US2370255A - Electron beam valve device - Google Patents

Description

Feb. 27, 1945. NAGY ETAL 2,370,255

ELECTRON BEAM VALVE DEVICE Filed June 16, 1942 2 Sheets-Sheet 1 Feb. 27, 1945. N-AGY ETAL 2,370,255

ELECTRON BEAM VALVE DEVICE Filed June 16, 1942 2 Sheets-Sheet 2 Patented Feb. 27, 1945 ELECTRON BEAM VALVE DEVICE Paul Nagy, Richmond, and Marcus James Goddard, Newbury, England Application June is, 1942, Serial No. 447,273 In Great Britain July 7, 1941 8 Claims.

The present invention relates to electronic valve circuits employing an electronic valve wherein an electron beam is focussed into an electron image on an electrode and wherein output signals are developed by deflection of the electron image across said electrode, during some part of which deflection the electron beam may partially or wholly leave the electrode.

Various forms of electronic valve have been described in which the output signals are thus produced by the deflection of an electron beam, but in all these forms the essential underlying principle is that the electron beam is deflected across a line of demarcation appertaining to the electrode upon which the electron beam is tocussed. This electrode will be hereinafter referred to as the output electrode. In some forms, a single homogeneous output electrode is employed. In such forms the line of demarcation is the edge of the electrode. In some forms two output electrodes are employed. .In such forms the line of demarcation is the line of separation of the two electrodes. In some forms one output electrode is employed which is divided into two parts or surface areas. This division may be.

eiiected by the shape of the electrode, or by a substance coating one part which has different electrical properties from those of the surface of the other part, or by an auxiliary electrode system fixed adjacent to the output electrode.

In such forms the line of demarcation is the line of division of the two parts.

In. each of these forms the output signals are produced by the oscillation of the electron beam across the line of demarcation under the influence of input signals, which are usually applied to a pair of electrostatic deflection plates. The efficiency of the valve depends on the smallness of the deflection of the electron beam necessary to produce signals of a given amplitude, since this controls the amplification produced by the valve. If the deflection necessary to produce output signals of the required amplitude. is very small then small changes in the location of the electron beam due toaccidental disturbances in the valve will cause intolerable disturbances in the output. For example, when the deflection sensitivity of the beam valve is high, minute changes of the bias potentials of the deflection plates can result in a displacement of the electron image which is of the order of the width of said electron image, and thus the image may be displaced right ofi the output electrode. In such a case the valve may stop functioning altogether. If. therefore, a high amplification is to be obtained, it is important that the effect of such accidental disturbances should be eliminated.

There is always an optimum mean position of the image. The present invention provides an electrical circuit whereby the eflect or accidental disturbances on the output is substantially eliminated, and wherebythe image automatically is kept substantially in this optimum mean positlon, and the invention consists, in general, of an electrical circuit including an electronic valve device containing means for producing an electron beam and deflection means to which electric signals may be applied in order to deflect said electron beam, wherein means are provided for feeding on to said deflection means an electrical signal produced. by said electron beam on an electrode of said electronic valve device due to any disturbance which tends to deflect said electron beam, whereby the deflection of the electron beam which said disturbance tends to produce is substantially eliminated.

In the operation of the invention a signal produced by; the displacement of the electron "beam due to an accidental disturbance is fed on to a deflection plate of the valve in such a way that the displacementof the electron beam is counteracted or reduced, thereby reducing the disturbance produced in the output.

The signal which is thus fed back may be derived from the output electrode or it may be produced on an auxiliary electrode adjacentto the output electrode. In either case it is .fed on to the afore-mentioned plate of the valve through any convenient impedance which impedance may be part of an impedance bridge through which the potential of the deflection plate .is defined.

Although the amplification of the valve has been stressed herein, the invention .is nevertheless not confined to use in connection with a valve employed as an amplifier. It is applicable to the type of valve described iffit is, desired to eliminate the efiects of accidental disturbances when the valve is applied to other purposes, e. g.

normal output signals.

In certain adaptationsoi the beam valve, for

instance as a detector, arrangements may advantageously be made whereby the width of the electron image is automatically controlled to a desired value. The relative ratio of the first and second anode potentials of the focussing system of the electron beam may be automatically adjusted by signals developed on one or more of the electrodes of the beam valve.

Reference will now be made to Figure l, which shows a high frequency amplifier circuit including a deflection modulated cathode ray valve I of the type described in our United States application S. No. 403,914, filed July'24, 1941, Patent No. 2,313,886, dated March 16, 1943. Signals to be amplified. are fed through a tuned circuit H on to a deflection plate 12 of the valve H1. The potential variations thusproduced on the deflection plate 12 cause an electron beam, produced by a cathode [3, a grid 14, and a first anode l5, and focussed by a second anode IE on to an output electrode IT, to oscillate across the output electrode [1, thereby producing output signals across the output impedance 18. The output electrode I1 is of the type which is divided into two parts. A suppressor grid lies adjacent the part He, and is maintained at a potential negative rela tive to the output electrode, so that when the electron beam falls on the part Ila, all secondary electrons are suppressed, and the output electrode is charged in a negative sense. Adjacent the part 11b is a grid 2| which is maintained at a potential positive relative to the output elec trode, so that when the electron beam falls on the part l'ib the secondary electrons are collected by'the grid 2|, and the output electrode is charged'in a positive sense. A more detailed description of the operation of this output electrode will be found in the afore-mentioned United States application S. No. 403,914.

When the electron beam falls partly on the part 11a and partly on the partv l'lb, the rate of charging of the output electrode is the resultant of the rate of negative charging of the part Ila and the rate of positive charging of the part Nb, and may be either positive or negative or zero. For the circuit of Figure l, the optimum mean position of the electron image on the output electrode is that which correspond to .zero charging of the output electrode.

" The automatic control of the position of the electron beam is afforded by the resistance l9.

:This is the simplest form which the automatic control according to the present invention can take. This resistance l9 connects the output impedance l8 to the potential tap of the second anode l6, while the output impedance is also connected through the resistance 23 to the deflection plate I2. .The A. C.'signals produced in the impedance l8 are decoupled to earth through the decoupling condenser 22, so that only D. C. signals and signals of relatively low frequency from the output electrode pass through the resistances l9 and 23. The condenser 22 also decouples any input signals ,which pass through the resistance 23. When the electron beam falls in the optimum mean position,- there is no D. C.

I the disturbance.

signal on the output electrode. tential of the deflection plate [2 and the mean potential of the output electrode I! are second anode potential.

If, however, the electron beam becomes disof potential, is communicatedto the deflection plate l2 through the resistance 23, which should be much higher than the impedance of the cir- "cuit H, and this deflects the electron beam back towards the optimum mean position, thereby sub-, stantially eliminating the displacement due to If the displacement is towards the positive part Ilb of the output electrode, the output electrode becomes charged in a positive sense,and the change of potential thu produced is communicated to the deflection plate [2, there by deflecting the beam back towards the optimum mean position as before. I I

The actual resulting displacement andchange of potential of the output electrode may readily be calculated. For example, suppose the beam current of the electron beam is ib, and that the current falling on the positive part 11b of the output electrode is multiplied by secondary emission by a factor 1,0, while that falling on. the negative part Ila is multipliedby a factor (p. Let the deflection sensitivity of the deflection plate l2 on the electron beam be denoted by Ds, and suppose the disturbance causing the displacement of the electron beam corresponds to a displacement y of the beam. Denote the resulting displacement of the beam by A, and the change of potential of the output electrod by v. Let the width of the electron image be denoted by 2a and the value of the resistance l9 by R. The displacement A is the resultant of the displacement y and the counter-displacement produced by the change of potential v communicated to the deflection plate l2. This counter-displacement is v.Ds. Thus:

A==yv.Ds (l) The displacement A causes a current to flow to the output electrode of which the magnitude is: ib.( +1//).A/2a. The change of potential 12 thus produced across the resistance R. is given by:

v=R.ib.(+ .A/2a (2) Substituting this value in (l) and transforming,

we obtain:

1+Ds.R.ib.(+i//)/2a l+ R where ,u is the mutual conductance of the valve. Hence, from (2):

Thus the po- 7 Thus the resulting displacement is only 1/150,0U0 of the magnitude than it would be if the automatic image control were not employed. Also, if the disturbance corresponds to a displacement y of 5 times the image width, i. e. 1 mm. in the'abo've example, then the change in the .mean potential of the output electrode is v=0.2 volt, which is quite unimportant.

' In Figure 1 the earth point is shown as being the point to which the grid I4 is connected, but this is unimportant; any of the electrodes l3, l4, 1'5, l6 could be chosenas the earth point.

It should also be noted that the second anode I6 is shown connected to a less positive potential than the first anode It; This procedure is not essential, but has nevertheless certain advantages. In the first place the less positive potential of the second anode, which is equal or very nearly equal to the potential of the deflection plate l2, gives greater deflection sensitivity to the deflection plate. Also in the circuit of Figure 1 the output electrode is connected to second anode potential. The grid 2| must be more positive than the output electrode, and it is economical to connect the first anode also tothis more positwo potential. Furthermore the use of the most positive available potential for the first anode produces the minimum of aberrations in the electron image formed by the electron beam.

It has been assumed above that the optimum mean position of the electron beam corresponds to the position of zero charging of the output electrade. This assumption requires some further comment.

The mean position of the electron beam can be changed without aiiec'ting the amplification of the valve. The input acceptance of the valve is actually greatest if the centre of the beam falls on the line of separation of the positive .and negative parts of the output electrode in the mean position; this only corresponds to the position of zero charging if 4: and l are equal. If, however, the beam is adjusted to some mean position which does not correspond to the position of zero charging, then a D. '0. current flows permanently to or from the output electrode through the resistance 19. This produces a potential difierence across the resistance 1 9, and this resistancemust 'be connected to a potential difiering from second anode potential'by an amount equal to the aforesaid potentialdifierence in order that the deflection" plate |2 shall be on second anode potential. This fact is of no consequence, apart from considerations regarding simplicity of the circuit, if the beam current ib is constant during operation of the valve, but if the beam current is altered by adjusting the volume control, then the current in the resistance l9 also changes, therebychanging the potential difference across the resistance. This change in the potential diiference must be compensated either by changing the value of the resistance |9 suitably or by adjusting the potential tapping to which it is connected. This additional adjustment i most undesirable.

It should .be noted that, in the circuit of Figure 1, no preliminary adjustment of the automatic control circuit is necessary. The electron beam is automatically set to the optimum mean position when the valve is switched on.

Figure 2 shows an audio frequency amplifier circuitincluding a deflection modulated cathode ray valvev 25 of the type described in our co pending patent application Ser. No. 447,277. In

common with the circuit of Figure 1 input siz nals in the circuit 'of Figure 2 are applied to a deflection plate l2 of the valve, wherein an I electron beam is generated and focussed by a cathode l3, grid M, first anode |5, and second anode 5 which function in the same way as the electrodes similarly numbered in Figure "The input impedance, across which the input signals are produced, is in Figure 2, however, a resistance 26, and the output signals are likewis developed across a resistance 21. The output electrocle 29, from which the output signals are :obtained, is of thesingle homogeneous type. The secondary electrons emitted from the output eieo trode 29 under the influence of the electron beam are collected by a grid 2|, which is maintained at a potential more positive than the output electrode. The output electrode is always charged in one sense only by the electron beam, positive if its secondary emission coefficient is greater than unity and negative if its secondary emission coefiicient is less than unity. In what follows it will be assumed that the secondary emission coeflicient is greater than unity, but conditions are exactly the same in principle if the secondary emission coeflicient is less than unity. Automatic control of the electron image according to the invention is effected by means of'the resistances 23, 30 and 3|. signals and signals of relatively low frequency produced on the outputelectrode 29 pass through these resistances, the A. C. signals corresponding to the input signals being decoupled through the decoupling condenser 22. Any input signals mentioned patent application.

which pass through the resistance 23 are decoupled by the decoupling condenser 28. g

The output A. C. signals are produced from the output electrode 29 by oscillation of the elec-'- tron beam across the edge of the output electrode, thereby varying the amount of current passing from the output electrode 29 through the output resistance 21. A more complete description of the action of the output electrode system is given in the specification of the afore- The optimum mean position about which the electron beam should oscillate is that position in which half the electron beam falls on the output electrode. Thus there is a permanent D. 0. current passing to the output electrode. This current passes through the output resistance 21 and the resistance system 3|, 30, to the supply potentiometer 32, and, when the electron beamialls in the optimum mean position, the magnitude of this D. C. current is: i29=/z tbsp, where vzb is the electron beam current and l/ is themultiplication factor produced by secondary emission pro.- duced by the output electrode 29. The mean potential of the output electrode is defined relative to the point G of the potentiometer 3|, 30, which connects the points A and H of the supply potentiometer 32, by the magnitude of. the current 2'29 and the value of the resistance .21. The potential of the point G is in turn determined by the potentials of the points A and H,

the values of the resistances 30 and 3|, and the magnitude of the current 229 flowing through theresistance system 3|, 30. The mean potential of the output electrode may be set at a convenient value by adjusting the -tapping point A on the supply potentiometer 32. The point B of the potentiometer 3|, 30 is connected'through the resistance 23 to the deflection plate 12, .so

that the. deflection plate l2 acquires the potential of the point B. In the optimum working Only the D. C.

thence to the deflection plate l2. This more positive potential on the deflection plate pulls the electron beam back towards the optimum mean position, thereby substantially eliminating the effect of the disturbance. The change in the mean potential of the output electrode is quite unimportant, being of the order of one volt.

It may be shown that the resulting displace-1 ment A caused by a disturbance corresponding to a displacement y of the beam is given by:

y 1+,J2B 1+R30 R31 where #:Dsib tD/Za is the mutual conductance of the valve, and RB, R30, R3l are respectively the resistance between Band H, the value of the resistance 30, and the value of .the resistance 3|. The change of potential v of the output electrode is given by:

1 y. .R30.(l+R27/R30+R27/R31) Ds. 1+R3o R31+,..RB where R21 is the value of the resistance 21. for example we take:

Ds=5 mm./volt. ib=0.2 milliamps. 0.2 mm.

y=1.0 mm. RB=100,000 ohms. R27=300,000 ohms. R30=400,000 ohms. R31=1,600,000 ohms.

then we obtain: A =:l//2,000

12:1.55 volts.

The operation of the automatic beam control device is the same apart from the sense of the deflection and potential changes if the disturbance causes the electron beam to be displaced further oil the output electrode.

If the circuit of Figure 2 is employed in the audio frequency range, it is desirable that the decoupling condenser 22 should have a-low im- I p'edance above 50 cycles/sec. and a high impedance below 50 cycles/sec. Thus it may conveniently be replaced by a high-pass filter with a cut-cit just above 50 cycles/sec. In order to counteract any microphony in the valve, it is possible to place an additional tuned circuit in series with 22 which is tuned to the microphonic frequency, so that this frequency is not decoupled but is fed through the automatic beam control system. Signals of this microphonic frequency produced on the output electrode 29 are thereby counteracted, so that the eiTect of the microphony is substantially eliminated.

Figure 3 shows a high frequency amplifier circuit. including a deflection modulated cathode ray valve 33 of the type described in our co-pending application. The output electrode 34 is of the single homogeneous type, but, in contradistinction to the output electrode 29 in Figure 2', it is adapted to be charged in a positive sense by secondary emission from itself or in a negative sense by secondary emission from an auxiliary electrode 35. A more complete description of the operation of this output electrode system is given in the specification of the aforesaid application.

The circuit of Figure 3 is the same as that of Figure 1 in all essential particulars, except that the resistance l9 which afiords the automatic beam control according t the present invention is not connected to the output impedance I8, but instead is connected to an auxiliary electrode 36. When the electron beam falls in the optimum mean position, this electrode 36 intercepts a fraction of the beam current. Advantageously one edge of the electrode 36 coincides with the centre of the electron beam when the beam is in the optimum mean position. The fraction of the beam current intercepted by the electrode 36 causes a current to flow in the resistance I9, therebyestablishing a potential diiference across the resistance I9. Thetapping J at which this resistance is connected to the supply potentiometer 32 should be so adjusted that the resulting potential supplied to the deflection plate I2, when the electron beam is in the optimum mean position, is second anode potential. If, now, a disturbance deflects the beam from the optimum mean position, the current reaching the electrode 36 changes, thereby causing the potential difference across the resistance l9 to change. The potential supplied to the deflection plate 12 is thus changed in such a way that the effect of the disturbance is substantially eliminated.

In the circuit of Figure 3, the automatic beam control isindependent of the output impedance, so that themean potential of the output electrode can beset at any desired value, by adjusting the tapping K at which the output impedance is connected to the supply potentiometer 32, without reference to the potentials required by the automatic beam control system. The independence of the automatic beam control and the output impedance has the further advantage that, since the resistance IS in the automatic beam control circuit is independent of the output impedance, the beam current employed is not limited by the requirements of the automatic beam control system, as it is, for example, in the circuit of Figure 2, where the resistances 3|, 30 of the auto- 'beam control system.

The circuit of Figure 3 is particularly suitable for use where the output impedance l8 consists of a pure capacity, as, for example, when the circuit is used as a Kerr cell amplifier.

The automatic beam control circuits shown in Figures 1 to 3 are described by way of example only, and the invention is not restricted to the exact form of circuits there shown. Also the circuit shown in connection with any one output electrode system is not applicable only to that output electrode system, nor does any one output electrode system require to be operated with the type of circuit shown in conjunction therewith.

For example, the automatic beam control circuit shown in Figure 1 is applicable without modiflcation to the output electrode ssytem shown in Figure 3. v

In the circuits of Figures 1 to 3, the automatic beam control has been shown operating with the aid of an electrostatic deflection plate. This deflection plate can be replaced by an electromagnetic deflection coil if desired.

What We claim and desire to secure by Letters Patent is:

1. In an electrical circuit, the combination with a multiple electrode electronic valve device including electrode means for producing an electron beam, and deflection means to which alternating current electric signals may be applied in order to deflect said electron beams of frequency selective means for feeding on to said deflection means an electrical potential produced by said electron beam on an electrode of said electronic device due to a disturbance of other than signal frequency which tends to deflect said electron beam, whereby the undesired deflection of the electron beam which said disturbance tends to produce ma be substantially eliminated.

2. In an electrical circuit, the combination with an electronic valve device, an input circuit upon which electric signals may be impressed, an output circuit, said electronic valve device including means for producing an electron beam and deflection means connected to said input circuit for deflecting the beam with respect to output electrode means to which said output circuit is connected; of means for suppressing inadvertent deflection of the beam by disturbances of non-signal frequency; said last means including a network in said output circuit for feeding to said deflecting means in degenerative sense the components of the output circuit potential variations of non-signal frequency. I

3; In an electrical circuit, the invention as recited in claim 2, wherein said output electrode means comprises an output electrode, said output circuit being connected-to said output electrode.

4. In an electrical circuit, the invention as recited in claim 2, wherein said output electrode means comprises an output electrode and an auxiliary electrode, and said output circuit includes an output impedance connected to said output electrode, said network being connected to said auxiliary electrode.

5. In an electrical circuit, the combination with an electronic valve device including means for producing an electron beam and deflection including resistance means connecting said output impedance to said source of energizing potential, and circuit connections between said resistance means and said deflection means to impose in degenerative sense upon said deflection means potentials of non-signal frequency developed across said resistance means.

6. In an electrical circuit, the combination with an electronic valve device including means for producing an electron beam, an output electrode, means including an anode for focusing the beam in the region of the output electrode by applying to said anode a direct current potential, and an electrostatic deflection plate on which the energizing potential during operation of the device is substantially equal to the potential of the anode, of an output impedance across which output signals may be produced in response to input signals applied to said deflection plate, a resistance network including a resistance connecting said output impedance to said anode and a second resistance connecting said output impedance to said deflection plate, so that any disturbance of non-signal frequency which tends to deflect said electron beam produces across said first resistance an electric potential which is fed through said second resistance on to said deflection plate, thereby substantially eliminating the deflection of the electron beam which the disturbance tends to produce.

7. In an electrical circuit, the invention as recited in claim 6, wherein said resistance network is connected to earth through a decoupling condenser so that feed-back of potentials of input signal frequencies to said deflection plate MARCUS JAMES GODDARD.

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