US2540923A

US2540923A - Electron-discharge tube circuit arrangement

Info

Publication number: US2540923A
Application number: US762373A
Authority: US
Inventors: Williams Frederic Calland
Original assignee: Individual
Current assignee: Individual
Priority date: 1944-10-02
Filing date: 1947-07-21
Publication date: 1951-02-06
Anticipated expiration: 1968-02-06
Also published as: FR962829A; BE478970A; GB583553A; CH268975A

Description

2 Sheets-Sheet l 2lI Cl. 5

F. C. WILLIAMS [nven W'LMM" 3y W 77] w-r? Attorney Ol dw Feb. 6, 1951 F, Q WILLIAMS 2,540,923

ELECTRON-DISCHARGE TUBE CIRCUIT ARRANGEMENT Filed July 21, 1947 2 Sheets-Sheet 2 t H.T.+

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RI R4 R5 C2 IW- Dl l VI (al R5 U R BT tl "P3 u gaz FIG. 4 P- F. c. williams Invemqr H.T.- By 4L h4 `'Patented Feb. 6, 1951 Emergenti-DISCHARGE `TUBE CIRCUIT ARRANGEMENT Frederic alllandhWilliams, Timperley, England Application :any 21; 194i, seiiai No, 762,373 In Great Britain october 2, 1944 secticni', rubiicnaw eemnugust s, 1946 Patent expires October 2, 1964 (Cl. RSU-127) i 12 Claims.

` This invention relates to!` electron-discharge tube circuit arrangements for use in producing waveforms showing desired characteristics and thewobject of the invention is to providel a circuit arrangement for. producing a sharp wavefront at a predetermined instant. p

According to the present invention a'circuit slrrangement for generating a voltage waveform having a` sharp wavefront at a desired `instant during the run-down of an alillid negative-@i113 voltage comprising an electron discharge tube, switch means such as a diode through which said voltage may b applied tdthe control grid of the tube at the desired instant as determinedby the instantaneous Value of said voltage and a regelrerative feedback circuit closed by the switch Ireajns,` the arrangement being such that if' the negative-going voltage is applied kvt/hen the tube isconducting then at' the desired instant boththe applied waveform and the feedback" become effective `in turning the t'ube on on its control grid thereby'generating the shar'pwavefront' in an outputcircuit of the tube. v A

Also according t the'prescnt invention, a circuit arrangement Iror producing a voltage "wave` form of desired timingv and' of sharp wavefront includes anV electron-'discharge'tube the control grid of which normally' takescurrentand'` a r'e! generative feedback circuit for controlling the potential of the control grid of the tub in such ajrnanner that thev application to ther grid of a negative-going voltage cuts off the grid current atan instant determined by `an initial negative potential effective'in' the feed-back circllit.n The feedback circuit may be connected between'the control grid; andanotherrlelegctrode of the` tube' andthe initial potential referred to maybe that applied to an electrode of a unilaterally conducting' device such as the anode of a diode inthe feedbackcircuit, to the cathode of `which the negative-goingvoltage is applied, the anode of the diode being coupled to the control grid of the electron dischargeV tube;

,In a particular circuit arrangement embodying theinvention thefeedback circuit is constituted by a` transformer coupling between the cathode of the tube and the control grid; thetransformer coupling being completed through a unilaterally conducting device such as a diode'an'd `through a coupling condenser, and the operation of the circuit is such that regeneration does not occur until the potentials applied to the unilaterally conducting device cause the feedback circuit to becomeeffective'.` I N In order that the invention may be more clear- 2. ly understood, and readily carried intoeffect, one circuit arranged to operate in accordance there: with will now be described by way ofexainple with reference to the accompanying drawing in which:

Fig, 1 shows such a circuit, Y,

Fig. 2 shows voltagewave forms associated with certain electrodes of the valves shown in Fig. 1, and

Figures 3 ande show m'odicaticns of the circuitA shownv in Figure 1.

The circuit of Figure 1 is intended t0 produce a wave form having an extremely sharp wavefrontor leading `edge whichrlis'tinied to occur at any controlled instant during the period of a sawtooth waveform. `It may lbeassunoed that there is` available at the input of the circuit shown in Fig. l a sawtooth voltage waveform as shown at a in Fig. 2 and that it is desired to produce a sharp wavefront at the instant `:c in thesawtooth cycle. The linear part of thesawtoothcoccurs during the period from t=0 to t'=T and it will be assumed that :n may have any' value `such that 0 is less than :c which in turn is'l'e'ss than T.

Referring to Fig. 1, the initial duiefscentl state of the circuit is such that the' control grid of a pentode valve Vl is taking current, the; anode current of the valvebeing at saturation level such that its voltage is at the lowest level.` The sawtooth voltage waveform 11 the D.AC. component of which is restored to ground level, is applied from terminal tl through the secondary winding of a pulse transformer PT to the cathode' of a diode valve DI. The potential of the anodeuof this diode is adjusted to a value -V by a'tapping o n a potentiometer resistance P connected to a source of 200 volts' negative, a resistance RZbeing connectedin" the lead to the anode of the diode.

If now the slope of the sawtcothis o volts per microsecond, that is to say the' waveform goes increasingly negative at the rate of c volts per microsecond, the cathode potential of the diode will become equal to the' anode potential after a period represented by :c microseconds where In the present instance,l for example, o= 4. When the instant :z: is reached the diode functions as a switch means andthe sawtoothvoltage is applied to the controlwgrid of tllevalVeVl` through the diodel the condenser Cl and theV resistance R3. The anode voltage of the diode now follows the curve shown at b` in Fig. 2` and the control grid potential is thus progressively decreased. The

3 cathode current of the valve VI is decreased and a negative-going wavefront is developed across the primary winding of the transformer PT, the primary winding of which consists of 135 turns of number 38 S. W. G. wire wound in one layer next to a core of radiometal. The secondary winding consists of 200 turns of similar wire wound on top of the primary winding and suitably insulated. The sudden variation in the primary winding is stepped up by the secondary windingand applied to the cathode of the diode DI and thence through the coupling condenser CI and resistance R3 to the control grid of the valve Vl This regenerative action results in the valve Vl being cut off due to feedback almost instantaneously thereby producing at the anode a positive-going voltage waveform with a sharp edge as shown by waveform c, Fig. 2, and a negative pip in the potential of its cathode as shown in waveform d in Fig. 2.

At the completion of a cycle of the sawtooth voltage waveform, the electrodes'of the diode DI and valve Vi return to their initial operating values and the circuit returns to its quiescent state. If the return time of the sawtooth waveform is short, and the condenser/resistance combination CI/R3 does not transfer the whole of the waveform to the control grid, the back edge of the square waveform c may not coincide with the return to quiescence of the waveform b.

In the particular circuit described the anode of the valve Vl is connected through its resistance R6 to a high tension source of 330 Volts positive and the control grid is connected through resistances R3 and RI to a source of 200 volts positive.

The resistances and condensers shown have the following values:

Resistances (k=1000)-- Rl= megohms R2=270 ohms R3=470 ohms R4=56lc ohms R5=33k ohms R6=1.51c ohms Condensers- C l :1000 micro-micro farads C2=0.1 micro-farad C3=0.1 micro-farad A suitable type of diode Dl for the circuit described is the Mullard type EA50 and the Valve Vl may be a Mullard type EFO. Clearly, other types of Valves with appropriate characteristics may be employed.

It will be understood that variation of the initial negative voltage applied to the anode of the diode Di and choice of a sawtooth waveform of appropriate. slope enables selection to be effected of the instant a: at which a sharp voltage wavefront may be developed at the anode of the valve VI and taken off from the condenser C2.

Again, since A. C. coupling to the control grid of the valve Vl is used, it will be seen that the applied sawtooth waveform may commence at a positive voltage if desired, the anode potential of the diode DI being adjusted to a smaller positive voltage. g

A desired modified anode waveform may be obtained by applying a modulation waveform of the suppressor grid of the pentode valve Vl. Thus, for example, if before the time t=0 in Fig. 2 a potential is applied to the suppressor grid such that anode current is cut-onc and then between the times t=0 and t=T the applied poten- 4 waveform c of Fig. 2 will be a negative square wave commencing at t=0 and ending at t=. It will be appreciated that the sharp wavefront occurs at t= and is the back edge of the negative wave. Y

Instead of connecting the primary winding of the transformer in the cathode lead of the valve VI as described, it may be connected in the anode lead. The square waveform output is in this case taken from the screen grid of .the valve Vl,A the remaining circuit connections and performance being similar to thecathode feedback case described. This modification is illustrated in Figure 3. Alternatively, the feedback connection may be taken from the screen grid of the valve VI, the output lbeing taken from the anode as in Fig. 1. This modification is illustrated in Figure 4.

I Claim:

1. A circuit arrangement for generating a voltage waveform having a sharp wave f ront at a desired instant during the run-down of an applied voltage comprising a diode to which said voltage is applied, biasing means for said diode for preventing conductionr through said diode until a predetermined time after the beginning of the run-down of said applied voltage, an electron discharge tube, means for applying a pulse to an electrode of Said electron discharge tube on the conduction of said diode to cause a change in the condition of said electron discharge tube, and regenerative feedback circuit including an amplifying device between another of the electrodes of said electron discharge tube and the inputof said diode, said feed-back circuit being completed on the conduction of said diode whereby a sharpV wave front is produced in the output circuit of said electron discharge tube. Y

2. A circuit arrangement as claimed in claim 1 wherein said regenerative feedback circuit comprises a step-up transformer the primary winding of which is connected in circuit with said electrode while the secondary winding is connected in series with the input circuit to said diode.

3. A circuit arrangement as claimed in claim 2 wherein said primary winding is connected in circuit with the cathode of said electron discharge tube.

4. A circuit arrangement for generating a voltage waveform having a sharp wave front at a desired instant during the run-down of a negativegoing voltage comprising a diode having Van anode, said diode having a cathode to which is applied said negative-going voltage, variable biassing means for applying a negative bias to the anode of said diode to prevent conduction of said diode until a predetermined time after the beginning of the run-down of said negative-going voltage, an electron discharge tube having an anode and a cathode as Well as a control grid, 9, power cir- I cuit for applying a direct current potential between said anode and said cathode with the latter negative, means for applying a positive bias to the control grid of said tube to cause the tube to conduct, an alternating current coupling cr-Y cuit having a short time constant between the anode of said diode and said control grid whereby on the conduction of said diode a negative-going pulse is applied to said control grid to initiate the cutting off of said tube, and a regenerative feedback circuit including a step-up transformer having its primary winding in series with said power circuit and its secondary winding in series with the cathode of said diode, said feedback circuit tial is raised to cause anode current to flow, the being energized on the conduction of said diode whereby said tube is sharply out off and a sharp Wave front is thus produced in the output circuit of said electron discharge tube.

5. A circuit arrangement as claimed in claim 4 wherein said regenerative feedback circuit is taken from the cathode and the output is taken from the anode of said electron discharge tube.

6. A circuit arrangement as claimed in claim 4 wherein said regenerative feedback circuit is taken from the anode and. the ,output is taken from the screen electrode of said electron discharge tube.

7. A circuit arrangement as claimed in claim 4 wherein said regenerative feedback circuit is taken from the screen electrode and the output is taken from the anode of said electron discharge tube.

8. In a circuit for producing a wave having a sharp Wave front, generator means for producing a linearly varying potential, said generator means including an output circuit, an electron discharge device having an anode as well as a cathode with a control grid between the anode and the cathode, a source of direct current potential having its positive side connected to said anode and its negative side connected to said cathode, means connecting the negative side of said output circuit to said grid and the positive side of said output circuit to said cathode, means in said output circuit for blocking passage of current therethrough to said grid when said rstnamed potential is below a predetermined value and for permitting passage of current to said grid in said output circuit when said first-named po tential is above said predetermined value, and means connected in series with said source of direct current potential for increasing the potential of said output circuit in response to a decrease in current iiow from said source.

9. In a circuit for producing a wave having a sharp Wave front, generator means for producing a linearly increasing potential, said generator means including an output circuit, a half wave rectier having its negative pole connected to the negative side of the output circuit, an electron discharge device having a cathode and an anode, said device also having a control grid, a feeder connection between said grid and the positive pole of said rectier, a direct current power supply, a circuit including electrical connections respectively connecting the positive side of said supply to said anode and the negative side of said supply to said cathode, a step-up transformer having a primary winding in series with the last-named circuit and a secondary winding in series with said output circuit, an electrical connection between the positive side of the output circuit and said cathode, and means for applying a potential between the positive pole of the rectier and the positive pole of the output circuit with the positive side of the last-named potential being applied to the rectier, the lastnamed potential having a value greater than the potential of the generator means at the beginning of variation of the latter potential and less than the potential of the generatormeans at the end of the linear variation of the latter potential.

l0. The system dened in claim 9 in which the feeder connection comprises in series, a condenser and a resistor, said condenser and resistor having such values of capacity and resistance respectively that the time constant of the circuit including them is short as compared with the time period elapsing between the beginning and the end of a single linear increase of potential of the generator means.

11. The system dened in claim l0 in which a rst side of the condenser is connected to said rectifier and a first side of the resistor is connected to said grid, and a source of direct current having a positive side connected to the second sides of said condenser and resistor and a negative side connected to said cathode, said lastnamed source applying suiiicient potential to said grid to effect saturation of the electron discharge device in absence of current flow through said rectifier.

l2. The system defined in claim 9 including in addition means to bias said grid positively to a sufficient degree to effect saturation of the electron discharge device in the absence of bias potential applied through said rectifier.

FREDERIC CALLAND WILLIAMS.

REFERECES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,230,926 Bingley Feb. 4, 1941 2,258,752 Fewings et al Oct. 14, 1941 2,266,509 Percival et al Dec. 16, 1941 2,414,486 Rieke Jan. 21, 1947 2,426,710 Sanders Sept. 2, 1947