US2662981A - Wave form generating circuits - Google Patents

Description

Dec. 15, 1953 c. A. SEGERSTROM 2,662,981

WAVE FORM GENERATING CIRCUITS Filed Oct. 4, 1950 EMA/Avila PULSE 0077 07 Patented Dec. 15, 1953 WAVE FUR/M GENERATING CIRCUITS Carl A. Segerstrom, Winchester, Mass, assignor to Raytheon Manufacturing Company, Newton, Illa-es a corporation of Delaware Application Qctober 4, 1959, Serial No. 188,426

5 Claims.

Thi invention relates to wave form generating circuits, and more particularly to a circuit for producing a saw-tooth wave form.

It is well known that an extremely linear sawtoot-1 wave form may be produced by a vacuum tube circuit using the Miller effect. Such a circult must be periodically deenergiaed, switched, or gated to return the circuit to its starting condition.

This invention discloses a saw-tooth wave-form generating circuit which is self-switching, selftriggering, or oscillatory. Briefly, this is accomplished by placing a discharge device, shown here, byway of example, as a gaseous, gridcontrolled discharge device across the capaci-- tance which feeds the signal from the plate to the control grid of the vacuum tube. When the capacitance has charged to a predetermined point, the gaseous-discharge device fires, thereby discharging the capacitance and returning the circuit to its initial starting conditions.

This invention further discloses the use of a cathode follower connected in the circuit between the plate and the capacitance which feeds the control grid of the vacuum tube. If the output of the circuit is taken from the cathode of the cathode follower, the advantages inherent in the cathode follower action may be realized; namely, a match to a low impedance load may be produced, relatively large powers may be drawn from the output, and variations in the output load will not substantially change the linearity of the Miller integrating circuit, and will produce little or no disturbance therein.

In addition, since the cathode follower is in the negative feed-back circuit between the plate and grid of the vacuum tube, any non-linearities in the amplifying action of U138 cathode follower, due to its use over extremely large voltage ranges, will be substantially reduced by compensation through the negative feed-back circuit of the vacuum tube.

This invention further provides means whereby a pulse may be obtained during firing of the gaseous-discharge device for use, for example, in cathode-ray tube applications as a blanking signal, and, if desired, a trigger signal may be used to terminate the duration of the sweep. Also, the sweep rate may be made extremely slow, if desired, without destroying the linearity of the wave form.

Other and further advantages of this inven tion will become more apparent as the description thereof progresses, reference being had to the accompanying drawing, wherein the single figure illustrates a schematic diagram of a circuit embodying this invention.

Referring now to the drawing, there is shown a vacuum tube i, which is shown, by way of example, as a pentode having a cathode 2 which is connected to ground, a control grid 3, a screen grid l, a suppressor grid 5 which is also grounded, and a plate 5. Control grid 3 is connected through a resistor l to a source of potential, shown here, by way of example, as a variable tap t of potentiometer 9. One end of potentiometer 9 is connected to ground, and the other end thereof is connected through a resistor it to a source of negative potential. The screen grid 5 is connected through a resistor H to 33+, and through a resistor 52 to ground. The plate 5 is connected through a load resistor is to 13+, and to the grid i l of a cathode follower amplifier E5. The plate it of amplifier I5 is connected to 3+, and the cathode l'l thereof is connected through a load resistor it to ground. The cathode E! is also connected through a charging capacitance i to the grid 3 of the vacuum tube I. The terminal of capacitance 59-, which is connected to the grid 3 of tube I, is also connected to the cathode 2d of a grid-controllcd, gaseous-discharge device 2 l. The plate 22 of device 2i is connected to the terminal of capacitance it, which is also connected to the cathode ll of cathode follower it. The grid .23 of device 25 is connected to a variable tap 2:3 of a potentiometer 25. One end of potentiometer 25 is connected to ground through a resistor 27, and the other end thereof is connected through a resistor 135 to source of negative potential.

The operation of the device Will now be described. Assume the gaseous-discharge device 2! has just fired. The condenser l9 discharges rapidly through the gaseous-discharge device 2i until the potential diiference thereacross is sufficiently low to extinguish the discharge device 25. When the discharge device 2! becomes extinguished, the grid 23 thereof regains control and prevents firing of the discharge device.

Discharge of condenser it tends to drive grid 3 positive, causing tube 1 to conduct heavily and hence produce a high voltage drop across plate resistor 53, thereby driving grid i i of cathode follower i5 negative. Cathode ll thereof follows until it differs in potential from grid 3 by the voltage at which discharge device 2i becomes extinguished. As the condenser 58 begins to charge from the source of negative potential through the potentiometer 9 and resistor l to one side of the condenser, and from the other side of the condenser through the cathode follower amplifier IE to 13+, the grid 3 tends to go negative and, therefore, the voltage at plate rises, thereby raising the potential of cathode ii at substantially the same rate as the voltage across condenser it increases. The result is that the potential difference across the charging resistor T remains substantially constant, and hence the rate of current flow into condenser ill through resistor is substantially constant. As a result,

the voltage across condenser 49 rises at a substantially constant rate, thereby producing a substantially linear saw-tooth Wave .form.

Since the charging current through resistor I remains substantially constant, the potential difference between the cathode 29 and the gridiiilfi of the gaseous-discharge device 29 remains sulstantially constant. However, the potential difference between the plateEZ .andthccathode 26 of the gaseous-discharge device'ti increases "as the charge developed across condenser is increases until a point is reached where the grid loses control and the gaseous-discharge device 25 fires. This again discharges the condenser is, thereby terminating the generation of one "ofzthe next.

By adjusting the variable tap of poteniometcr E, the potential across the charging re- :sistor 'lmay be adjusted during the charging period, and hence the rate at which condenser is .is;charged may be adjusted. By adjusting the variable tap of potentiometer the point at which the discharge device it fires for a given setting of variable i3 be adjusted, thereby adjusting the amplitude of the sweep.

When the gaseous-discharge device 25 fires and discharges condenser lathe grid 3 moves positive, thus causing an increase in the screen current which flows through resistor i5, and thereby producing a negative excursion of screen grid 5. This negative Wave form may used a blanking pulse during the discharge of condenser it between sweeps, and may be applied, for era-- ample, to a cathode-ray tube which is utilizing the sav -tooth generator a horizontal or vcr tical deflection voltage source. if desired, trigger pulses may be applied to grid 23 to terminate the sweep at any desired time or periodicity.

It is to be clearly understood that the gaseousdischarge device 2! could be, for example, a simple gaseous diode instead oi a grid-controlled. devica'said gaseous diode firing when the potential across condenser it reached a predetermined value.

'While the signal output, as shown here, is taken from the cathode i? of the cathode-fob lower 55, it could, if desired, be taken from the sistances, could be used in various places throughout the :circuit, and the other species of the Miller integrating circuit could he used-in place of .the particular rrangement shown here. Therefore, it is desired that this invention be not limited to the particular details of the embodiment of the invention described herein, exceptas defined by the appended claims.

What claimed is:

1. A wave-iorrn generating circuit comprising an electron-discharge device having a cathode, a control grid, and a plate, a circuit connecting plate to said control grid for .ieedingsignals thereoetween comprising a capacitance,

means for discharging said capacitance comprising a gaseous electron-discharge device having a cathode, a grid, and a plate, the plate and catode of said gaseous eleetromdischarge device be. ing connected to opposite sides of said capacitance, and the grid of said gaseous electron-dischargedevice being connected to a control volt age source.

2. A wave-form generating circuit comprising an electron-discharge device having a cathode, a control grid, a screen grid, a suppressor grid connected to said cathode, and a plate, a circuit connecting said plate to said control grid for feeding signals therebetvveen comprising a capacitance, means connecting said screen to a :sourcehf potential through a load impedance, and.meansfor.dischargingsaid capacitance comprising a gaseous electron-discharge device.

-3. A wave-form generating circuit compris- ;ing .an electron-discharge devic having cathode, acontrol grid, a screen a suppressor grid connected tosald cathode, and a plate, a circuit connecting said plate to said control grid for feeding signals therebetween comprising a capacitance, means connecting said screen grid to a source of potential through a load impedance, means for discharging said capacitance comprising a gaseous electron-discharge device having a cathode, a grid, and a plate, theplate and cathode of said gaseous electron-discharge device being connected to opposite sides of said capacitance, and the grid of said gaseous electron-discharge device being connected to a control voltage source.

4. A Wave-form generating circuit comprising an electron-discharge device having a cathode, a control grid, a. screen grid a suppressor grid connected to said cathode, and a plate, a circuit connecting .said plateto said control grid comprising a capacitance, means for deriving a ,pulse from said-screen grid comprising means connecting said screen grid to a source of potential, means .ifo'r discharging said capacitance comprising a gaseous electron-discharge device having a cathode, a grid, and a plate, the plate and cathode of said gaseous electron-discharge device being connected to opposite sides or" said capacitance, and the grid .of said gaseous electron-discharge device being connected to a con trol voltage. source.

5. A waveeforin generating circuit comprising an electron-discharge device having a cathode, a controlgridanda plate, a circuit connecting saiolplate tosaid control grid for feeding signals therebetvveen comprising a capacitance, means for varying the'chargeon said capacitance C0111" prising a gaseous-discharge device, said gaseousdischarge device having a control electrode, and means forieeding signalpulses tosa d control electrodeto fire said discharge device.

CARL A. SEGERSTEOM.

References Uited'in'thefile of this patent UNITED STATES PATENTS Figs. 5-48 onpage. 1'99 and paragraphs 5.15-5.16 on pages -197 of Vol.19, published in 1948 by MCGIaW-Hill.

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