US2110245A - Deflecting circuit - Google Patents

Description

A. C. STOCKER DEFLECTING CIRCUIT Filed April 27, 1935 @www v copa N .LA/suena aub/7d '-mllll. )l

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INVENTOR Arthur CJ'OC/Pier Patented Mar. 8, 1938 n UNITED STATES fPii'TENT OFFICE y DEFLECTING CIRCUIT Arthur C. Stocker, Haddon Heights, N. J .,v assignor to Radio Corporation of America, a corporation of Delaware Application April 27, 1935, Serial No. 18,492

6 Claims. (Cl. Z50-36) My invention relates to deecting circuits for of the voltage applied to the grid of the output cathode ray tubes and particularly to deecting tube would be wrong as will be apparent from circuits for producing a deflecting field o f sawthe description which follows. tooth Wave form. Other objects, features and advantages of my One of the problems encountered in designing invention will appear from the following descripv5 deecting circuits, especially deecting circuits tion taken in connection with the accompanying for usein television receivers, is that of obtaindrawing, in which ing a deecting current or voltage of suiicient Figure 1 is a circuit diagram of a cathode ray amplitude without employing too many amplifier tube delecting circuit embodying my invention, tubes. Fig. 2 is a group of curves which are referred 10 It is, accordingly, an object of my invention t0 to in explaining my invention, provide a cathode ray tube deiiecting circuit Fig. 3 is a curve showing the character of the which includes the minimum number of amplivoltage impressed upon the grid of the output Iier tubes and which supplies a defiecting eld of tube, and n v l5 the desired amplitude. Fig. 4 is a characteristic curve of the output 15 A further object of my invention is to provide tube and a curve of input voltage. an improved deecting circuit for operating an Referring to Fig. 1, the horizontal def'lecting output tube by driving its grid positive. circuit of a television receiver is illustrated. It A further object of my invention is to provide comprises an electric discharge tube yI which may an improved method of and means for producing be of the three-electrode type having a cathode 20 a voltage of saw-tooth wave shape. 2, a control grid 3, and an anode 4. A positive A still further object of my invention is to provoltage is applied to the anode 4 from any suitvide an improved circuit for generating a voltage able direct current source which is exemplified having a saw-tooth component and having an by the voltage divider 6. Between the cathode 2 impulse component which is in the positive dand ground there are connected a resistor R1 and 25 rection. a condenser C1 whereby the condenser C1 may be In the preferred embodiment of my invention I charged through the tube I and the resistor R1. connect a condenser in the cathode lead of an 'Ihe condenser C1 is shunted by a resistor R2 electric discharge tube and charge the condenser which has a high resistance as compared to the 3o in a short period of time and discharge it during a resistance of resistor R1, whereby a charge on 30 comparatively long period of time whereby a sawthe condenser will leak ou gradually theretooth voltage vappears thereacross. This voltthrough. In the input circuit of the tube l, a age is supplied to an output tube through an grid resistor'l is connected between the grid 3 ampliiier stage whereby the input circuit imand thelower end of the resistor R1. If prepedance of the output tube may be made low ferred, the lower end of grid resistor 1 may be 35 enough to permit driving the grid of said output connected directly to the cathode 2. tube positive, thereby obtaining maximum output. It Will be apparent that, if positive voltage im- The input circuit of the output tube must have pulses are applied periodically through a vconlow impedance if the tube is operated in this `denser 5 to the grid 3, the plate impedance of the 40 way because during the period its control grid is tube will be lowered sufiiciently for the duration 40 positive the input impedance of the tube drops to of a positive impulse to permit the condenser C1 a comparatively low value. Therefore, in order to be charged from the direct current source 6 to maintain the input circuit impedance ofthe to produce the steep portion of a saw-tooth voltoutput tube substantially constant, it is necessary age across the said condenser. At the end of a to connect a low impedance grid resistor across positive voltage impulse, the plate impedance of 45 the input electrodes of the tube. the tube I becomes very high and the condenser It is because of the necessity for a low im- C1 gradually discharges through the resistor Rz pedance input circuit that a tube so operated to produce the vgradually sloping portion of the cannot be connected directly across a saw-tooth saw-tooth voltage. The plate impedance of the generating circuit of the type commonly emtubel is high during the period between positive 50 played, a circuit of this type being shown in Fig. impulses because of the negative bias supplied "22 of French Patent No. 738,475 having a dlivr by the grid leak detector action of the condenser date of October 17, 1932. If a single amplifier 5 and resistor 1. l stage were inserted between such a saw-tooth The positive voltage impulses may be supplied generating circuit and the output tube, the phase from any suitable source such as a relaxation y55 oscillator 8. The particular oscillator illustrated is a blocking oscillator which includes an electric discharge tube 9 having a cathode Il, a grid I2 and a plate I3. The plate circuit of the tube 9 is coupled to the grid circuit of the tube through the windings I4 and I6 of a transformer I1. The transformer winding I6 is connected in series with a gridcondenser I8 which becomes charged periodically to block the tubef`9.- Angrid, resistor I9 is connected between the grid I2 and the cathode II whereby, after the tube has been blocked, the condenser I8 discharges through the resistor I9 to permit the beginning of the next blockingV cycle. In the specic embodiment beingv described, the oscillator was adjusted to supply,

'7290 impulses per second.

The voltage impulses produced by the oscillator 8 are impressed upon the grid 3 of the electric discharge tube through a third winding 2 I of the transformer I1`and through the coupling condenser 5. fv Y e `As a result ofthe periodic positive voltage impulses being impressed upon the grid 3,- the condenser C1 is charged rfor a period corresponding tothe durationpof the positive impulse'and is "discharged for a period correspondingltothe interval between positive impulses,whereby a voltage appears across the condenser C1 which has the Wave yform indicated by the curve` 22 in Fig. 2. The voltage appearing across the resistor R1 hasthe wave form indicated by the curve 23 in Fig. 2, while thev combined voltages Vappearing across R1 vand C1 have the wave shape indicated by the curve 24. It Will be noted that-theim pulse-component of the voltage-wave, that is, the voltage appearing across resistor R1, is in the positive direction. l l i Since the impulse vcomponent is in the positive direction, theV combined voltage appearing across resistor R1 .and condenser C1 may be supplied to an output tube 26 through a single amplier stage including an amplifier tube 21, and'the voltage limpressed upon the grid vof the`ou'tput tube will have the polarity indicated by: the. curve 28 in .-Fig. 3. 'Ihis is the polaritywhichis-irequired .for-.best operation where d'eflectingfcoilsare` employed, because thekv grid of the output tube should be driven'negative at'the 'endfof the gradually `sloping portion of thesaW-tooth in order that rtheoutput tube shall bel driven close to cut-off whereby avr high voltagewilljappear across the deflecting coils to give a fast' return line.v Y The amplier tube 21 may be of lany suitable type, the-one iny thefcircuitillustrated'being a vacuum tube Iof the pentode type which has lits input circuit'coupled" across the resistor'Ri and the condenser Ci'by/ means of a coupling condenser 29 and a connection through ground. The outputlcirrcuit of the tube 21 is coupled vto the input'circuit'of the output 'tube V26' through a coupling condenser 3I.`

Since itis desired to drivethefgrid of the output tube positive in order to obtain maximum output, a resistor 32 of comparatively low resistance `is connected between' the grid `l33 and the' cathode 34.' In one embodiment of the inventior'rthis`v resistor was givenV a vajlue'of'faplproximatelyV 2500 ohms, `this value/being considerably vlower than the input impedance ofthe tube during the timethat its grid is driven positive( During the period the grid ofthe 'tulbe isfpositive, its. input impedance maybe ofthe order of 8000 ohms. n In` thisconnection it mair be noted thatV the coupling condenser -3`I`l and-the grid resistor 32 have a grid leak detector biasing action so that the output tube actually has small negative bias on the grid 33.

Referring to Fig. 4, the curve 30 shows the static characteristic of the output tube 26. The voltage applied to the grid 33 is represented by the curve 4E). As will be seen by referring to this figure, the grid 33 of the tube 26 is swung over substantiallythe yentire ,straight lportion of thejcharaeteristic curve.- Since this causes the input impedance of the tube 26 to drop from a v ery high value when the grid is negative to the comparatively low input impedance mentioned w above,` it is necessary that the low impedance resistor 32 be connected across the input electrodes of the tube for the purpose of maintaining the impedanceof the input circuit of the output tube substantially constant. It will be apparent that such a low impedance input circuit cannotbe connected directly across a saw-tooth generating circuit. Thus, at least one ampliiier Vstagefrnust 'be inserted between the saw-tooth vgenerating'circuit and the output tube. By utilizing Amy invention a single 'amplifier stage transfers the defleoting voltage totheinput circuit of vthe-output tube with the proper polarity.`

The@ output circuit'oiI theoutput tube 26 is coupled through a coupling-condenser 36 to the deecting coils 31 of a cathode ray tube 38.

lIn -some cases` it may be preferred to employ a screen grid tube in place of the three-element tube 26 in the output stage of kthe `deflecting circuit. In that case, becausefof the high plate impedance of the `screen' grid tube, the peaking resistor R1 may be omitted. and the saw-tooth component only of the deecting wave impressed upon the grid ofthe output tube. i v Whilethe values of R1, R2, and Ci are not critical, Vthe following values'have Vbeen found to be satisfactoryin 'the embodiment illustrated: R1 of the order of 5000 ohms,'R2=60,000 ohms and C1=.015 microfarad. 'n v From the-foregoing description itwillbe apparent that various modifications may be made in myrin'vention withoutdeparting from the spirit "and scopethereof, and I desire, therefore, that only such limitations shall be placed thereon as Vare necessitated bythe prior Aart and set'forth in the'appended claims. i

.of said rvoltage impulsesj being impressed upon said grid, and means for discharging said con- :denser through said resistor whereby saw-tooth voltage waves are produced periodically across said condenser, the discharging ycircuit including vsaid resistor beingsubstantially `non-inductive.

2. The invention vaccording to Vclaim l characterized in that a peaking resistor is connected .in series with the cathode-anodespace path of said electric discharge Vtube and saidv condenser. 3. In a ,cathode ray tube deflecting circuit, an

electricdischarge tube of the high vacuum type having a cathode, aY control grid and an'anode, a condenser connected between said cathode and ground, a resistory shunted across 'said' condenser,

means for maintaining said anode at a positive potential with respect to vground Whereby'said condenser is charged throughrsaid tube in response to 4I'Jos'itiv' voltage impulses being impressed upon said grid, means for maintaining said grid negative during the periods between said positive impulses, an amplifier tube having an input circuit, and means for impressing the voltage appearing across said condenser upon said input circuit.

4. 'Ihe invention according to claim 3 characterized in that a peaking resistor is connected in series with the cathode-anode space path oiv said electric discharge tube and said condenser and between said cathode and ground, and further characterized in that the resistance of said peaking resistor is low compared with the resistance of said shunting resistor.

5. In a circuit for producing a flow of sawtooth current through an inductance coil, an electric discharge tube having a cathode, a control grid and a plate, a condenser connected between said cathode and ground, a resistor connected across said condenser, means for applying a steady positive voltage to said plate whereby periodic positive impulses impressed upon said grid cause a saw-tooth voltage to appear across said condenser, an output tube having an output circuit for coupling to said coil and having input electrodes, including a control grid, shunted by an input resistor, and an amplifier tube having an input circuit connected across said condenser and having an output circuit coupled across said input resistor, said input resistor having a resistance value which is 10W compared with the input impedance of said output tube when its control grid is driven positive.

6. In a circuit for producing a flow of sawtooth current in an inductance coil, an electric discharge tube having a cathode, a control grid and a plat-e, a peaking resistor and a condenser connected in series between said cathode and ground, a resistor connected in shunt to said condenser, means for applying a steady positive voltage to said plate whereby periodic positive impulses impressed upon said grid cause a sawtooth voltage to appear across said condenser and an impulse voltage to appear across said peaking resistor, an output tube having an output circuit for coupling to said coil and having input electrodes, including a control grid, shunted by an input resistor, and an amplifier tube having an input circuit connected across said peaking resistor and said condenser and having an output circuit coupled across said input resistor, said input resistor having a resistance value which is low compared with the input impedance of said output tube when its control grid is driven positive.

ARTHUR C. STOCKER.

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