US2509065A - Electron discharge apparatus - Google Patents

Description

May 23, 1950 w. E. KIRKPATRICK 2,509,065

ELECTRON DISCHARGE APPARATUS Filed Dec. 22, 1947 T0 CATHODE/z y v To CoA/rem ELEcrko0E/4 Patented May 23, 195i() iJNsI'lED S'E'Aii' QFTET @FFME ELECTRON DISCHARGE APPARATUS Wiiiiam E. Kirkpatrick. Chatham, N- L assignr to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of NewYork Application December 22, 1947, Serial No. 793,071

(Cl. S15-fla) 9 Claims.

This invention relates to electron discharge apparatus and more particularly to energizing circuits for electron guns such as are utilized in cathode ray devices.

Electron guns of one known type comprise, V,in generaLa cathode, an .anode in association with .the .cathode `for accelerating .the electrons einanating from the cathode, away therefrom, and a controlelectrode for controlling the intensity of the electron beam projected by the gun. It desirable, Vfrom thestandpoint of convenience and ofsimplicity of Ycircuit.,design, that the controland accelerating .electrodes beenergized from a com- V.mon directcurrent source. However, in such gases ,variations of the potential applied to the electrodes Ydue to periodic or transient disturbances may vresult iin substantial variations in the beam ,intensity .inasmuch as'the beam intensityor current ,is dependent .upon the potential upon both Vthe control and vaccelerating electrodes. Such variations in beam current are highly objectionable in many cathode ray devices.

One general object of this invention is to improveenergizing or biasing circuits for .electron guns. More specicallyone object .of this inventicn is to reduce or substantially eliminate variations inthe beamintensity with changes or fluctuations `in the voltage supplied from a com- Ymonbiasing source yfor the control and accelerating electrodes v`of an electron gun.

,In accordance with one ieature of this invention,.the energizing circuit for biasing the gun .electrodes from a common source is constructed .as a network ,including a resistance-capacitance portion, such that .the control electrode bias is ,regulated to counter v balance changes in the beam current due to variations in the anode potential Whcrtcbygthe Vbeam intensity is maintained .substantially constant despite variations Lin the ,supply voltaea The invention and the above-noted andcther features thereof will -be understood more clearly `and fully `from the following detailed description with reference to v.the `aisonflparl.vine drawingk in which:

Figs. 1 `and 2 are circuit diagrams V,showing two illustrative embodiments Wof thisv invention,

-and

Fiaisra diagram which will ,be referred t vlclereinazftenin the .explanation of certain principles involved `in the circuits YofY Figs.'1 Aand 2.

Referringnow to the drawing, :the embodiment illustrated in Fig. 1 comprises a cathode ray device including an evacuated enclosingvvessel IB havving anw-output anode or target Il .at one-.end and anelectron gun at theother end, for projecting a 1concentratedelectron stream or beam to the outputanode. The electron gun comprises a cathode I 2, which may be ofthe indirectly heated type including a heater element I3, a control electrode or grid Id, for example in the form of la centrally apertured disc axially aligned with the cathode, and a focussing electrode I5, which also may be a centrally apertured disc axially aligned with the cathode. The gun includes also an accelerating anode axially aligned with the cathode and comprising, for example, Ya cylindrical portion I6 between the control and focussing electrodes and a centrally apertured disc Il between the'focussing electrode yand output anode and adjacent the former. The two portions IE and Il of the accelerating anodes are connected .t0- gether to Abe electrically integral, as shown.

"Ihe ,electrodes of the gun are biased relative tolone vanother -from a direct current source I8, v such as'.. a battery or rectifier, which is connected facross a pair of potentiometer resistors I3 and 42i) in series. As `illustrated in Fig. 1, the cathode J2 is connected directly to the common terminal of the vresistors I9`Aand20, the anode I6,.Il is connected to the positive terminal of the resistor I9, the focussing electrode is connected to an intermediatef'po'ntonthis resistor I9 and the control .electrode Ig is connected, through a resistor 2`I, to an intermediate point on the Yresistor 20. The relative potentialsofthe electrodes Iii .to'. I1 are made suchasto produce aconcentrated beam of prescribed intensity, projected toward the target "Il, It is .apparent that the anode I6, I'I is biased positive relative tothe cathode I2, Whereas Vthe controlelectrode 'It is biased negative relative; to the cathode. 'Y l Any variation in the voltage .supplied fromthe the control electrode .lli `and the anode l, il. `Both of these electrodes affect thebeam intensit,7

landchanges inthe bias tend to change the beam current diierentlybothin sense and magnitude.

For 'Lezainple,if the volta'getoithe source I Slincreases the vanooleabias increases, i. e..becomes more `positive and, thus, tends to increasefthe .beam current, Whereas the. bias uponcontrol electrode Iincreases, i. e. .becomes more negative, and hence tends to decreaserthe beam current.

Because of the diierences in the current-voltage .relations for the cathode-control .electrode and cathode-anode, the-variations in beam lcurrent due. to changes in the bias onthecontrolelectrode and ,anode are different inmagnitude as .well as insign. The relationof the .current variations which would result from change in the voltage of the source will be understood from the following analysis with reference to Fig. 3.

Fig. 3 is the alternating current form of the biasing circuit illustrated in Fig. 1. As indicated in Fig. 3, a change, AVs, of pulse or periodic form in the voltage from the source I8, due, for example, to a disturbing source, results in a change AVA in the bias of anode I6, Il and of aAVg in the bias upon the control electrode I4. The change in the anode bias will tend to produce a change in beam current of lciAVA and the change in control electrode bias will tend to produce a change in beam current of aczAVg, where Ici and k2 are constants, specifically the slopes of the current-voltage characteristics of the cathode and anode, and cathode and control electrode respectively, at the operating point. As pointed out heretofore, the two current changes are of opposite sign. Y

If the net change in beam current is to be Zero for a change AVs in source voltage, it is evident that the two current changes above noted must be equal. This will obtain if as is clear from Fig. 3 and noting that AVFAVSQZ.)

The condition requisite for zero net change in beam current with variations in the supply voltage can be obtained independently of any particular relation between the direct current biases for the anode and control electrodes. That is to say, the energizing circuit can be constructed so that the requisite or desired direct current biases can be set independently of the adjustment of the alternating current impedances to realize zero net beam current change with variations in the source voltage. One manner of effecting the alternating current circuit adjustment to obtain the zero net change in beam current desired is illustrated in Fig. 1.

The desired direct current operating biases for the anode I6, il and control electrode I4 are set by the resistors I9 and 20. The network for effecting the alternating current adjustment of the energizing circuit comprises the resistor 22 and condenser 23 in series and bridged across the resistor 20, and a second condenser 24 connected between the control electrode lll and an adjustable tap 25 on the resistor 22. rIhe resistor 22 corresponds to the impedance Ze in Fig. 3 and the resistor I9 corresponds to the impedance ZA in Fig. 3. The condenser 23 serves as a blocking condenser to keep direct current from the resistor 22 and is constructed to have a reactance small compared to Zg at the lowest frequency of variation in source voltage for which no change in beam current is to obtain. The condenser 24 also serves as a blocking condenser and is constructed to have -a small reactance compared to the impedance between cathode I2 and control electrode I4, looking into the cathode ray device. The resistor 20 has a resistance very small in comparison to that of resistor 22. Resistor 2I is large and prevents shunting of the adjustable tap 25.

In practice, the tap on the resistor 20 is set and so that the desired beam current ows to the output electrode or target Il. A voltage of the lowest frequency of disturbance likely to be encountered in the operation of the drive is irnpressed across source I8 and the tap 25 then is adjusted until no change from the desired value occurs in the current to the target III.

In a specific embodiment of this invention, the energizing circuit constants for an electron gun for producing a beam current of the order of 25 milliamperes with a control electrode bias of -50 volts and an anode bias of 1000 volts, the cathode to control electrode impedance looking into the device being many megohms, found satisfactory to result in no change in beam current for source voltage fluctuations of frequencies down to 60 cycles-per second were:

Iii-200,000 ohms 20--40,000 ohms Resistor 2I-1.0 megohm Resistor 21E- 400,000 ohms Condensers 23 and 24-1 microfarad The parameters k1 and k2 in the analysis presented above may vary for different potentials upon the control electrode and anode. Hence, exact balance of the current modulations due to changes in the voltages on these two electrodes will obtain only for relatively small changes in supply voltage. However, even for relatively large variations in this voltage, substantial balancing is realized with consequent substantial reduction in change in the beam current.

In the embodiment of the invention illustrated in Fig. 2, the focussing electrode I5 and anode I6, I'l are biased by way of the resistor I9, as in the embodiment illustrated in Fig. 1, and the control electrode I4 is biased by way of an adjustable tap 26 on the resistor 20. A condenser 21 is con- Resistor Resistor nected between a second adjustable tap 28 on the resistor 2i) and the common terminal of resistors I9 and 20. The resistor I9 corresponds to ZA in Fig. 3 and the resistor 20 corresponds to Zg.

The tap 26 is set to provide the desired bias and, hence, the desired beam current. The tap 28 is adjusted to realize the balance of beam current modulations due to disturbances in the supply voltage and, hence, in the potentials of the control electrode and anode. By an analysis similar to that followed hereinabove on the discussion of Fig. 1, it can be shown readily that if condenser 21 is sumciently large to act as a short circuit at the lowest frequency for which balance is desired, for the circuit illustrated in Fig. 2 the condition requisite for balance is where Ici, k2 are as discussed before, RA and Rg are the resistors I9 and 20, respectively, a is the proportion of the resistor 20 between the taps 26 and 28, yand is'the proportion of the resistor 20 between the negative terminal thereof and the tap 28. A change of AVs in the source voltage results in a change AVA in the potential of anode it Il and a change of AVg across the portion Rg of resistor 20.

Although specific embodiments of the invention have been shown and described, it will be understood that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as dened in the appended claims.

What is claimed is:

l.V Electron discharge apparatus comprising an electrongun including a cathode, a control elec- *estesa trode and an anode, means for biasing said control electrode and anode relative to said cathode comprising a resistance and a direct current source connected lacross said'resistance, a direct current connection .from said cathode to an intermediate point on said resistance, a direct current connection from said anode to a point on said resistance positive with Yrespect to Said intermediate point, a direct current connection from said control 'electrode to a point on said resistance negative with respect to said intermediate point, and means for controlling thepotential of saidcontrol electrode in accordance with variations on the voltage across said resistance, said controlling means comprising a condenser and resistor in series between said cathode and a point on said resistance more negative than that to which said control electrode is connected and a condenser connected between said resistor and said control electrode.

2. Electron discharge apparatus comprising an electron gun including a cathode, an anode and a control electrode, means for biasing said anode and control electrode `relative to said cathode including a iirst and a second resistor connected in series, a source for impressing a direct current voltage across said resistors and having its positive pole connected to said first resistor, a direct current connection from said cathode to the common terminal of said resistors, a direct current connection from said first resistor to Said anode and a direct current connection from a first point on said second resistor to said control electrode, and means for regulating the potential or said control electrode in accordance with Variations in said direct current voltage to maintain the current projected by said gun substantially constant, said regulating means comprising a condenser bridged between said common terminal and a point on said second resistor less negative than said rst point.

3. In combination, an electron gun comprising a cathode, a control electrode and an anode, a direct current voltage divider having a rst portion and a second portion, a direct current source for impressing a voltage across said portions and having its positive terminal connected to said first portion and its negative terminal connected to said second portion, a direct current connection between said cathode and a point between said first and second portions, a condenser and a resistor connected in series relation across said second portion with said condenser toward the cathode end of said second portion, said condenser having a reactance small in comparison to the impedance of said resistor at a preassigned frequency and said resistor being large in comparison to the resistance of said second portion, a resistive connection between said control electrode and said second portion, a capacitive connection between said resistor and said control electrode and having reactance small in coriparison to the impedance between said cathode and said control electrode, and a direct current connection between said anode and said iirst portion.

e. In combination, an electron gun comprising a cathode, a control electrode and an anode, a direct current voltage divider having a rst portion connected between said cathode and said anode and having a second portion in series with said first portion, a condenser and a resistance connected in series across said second portion with said condenser connected to the end thereof toward said rst portion, means for impressing a direct current voltage across ysaid voltage divider, a direct `current connection between said control electrode and said second portion, and a capacitive connection between said control electrode and a point on said resistance suchthat where k1 and k2 are respectively the slopes of the cathode-'anode and cathode-control `electrode characteristics, ZA 'is the impedance of said first portion, Zg is the impedance of said resistance and ais the portion of said resistance connected between said cathode and said control electrode, said second portion being of impedance small 'in comparison to said resistance.

5. Incombination, an electron gun comprising a cathode, a control electrode and an anode, ra direct current voltage divider having a'rst resistive portion connected between said cathode and said anode and having a, second resistive porion in series with said iirst portion, a source vfor impressing a supply voltage across said portions in series, a direct current connection bet-Ween sai-d control elect ode'and a iirst point in said second portion, and a condenser bridged between said cathode and a secondpoint on said second portion between said first point and said first portion and such that where k1 and k2 are respectively the slope of the cathode-anode and cathode-control electrode characteristics, RA is the resistance of said rst portion, Rg is the resistance of said second portion, a is the proportion of said second portion between said rst and second points and is the proportion of said second portion between said second point and said course.

6. In combination, an electron gun comprising a cathode and a pair of electrodes in juxtaposition thereto, each of said electrodes aiecting the intensity of the current projected by said gun in accordance with the potential of the electrode, and means including a source of direct current voltage for biasing said cathode and said electrodes, said means being subject to spurious variations which superimpose an alternating current voltage component upon the direct current voltage, said means including a rst adjustable direct-current connection between said source and said electron gun for controlling said direct current voltage bias between one of said electrodes and said cathode and a second adjustable alterhating-current connection between said source and said electron gun for controlling the bias component between said one electrode and said cathode due to said superimposed voltage components.

7. In combination, an electron gun comprising a cathode, a control electrode and an anode, and means including a source of direct current voltage and superimposed alternating current voltage for biasing said cathode, said control electrode and said anode, said means including a iirst adjustable direct-current connection between said electron gun and said source for controlling said direct voltage bias between said control electrode and said cathode and a second adjustable alternating-current connection between said electron gun and said source for controlling said superimposed alternating Voltage bias between said control electrode and said cathode.

8. Electron discharge apparatus comprising an electron gun including a cathode, a, control electrode and an anode, means for biasing said control electrode and `said anode relative to said cathode including a vvoltage divider, means for impressing a supply voltage across said divider, means for imposing a direct-current bias upon said control electrode and said anode relative to said cathode including direct-current connections from spaced points on said divider to said cathode, .control electrode and anode respectively, and means for impressing an alternating-current Voltage between said control electrode and said cathode to control the potential of said control electrode in accordance with variations in said supply Voltage to maintain the current projected by Aintensity of the current projected by said gun in accordance with the potential of the electrode, means for biasing one of said electrodes positive with respect to said cathode and the other of said electrodes negative with respect to said cathode, said biasing means including a voltage divider, means for impressing a voltage across said divider, direct-current connections from said cathode and each of said electrodes to spa-ced points on said voltage divider, and a separate alternating-current connection to said voltage divider and between said cathode and one of said electrodesl for regulating the potential of said one electrode in accordance with variations in said voltage to maintain the intensity of said current constant.

WILLIAM E. KIRKPATRICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,169,831 Cawein Aug. 15, 1939 2,173,221 Y Ballard Sept, 19, 1939 2,276,455 Beers Mar. 17, 1942 2,449,524 Witherby et al Sept. 14, 1948

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