse at the control electrode of the gaseous discharge tube to thereby adjust the plate to cathode breakdown time of the gaseous discharge tube.

One of the inherent characteristics of a gaseous electrical discharge tube such as a thyratron is the mechanism of its breakdown. Thyratron breakdown is apparently divided into two partsbetween grid and cathode first followed by plate cathode-breakdown. This invention is concerned with the time of occurrence of the plate cathode breakdown. Where a positive-going pulse is applied to the thyratron grid to cause grid cathode breakdown and then plate cathode breakdown, the shape of the pulse is apparently inconsequential so long as it is maintained until breakdown can occur. This factor enables the use of a stretched pulse as a trigger in the circuit and the ignoring of shaping except to the extent that there is concern with minimum available delays achievable from supply voltages and maximum delays achievable with the amplitude regulation of a trigger pulse applied to the thyratron grid.

Referring now to the drawing, a negative going trigger pulse is applied from trigger pulse source to the cathode 11 of a diode 12. The plate 13 of diode 12 is connected through a resistor 14 to variable voltage source 16 legended as a delay control voltage source, such as a source of modulating voltage. Cathode 11 is connected to voltage source 16 through a resistor 15, whereby cathode 11 and plate 13 are maintained at the same potential when tube 12 is in the quiescent state. Plate 13 i connected to the control grid 20 of a remote cutoff video amplifier comprising a tetrode 18 having a grounded cathode 22, control grid 20, a screen grid 24 and a plate 26, plate 26 being connected to a suitable source of B+ potential 28 through a series arrangement of an inductance 30 and a resistance 32. Screen grid 24 is connected to a source of B-lpotential 34 through a resistance 36. Inductance 30 is included in the plate circuit of tetrode 18 to compensate for output capacitance at higher frequencies.

'It is to be seen that resistor 14 and the input capacity 38 of tetrode 18 form a time constantcircuit. Such circuit has the eflect of providing a stretched 'trigger pulse at the control grid of tetrode 18 in response to each trigger pulse applied to cathode 11 of diode12.

Considering the effect of the delay control voltage it is to be noted that when the voltage applied from delay con- Plate 26 of tetrode 18 is coupled tothe input of a cathode follower through a capacitance 40. The cathode follower comprises a tetrode 42 having a plate 44 and a screen grid 46 connected to suitable sources of B+ potential 48 and 50 respectively and a cathode 52 connected to groundthrough a resistance 54. I The control grid 56 of tetrode 42 is connected through a resistance 58 to an adjustable direct current voltage source 60 which may. .be varied from ground to a desired positive potential.

The output at cathode 52 is applied to the control grid 63 of a thyratron 62 having a grounded cathode 64 and a plate 66 connected to a source of B+ potential 68 through a suitable pulse forming network such as arti ficial transmission line 70. The output of thyratron 62 may be taken from transformer 72. e

the bias voltage applied to grid 63. If the bias potential on grid 63 is optimized in the positive direction, the range of delay obtainable by variation of voltage source 16 is a minimum. Conversely, if the bias potential on grid 63 is optimized in the negative direction, the range of delay obtainable by variation of voltage source 16 is a maximum. To illustrate by the use of numbers, the range of delaymay be from 0.1 microsecond to 3 microseconds when the bias potential is optimized in the positive direction on grid 63 and from 0.1 microsecond to 40 microseconds when the bias potential is optimized in the negative direction.

Thus, with the present circuit, the inherent characteristics of a thyratron are utilized to achieve deliberately controllable variable delays from the input trigger by means of precise control of the input trigger pulse amplitude and duration and without variation of thyratron circuit parameters.

In a typical circuit, diode 12 may be a 12AT7 tube, resistance 14 is a 1 megohm resistor, tetrodes 18 and 42 are 807W tubes, thyratron 62 is a 4C35 tube, B+ source 34, 28, 50, and 48 are at 300, 600, 300 and 600 volts respectively, B+ source 68 is at 4000 volts, and delay control source 16 is variable between ground and volts. With the typical circuit outlined, a minimum available delay as low as 0.1 microsecond and delay variations to 10 microseconds can be achieved. A low level thyratron such as a 2D2l or 2050 may be used in this type of circuit in place of the 4C35 but not with positive control grid bias voltage. In such a case, cathode 52 of tube 42 in the cathode follower stage would have to be connected through resistor 54 to a suitable source of negative potential.

The present circuit can be used as a time modulator.

Patented Apr. 11, 1961" which the secondthyratron fires can be controlled by taking the output voltage of the first thyratron, controlling its amplitude and applying it as a trigger to the secnd thyratron. 7

Obviously many'modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

I claim:

1. A circuit comprising a diode having a cathode and anode; a variable voltage source, said diode cathode and anode being connected to said voltage; source through first and second resistors respectively; a video, amplifier including a vacuum tube having at least acathode, control grid, and plate, said tube having its control grid coupled to said diode anode whereby the input capacity of said vacuum tube and said second resistor form a time constant circuit that increases the duration of an output negative going trigger pulse above that of the input negative going trigger pulse applied to said diode; a thyratron having a cathode, plate and control electrode and having a pulse forming network in its plate circuit; and adjustable thyratron bias voltage control means having its input coupled to the output of said video amplifier and its output'coupled'to the input of said thyratron for biasing,

In the latter, two thyratrons are often used 2,979,660 v H 7 r follower including a vacuum tube having at least a cathode, plate and control electrode, said last-mentioned convariable voltagemeans coupled to said pulse stretching means for selectively controlling the amplitude of stretched pulses from said pulse stretching ,means; a gaseous'electrical discharge tube having acathode, plate and control electrode; a voltage source for feeding current from plate to cathode of said tube; a pulse forming network connected to said voltage source and said plate; said tube permitting current to. flow from. P131610 cathode when the voltage between said control electrode, and said cathodeis raised above a predeterminedlevelim the positive direction and for a continuous interval sufli cient for plate to cathode breakdown; adjustable bias means coupling said pulse stretching means andsaid con trol electrodefor normally biasing said control electrode so that said gaseous tube is nonconductingand' for delivering stretched trigger pulses from saidpulsestretching meansto said control electrodef whereby said pulse forming network provides a delayed output pulsc follow-'- ing each trigger pulse; and whereby therangeof delay in plate to cathode breakdown in said gaseoustube is de-' termined by the selected adjustment of said bias means" and the particular delay within the adjusted range is -determined by the voltage output of said variable voltage means.

References Cited in theme of this patent UNITED STATES PATENTS 2,411,130 Evans Nov. 12, 1946' 2,467,793 Wheeler Apr. 19, 1949' 2,579,473 Chatterjea Dec. 25, 1951.

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