US2700732A

US2700732A - Pulse stretcher

Info

Publication number: US2700732A
Application number: US635784A
Authority: US
Inventors: Jr James V Holdam; Lloyd M Jones
Original assignee: Individual
Current assignee: Individual
Priority date: 1945-12-18
Filing date: 1945-12-18
Publication date: 1955-01-25
Anticipated expiration: 1972-01-25

Description

Jan. 25, 1955 J. v. HOLDAM, JR,, ETAL 2,700,732

PULSE S'I RETCHER Filed Dec. 18, 1945 INVENTORS JAMES VANCE HOLDAM JR.

LLOYD M JONES ATTORNEY United States Patent PULSE STRETCHER Jam s V. Holdam, In. Camb idge, Mas and Lloyd Jones, Los Angeles, Calif assianor by mesne m n s, to the United S ates of Ameri as rep esen by the Secretary of the Navy Application December .18, 194 S ria No- 8 3 C a ms- (c1; 250-21) This invention relat s o Pulse stretches, par i ularly hose which respond in tantaneou ly to bo h ncreases or decreases in th magnitude of he pulses impre sed thereon.

In gun lay ng ad r quipm nt, it is necessa y to stretch each video pulse of a series until the ccurren of the succeeding video pulse in order to keep up a reference frame corresponding to the envelope of the series of vido pulses and thus maintain the voltage necessary to train the guns. This Pulse stretching has been accomplished by using a long time constant circuit in the output of a cathode follower or rectifier and utilizing the voltage existing across the time constant circuit to control the grid of the electron tube of the succeeding amplifier stage. This met od has the disa van age f not being able instantanenously to respond to both increases and decreases in magnitude of the series of pulses to be stretched. Due to the rectifying act on of the rectifier or cathode follower an increase in magnitude would instantaneously be indicated as a voltage increase across the time constant circuit, but a decrease in magnitude would not be registered until .the time constant circuit had discharged :1 corresponding amount. To shorten the time constant of the circuit would render the pulse stretcher less effective as such, due to the voltage decrease in magnitude of the stretched pulse with time. To overcome this, schemes were proposed to short the time constant circuit by a delayed trigger shortly before the occurrence .of each pulse of the series to be stretched and thus prepare the time constant circuit for the pulse. This had the disadvantago that the pulses were not stretched over the entire priod between pulses, and that a trigger circuit was required with the accompanying complexity.

It is accordingly an object of this invention to provide a pulse stretcher that responds instantaneously to both increases and decrea es the magnitude of the pulses impressed thereon.

'It is a further object .of this invention to provide a pulse stretcher that does not require a trigger circuit to respond instantaneously to both increases and decreases in the magnitude of the pulses impressed thereon.

These and other objects will be more apparent upon consideration of the following specification together with the accompanying drawing, which discloses a circuit diagram of an embodiment of the invention.

In the drawing the series of pulses to be stretched is applied to terminal 10 to be impressed on the grid of electron tube 11 and provide suitable bias for this grid by means of the conventional grid biasing circuit 12 associated therewith. Tube 11 has its anode and cathode joined with a source of plate potential and ground by resistors 13 and 14, respectively. Anode resistor 13 has a larger resistance than cathode resistor 14. Thus the pulses produced at the cathode and plate simultaneously with each pulse impressed on the grid will have different magnitudes and opposite polarities. It is thus seen that tube 11 functions as a phase splitter. The negative anode pulses will be greater than the positive cathode pulses, assuming that the pulses impressed on the grid are positive.

A pair of rectifiers, in the

instant embodiment diodes

15 and 16, have one of their anodes and cathodes joined together, while the free cathode of diode 15 is connected with the plate of electron tube 11 through blocking condenser 17 and the free anode of diode 16 is con- 2,700,732 Patented Jan. 25, 1955 t d di c ly to t e a od o el c on t 11- The joine anode nd ca h o d od s d 6 r connec d to r nd h ugh apa or 18 s d r n now t e ct n o t e c u t al y d bed apac t r 1 l ha e ss m d a c a qu t e rence in potential between the anode of tube 11 and the oathode o t b 1. There l be no p te ti l d p oss resistor 25 since capacitor 17 will reach a fully charged c nd ion i the n er al b t n c e ve Pu s sri r t h applic n of a pu e a ter na 1 the auode of diode 16 will be at some low potential, for example, ground potential if tube 11 is completely out oif, while the cathode of diode 16 will be at the potent al o h ch pa t r 18 s ha e Sin he de of diode 16 is negative with respect to the cathode, diode 18 will be nonconducting. Diode 15 will also be nonnd c g tor e reas n that th a de of d d is at the potential of the grid of tube 19, while the cathode of diode 15 is at the potential of the cathode of tube 19 which i ssu e a P t nt al g y P s t e wi h espe t to he idhu e c t d of tub 5 s p sitive with respect to the anode, Assume for the moment th a p s i e pu se i appl ed to e in re l in a positive and a negative pulse appearing at the cathode and anode respectively of tube 11. Assume further ha t e pul e pp ar n a t e a od of be 1 s an amplitude greater than the potential to which capacitor 18 is charged. The anode of diode 16 will then become positive with respect to the cathode and the resulting current flow through diode 16 will tend to charge capacitor 18 to the potential of the cathode of tube 11. The negative pulse at the anode of tube 11 will be coupled through capacitor 17 to the cathode of diode 15, making the cathode of diode 15 negative with respect to the anode of this tube. Current flow through diode 15 is in a direction tending to reduce the potential on capacitor 18 and also to reduce the potential on the capacitor 17. However, the potential on capacitor 18 cannot be lowered below the potential of the cathode of tube 11 since the current flow through diode 16 will restore charge on capacitor 18 removed by the current flow through diode 1 5. The net result is that capacitor 18 assumes a potential equal to the amplitude of the pulse at the cathode of tube 11, and the capacitor 17 assumes a potential equal to the difference between the potential .on capacitor 18 and the potential at the anode of tube 11 during the negative pulse ,at this anode. Un der this condition, the difference in potential between the cathode of diode 15 and the cathode of tube 19 will appear across resistor 25.

Following the termination of the pulse at terminal 19, the anode of diode '16 becomes negative with respect to the cathode of this tube and the cathode of diode 15 becomes positive with respect to the anode of this tube, thus blocking in the discharge path from capacitor 18. In the interval before the next pulse is applied to terminal 10, capacitor 17 will again be charged to the difference between the potential at the anode of tube 11 and the new potential at the cathode of tube 19. The charging of capacitor 17 takes place through

resistors

13, 25 and 20.

Assume now that a second pulse is applied to terminal 10 and that this pulse has an amplitude such that the pulse at the cathode of tube 11 has an amplitude less than the potential on capacitor 18. Under these circumstances, initially, the anode of diode 16 will still be negative with respect to the cathode of this tube and no conduction will take place through diode 16. However, the cathode of diode 15 will become negative with respect to the anode of this tube since diode 15 is held nonconducting only by the amount of the grid to cathode bias on tube 19. Diode 15 will then conduct causing capacitor 18 to discharge through diode 15. When the potential on capacitor 18 has dropped to the potential at the cathode of tube 11, diode 16 will begin to conduct preventing any further drop in the potential to which capacitor 18 is charged. The operation of the circuit from this time on will be identical to the operation as described in connection with the application of the first pulse to terminal 10. Since the diodes have a low resistance during conduction, the charging and discharging paths including capacitor 18 will have an extremely short time constant during occurrence of the pulse to be stretched. This permits an extremely rapid response of the capacitor voltage to any change in the magnitude of the pulses applied at terminal 10.

An amplifier circuit including electron tube 19, cathode resistor 20 and anode resistor 21 is provided. The grid of tube 19 is connected directly with the charged terminal of capacitor 13. Thus the voltage changes across capacitor 18 appear amplified across resistor 21. A variable tap is provided on resistor 21 to permit abstraction therefrom of the desired degree of voltage change to be impressed on the electron tube 22 of the subsequent circuit, in the instant embodiment a phase splitter, Whose outputs are abstracted at terminals 23 and 24 for any desired purpose-here to control an indicator. Adjustment of the variable tap permits voltage changes to be secured thereat proportional to changes in the magnitudes of the pulses of the series impressed terminal 10.

A leakage resistor 25 connects the cathode of diode 15 with the cathode of tube 20. This resistor prevents the negative pulse from resistor 13 from being shorted across resistor 20. The cathode of diode id is connected thus to the cathode of tube 19 so that the cathode-anode bias of diode 15, necessary to prevent a leakage path for capacitor 18, remains essentially independent of the existing charge on capacitor 18.

Suitable values of certain of the circuit constants with conventional triode tubes have been found to be as follows:

Resistor 13-20,000 ohms Resistor 14-10,000 ohms Resistor 2150,000 ohms Resistor 25150,000 ohms Capacitor 17-.00l microfarad Capacitor 18-.0005 microfarad The invention is only to be limited by the appended claims.

What is claimed is:

l. A pulse stretcher comprising, a phase splitter circuit, including an electron tube having anode, cathode,

and grid, resistors joining said anode and cathode with a source of plate potential and ground respectively, said anode resistor having a larger resistance than said cathode resistor, a pair of diodes having an anode and cathode of each joined together, a blocking condenser joining the free cathode of said pair of diodes with the plate of said electron tube, the free anode of said pair of diodes being connected with the cathode of said electron tube, a capacitor connecting the joined anode and cathode of said pair of diodes with ground, an amplifier circuit including an electron tube having anode, cathode and grid, resistors joining said last mentioned anode and cathode with a source of plate potential and ground respectively, said last mentioned grid being connected with the joined anode and cathode of said pair of diodes, a leakage resistor connecting said free cathode of said pair of diodes With the cathode of the electron tube in said amplifier circuit, and an adjustable tap on the anode resistor in said amplifier circuit, whereby the voltage variation at said tap will be dependent on the magnitude of the pulses applied at the grid of the electron tube in said phase splitter circuit.

2. A pulse stretcher comprising, a phase splitter circuit including an electron tube having anode, cathode and grid, resistors joining said anode and cathode with a source of anode potential and ground, respectively, said anode resistor having a larger resistance than said cathode resistor, a pair of diodes, the anode of one diode being connected to the cathode of the other diode of said pair, a condenser joining the free cathode of said pair of diodes with the anode of said electron tube, the free anode of said pair of diodes being connected with the cathode of said electron tube, a capacitor connecting the joined anode and cathode of said pair of diodes with ground, an amplifier circuit including electron tube having anode, cathode and grid, resistors joining said lastmentioned anode and cathode with a source of anode potential and ground, respectively, said last-mentioned grid being connected with the joined anode and cathode of said pair of diodes and a resistor connecting said free cathode of said pair of diodes with the cathode of the electron tube in said amplifier circuit.

3. A pulse stretcher comprising, means for producing a pair of simultaneously occurring pulses of equal time duration in response to a pulse applied thereto, said pair of pulses including a positive pulse having an amplitude proportional to the amplitude of said input pulse and a negative pulse, said positive and negative pulses appearing at first and second outputs of said pulse producing means respectively, a pair of rectifiers each having an anode and a cathode, the cathode of a first of said rectifiers being connected to the anode of a second of said rectifiers, means conductively connecting the anode of said first rectifier to said first output of said pulse producing means, a first capactior connecting said cathode of said second rectifier to said second output of said pulse producing means, a second capacitor connected between said cathode of said first rectifier and a point of fixed reference potential, an amplifier circuit including an electron tube having an anode, a cathode and a grid, resistors joining said last-mentioned anode and cathode with a source of anode potential and a point of fixed reference potential respectively, said grid being connected to the joined anode and cathode of said rectifiers, and a resistor connected at one end to said cathode of said electron tube and at the other end to the cathode of said second rectifier.

References Cited in the file of this patent UNITED STATES PATENTS