US2869029A - Cathode ray beam deflection apparatus - Google Patents

Description

L. DIETCH CATHODE RAY BEAM DEFLECTION APPARATUS Filed April 1, 1954 1N V EN TOR. Z www @M7-CH Jan. 13, 1959 ,Sg@ Patented Jari. 13, SS

CATHODE RAY BEAM DEFLECTION APPARATUS Leonard Dietch, Pennsaiiken, N. J., assigner to Radio Corporation of America, a corporation of Delaware Application April 1, 1954, Serial No. 420,380

4 Claims. (Cl. 315-27) The present invention relates to new and improved electromagnetic deflection apparatus for use in conjunction with a cathode ray tube device and, more particularly, to apparatus designed to suppress undesirable ringing in the deilection circuits.

In deecting a cathode ray beam by means of electromagnetic deection coils, it is difficult to maintain precise linearity of deection in view of the inductance of the coils and in view of certain circuit parameters associated with the coils. Since the deecting coils have a certain amount of inductance, a certain amount of stored energy is present in the deflecting coils at the end of each deflection cycle. lt is possible, through the use of a damping tube or diode, to use a portion of such stored energy for producing a part of the voltage variations and deflecting the cathode ray beam during the initial portion of the next succeeding scanning cycle. Such action is wellknown and is termed reaction scanning. That is to say, the detlecting coils also have certain inherent desirable capacities which, together with their inductance, produce tuned circuits having predetermined recurrent frequencies. During the go time, which is the time of the useful trace of the scanning raster, energy is stored in the magnetic eld of the transformer and deflection coils. The energy contained in the coils will normally be dissipated in relatively high frequency oscillations set up in the coils. In actual operation of present reaction scanning circuits, this stored energy is permitted to produce only one-half cycle of such free oscillation and at the end of the half cycle a damper diode is employed to control or absorb the remaining energy, whereby to suppress substantially completely the remaining cycles of oscillation.

In addition to the free oscillation of the resonant circuit comprising the inductance and capacity of the deflection coils, there also occurs undesirable oscillation of even higher frequency known as ringing Such ringing or parasitic oscillation has been found to result from the leakage reactance of the deflection coils and the transformer from which they derive their energy and is undesirable by reason of the fact that it causes something akin to velocity modulation of the scanning spot intensity. That is to say, ringing normally manifests itself in alternate dark and bright vertical stripes which are present at one side of the scanned raster on the screen of the cathode ray tube. Moreover, ringing has been found to occur despite the use of the conventional damper tube, so that various schemes have been devised for minimizing the parasitic oscillations, most of the known schemes being in the nature of rather complex modifications of the usual circuitry.

It is, therefore, a primary object of the present invention to provide new and improved circuitry for electromagnetic deliection of a cathode ray beam, which circuitry includes means for suppressing or, at least, substantially reducing ringing.

Another object of the invention is that of providing 1 means for effectively cancelling the parasitic oscillations produced in electromagnetic scanning circuits.

In general, the present invention contemplates the provision of an auxiliary tuned circuit for connection in the deflection circuit in such manner as to produce oscillations of the same frequency as the parasitic oscillations which are to be suppressed. Suitable coupling means apply the oscillations of the auxiliary tuned circuit to the deilection coils in such manner as to cancel or buck out the undesired oscillations. In this manner, the ringing is substantially eliminated and, by suitable selection of circuit parameters for the auxiliary tuned circuit, the auxiliary oscillations do not deleteriously aiect scanning linearity.

Additional objects and advantages of the present invention will become apparent to persons skilled in the art from a study of the following detailed description of the accompanying drawing which discloses, by way of block and schematic diagram, an illustrative television receiver embodying a deliection circuit in accordance with the invention.

Referring to the drawing, block 10 represents that portion of a typical television receiver which includes a radio frequency amplier, converter, intermediate frequency amplier stages and the second detector. Details of these circuits are well known to tho-se skilled in the art and need not be described further. Examples of suitable circuits, however, may be found in an article entitled,

Television Receivers, by A. Wright in the March, 1947 issue of the RCA Review.

The input terminals of receiver l0 are provided with composite television signals which are intercepted by an antenna l2. These signals are amplied by the receiver and demodulated in the usual manner so that they appear at output terminal lid, which terminal is indicated for connection to the beam intensity contro-lling electrode of the cathode ray image-reproducing device 16. The video signals demodulated within the receiver lil are or may be substantially clipped to provide horizontal and vertical synchronizing pulses for application to the sync separator circuit 1S via lead 20. The horizontal sync pulses then appearing at output terminal 22 of the sync separator are applied for synchronization of the horizontal deflection signal generator or oscillator 24, while the vertical synchronizing pulses are applied via lead 26 to the vertical deflection signal generator. The output of the vertical deection generator 23 is conventionally connected for driving the vertical deflection output amplifier 30 which, in turn, drives a suitable sawtooth current of iield frequency through terminals Y--Y and the vertical deiiection winding 3l.

rl`he output of the horizontal deflection generator 24 is coupled to the control electrode 32 of a horizontal deflection output discharge tube 34. Suitable biasing potential for the discharge tube screen electrode 36 is conventionally supplied from a source of positive potential indicated at terminal 33 as +B through a screen dropping resistor 4d which is, in turn, bypassed to the cathode 42 via a capacitor 44. A self-biasing cathode resistor i6 whose value is chosen in accordance with the desired operating bias for ampliiier 34 is connected in the cathode circuit of the tube and is bypassed by capacitor dit.

The anode Sti of amplifier 34 is connected to a terminal 52 of an auto-transformer 54 which includes an auxiliary step-up winding 56 connected to the anode 5S of a highvoltage rectifying diode oil. The cathode 62 of rectifier 69 is connected to ground through a filter capacitor 64, so that high voltage for the linal anode (not shown) of kinescope lo may be applied via resistor d6 to the highvoltage terminal 68. The lower terminus 70 of autotransformer 54 is connected through a B-boost capacitor '72 and a linearity control inductance 74 to a source of +B potential at terminal '76.

Another capacitor, such as that indicated at 78,'across which is developed a portion of the B-boost voltage, and which aids in the linearity control action of the inductance 74, is directly connected from the auto-transformer terminal 70 to the +B terminal 76. The horizontal deection winding 80 of the cathode ray deection system is connected in shunt with that portion of the auto-transformer between terminals 70 and 70. The damping device, which comprises, by way of illustration diode 82, is connected in damping relation with the yoke winding 80 through the B-boost capacitor 72 and the linearity inductance 74 taken in combination with the capacitor 78. Accordingly, the anode 84 of damper diode 82 is connected with the +B terminal 70 through circuitry indicated generally by reference numeral 86, while the diode cathode S3 is connected to a suitable point 90 on the auto-transformer.

As thus far described, the apparatus of the drawing is in accordance with conventional practice, except for the inclusion of the circuit 86 which is connected between the anode 84 of diode 82 and the junction of capacitor 72 and inductance 74. Since the operation of reaction-scanning apparatus is well-known, it need not be described in detail here. A full analysis of such operation is given, Ifor example, in an article entitled Magnetic Deflection Circuits, RCA Review, September, 1947, by O. H. Schade. Briefly, however, it is to be noted that the bias on the horizontal output tu-be 34 is so adjusted that, during operation, the driving sawtooth wave form 24 which is provided by the horizontal deflection generator, will produce anode-cathode conduction during a period corresponding to only a little more than half the deflection cycle. Hence, it may be assumed that the horizontal output tube 34- is rendered conductive by the sawtooth wave form 24 during only that time between instants t1 and t2, during which interval anode-cathode current will pass from the positive power supply terminal 76 through the inductance 74 and through the diode 82 to the transformer 54. Such current flow induces some deection voltage and current in the transformer which causes a substantially linear rise in deflection current through the yoke winding 80. At time t2, correspo-nding to the commencement of the retrace interval of the deflection cycle, the discharge tube 34 becomes non-conductive and the magnetic field in the auto-transformer andyoke then collapse, causing oscillation of the primary resonant circuit (i. e. the yoke and its distributed capacitance) at its self-resonant frequency which is normally at least four to five times that of the deflection frequency.

After one half cycle of yfree oscillation, the voltage appearing across the horizontal winding 80 is of such polarity as to cause the diode 82 to conduct, thereby damping the energy magnetically stored in the yoke. The direction of the damping current through the diode 32 is in such direction as to charge the capacitors 72 and 'i8 such that their termini nearer the anode 50 of tube 34 are positive with respect to terminal 76. This current through the diode 82, in accordance with well-known reaction scanning principles, provides the first portion of the current sawtooth through the winding 80, which portion corresponds to the interval between instants t3 and t4 of the sawtooth 24'. By the time t4 is reached, the horizontal discharge tube 34 will have been rendered conductive and this time, by reason -of the bias across capacitors 72 and '78, the diode 32 does not immediately conduct, which therefore causes most of the horizontal output tube anode current to iiow through the autotransformer section between terminals 90 and 70.

As hasV been stated, the description given thus far is in the interest of completeness, since it does not constitute a part of the present invention. In addition to the free oscillation of the so-called primary circuit which occurs during and for a period shortly after re` trace, there also occur undesired parasitic oscillations of substantially higher frequency than that of therrequired retrace oscillation. Such undesired, parasitic oscillations may, for example, be in the frequency range of 100 to 400 kilocycles and are not sufficiently damped by the diode 82.

Moreover, the parasitic oscillations produce the abovedescribed vertical stripes onV the raster scanned on the screen of the cathode ray tube. Thus, in accordance with the present invention, the auxiliary tuned circuit 86 is provided between the anode 84 ofthe damper diode 82 and the junction of the B-boost capacitor 72 and the linearity inductance 74. The tuned circuit 86, which is in series with the damper tube circuit, comprises specically a variable inductance 94 in parallel with a capacitor 96 and a resistor 98. The upper terminal 100 of the tuned circuit 86 is connected to the upper end of the winding Si) through a capacitor 102. Suitable values for the elements of the tuned circuit used in practice are 100 to 400 micro-henries for inductance 94, 1000 micromicro-farads for capacitor 96 and 1000 ohms for resistor 98, the function of which will be described more fully hereinafter. Such values are, however, provided merely in the interest of illustration and are not to be construed as by way of limitation. Capacitor 102 should be of such value as to have lo-w impedance for the frequency of the tuned circuit 86.

In the operation of the circuit with the tuned circuit 86 connected as shown, the surge of current through damper diode 82 commencing at time t3 shock excites the tuned circuit 86 into oscillation at its frequency as determined by the value of components 94 and 96. This frequency is chosen by suitable variation of the inductance 94 until it is substantially equal to the frequency of the undesired ringing in the yoke winding 80. The capacitor 102 coupled between the winding 80 and circuit 86 introduces a certain amount of phase shift and applies the oscillations from circuit 86 to the yoke winding with such phase or polarity as to cancel or buck out the parasitic oscillations in the yoke winding. The resistor 98 is included in the tuned circuit 86 in parallel with capacitor 96 and inductance 94 for the following reason: as will be understood, the parasitic ringing oscillations in winding 80 normally are damped out by the resistance of the winding after a portion of the scanning cycle between times t3 and t4 has been completed. If resonant circuit 86 had a high Q and were to continue to oscillate after the cessation of oscillations in the winding 80, the ringing effects on the scanned raster would be continued, albeit with opposite phase, throughout the scanning cycle which, as will be appreciated, would aggravate the condition existing with prior art circuits. Thus, resistance 98 lowersthe Q of the circuit 36 to match it to the Q of the winding 80 at the parasitic oscillation frequency, so that the oscillations produced by the auxiliary circuit 86 are damped out at the same time as the parasitic oscillation in winding 80 would normally have been damped out. In that manner, the auxiliary oscillations produced by the tuned circuit 86 of the present invention are coupled to the deflection winding 80 in the proper phase and of the proper amplitude to cancel out the inherent ringing of the deection winding and, by reason of the resistance 93, the auxiliary oscillations do not persist beyond the time that the parasitic oscillations did.

While the invention has been described in accordance with a specification embodiment wherein, for example, the deflection winding is connected across a portion of an autotransformer, it should be borne in mind that its principles are applicable to other circuit arrangements. Thus, by way of' illustration, the auxiliary resonant circuit may be advantageously used with substantially any electromagnetic deflection apparatus of the reaction scan-v ning variety, regardless of the specific type of transformer coupling employed. Also, although the coupling between the auiiliary circuit 86 and the coils has been ,ShDWn as acapacitive connection directly between the top of the coils and the resonant circuit, the advantages of the invention may be realized by capacitively coupling the auxiliary oscillations in bucking relationship to any point in the circuit of the deection winding where the parasistic oscillations are present.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In reaction scanning apparatus which includes a deflection winding circuit, an electron discharge device for producing a deection voltage waveform of predetermined frequency, transformer means coupled operatively between such discharge device and winding circuit for causing a deflection current to flow in such winding and a damper tube device in shunt with such winding circuit, such winding circuit having a natural resonant frequency higher than such deflection frequency and being inherently subject to parasitic oscillations of a substantially higher frequency than such resonant frequency, and means for substantially suppressing such parasitic oscillation, comprising a tuned circuit having a resonant frequency substantially equal to said parasitic oscillation frequency and operatively connected in series with such damper tube device in such manner as to be rendered oscillatory by conduction of such damper tube device, and means coupling said tuned circuit to said winding circuit for applying the oscillations of said tuned circuit to such winding in such phase as to cancel such parasitic oscillations.

2. In reaction scanning apparatus which includes a delection winding circuit, an electron discharge device for producing a deflection voltage waveform of predetermined frequency, transformer means coupled operatively between such discharge device and winding circuit for causing a deflection current to ow in such winding and a damper tube device in shunt with such winding circuit, such winding circuit having a natural resonant frequency higher than such deflection frequency and being inherently subject to parasitic oscillations of a substantially higher frequency than such resonant frequency, and means for substantially suppressing such parasitic oscillation comprising a tuned circuit having a resonant frequency substantially equal to said parasitic oscillation frequency and operatively connected in series with such damper tube device in such manner as to be rendered oscillatory by conduction of such damper tube device, and capacitive means coupling said tuned circuit to said winding circuit for applying the oscillations of said tuned circuit to such winding in such phase as to cancel such parasitic oscillations.

3. In reaction scanning apparatus which includes a deflection winding, an electron discharge device for producing a deflection voltage waveform of predetermined frequency, transformer means coupled operatively between such discharge device and winding for causing a deflection current to flow in such winding and a damper tube device in shunt with such winding, such winding having a natural resonant frequency higher than such deflection frequency and being inherently subject to ringing of a certain phase and of a substantially higher frequency than such resonant frequency, and means for substantially suppressing such ringing comprising a tuned circuit having a resonant frequency substantially equal to said parasitic oscillation frequency and operatively connected in series with such damper tube device in such manner as to be rendered oscillatory by conduction of such damper tube device, and a capacitor having low impedance for such ringing frequency coupling said tuned circuit to said winding for applying the oscillations of said tuned circuit to such winding in phase opposition to such ringing phase, whereby to cancel such parasitic oscillations.

4. In reaction scanning apparatus which includes a deflection winding circuit, an electron discharge device for producing a deflection voltage waveform of predetermined frequency, transformer means coupled operatively between such discharge device and winding circuit for causing a deection current to ow in such winding and a damper tube device in shunt with such winding circuit, such winding circuit having a natural resonant frequency higher than such deflection frequency and being inherently subject to gradually damped parasitic oscillations of a substantially higher frequency than such natural resonant frequency, and means for substantially suppressing such parasitic oscillation comprising a tuned circuit having a resonant frequency substantially equal to said parasitic oscillation frequency and operatively connected in series with such damper tube device in such manner as to be rendered oscillatory by conduction of such damper tube device, means coupling said tuned circuit to said winding for applying the oscillations of said tuned circuit to such winding circuit in such phase as to cancel such parasitic oscillations, and resistive means connected to said tuned circuit for damping its oscillations at substantially the rate at which such parasitic oscillations are damped.

References Cited in the file of this patent UNITED STATES PATENTS 2,543,305 Schwarz Feb. 27, 1951 2,553,360 Court May 15, 1951 2,606,306 Bridges Aug. 5, 1952 2,627,051 Barco Jan. 27, 1953

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