US2440418A - Cathode-ray beam deflecting circuit - Google Patents

Description

April 27, 1948. s. l. TouRsHou CATHQDE RAY BEAM DEFLECTING CIRCUT Filed March 9. 1946 2 Sheets-Sheet l QSMMW o INV ENTOR zmnIll/lwz ATTO RN EY AP 27, 1948, s. l. rouRsHou CATHODE RAY BEAM DEFLECTING CIRCUIT Filed March 9, 1946 2 Sheets-Sheet 2 i L w INVENTOR zmwfzz BY im' ATTORN EY Patented Apr. 27,1948

CATHODE-RAY BEAM DEFLECTING CIRCUIT Simeon I. Tourshou, Philadelphia, Pa., assignor to Radio Corporation of America, a corporation of Delaware Application March 9, 19.46, Serial No. 653,261

13 claims. l

The present invention relates to television systems in which the electron scanning beam of a cathode ray tube is electromagnetically deflected cyclically to eect the reproduction of an image, and more particularly relates to means for overcoming such distortion of the image as results from non-linear deiiection of the scanning beam.

Television systems of the above type frequently include a horizontal, or line, deflection circuit in which one or more power output tubes are connected to supply cyclically varying current through a coupling transformer to suitable beam deflection coils which are associated with the cathode ray image producing tube. It is known in such deflection circuits to employ a so-called damper tube, usually a diode or in some instances also a triode, shunted across the beam deflection coils. In such an arrangement, the energy stored in the circuit inductance during the retrace periods of the cathode ray scanning beam causes a current iiow through the damper tube during scansion. This current theoretically may be combined with the current output of the power tube or tubes toa summation characteristic which is linear with respect to time. The theoretically linear summation current thus produced is that which actually flows through the beam deflection coils thereby to bring about a substantially uniform angular deflection of the cathode ray beam at line-scanning frequency.

It has been found in practice, however, that a damper tube of the nature set forth above does not always completely remove the high-frequency oscillations which occur immediately following retrace, and that these high-frequency oscillations, if present, cause a number of vertical bands, or bars, to appear near one side of the image raster, with resulting distortion of the image in this region. These high-frequency oscillations and the eiects thereof may be materially reduced by the use of additional damping means, such as a series 'resistance-condenser combination, acting in parallel with the damper tube circuit.

The utilization of additional damping means to reduce the high-frequency oscillations which occur following retrace, however, has the eiect of lowering the voltage across the beam deection coils near the end of scansion. This is undesira'ble, since the corresponding reduction in current iow through the deiiection coils decreases the beam scanning rate and causes a crowding of the reproduced image near one side of the raster. It has been found that this non-linearity of scan due to a dropping oil. of deection coil current ling the flow of current through the damper tube,

and that as a result of such control, the voltage across the beam deection coils during scansion 1 may be maintained relatively constant. As a consequence, substantial linearity of scan is obtained.

One object of the present invention, therefore, is to provide, in a television system in which a cathode ray scanning beam is electromagnetically deflected, means for causing such deection to occur at a. substantially linear rate with respect to time.

Another object of the invention is to provide, in a, television system of the nature set forth, means forl reducing the amplitude of the highfrequency oscillations which occur following retrace, and additionally to prevent the use of such means from aecting the linearity of scan near the end of the trace portion of each deflection cycle.

A further object of the invention is to provide, in connection 'with a television circuit of the nature set forth, which includes a damper tube, means whereby the ow of current through such damper tube may be controlled through the application thereto of a voltage which varies as a function of the current output of the power tube, and also to provide means for controllably delaying the phase of this voltage.

Other objects and advantages will be apparent from the following description of a preferred form of the invention and from the drawings, in which:

Fig. 1 is a circuit diagram of a preferred embodiment of the present invention;

Figs. 2 and 3 are sets of waveform-s useful in explainingfthe operation of the circuit of Fig. 1; and

Figs. 4 and 5 are modifications of the circuit of Fig. 1.

Referring rst to Fig. 1, there is shown a television' deflection and high-voltage rectifier circuit which includes a horizontal power output tube I 0. Power tube IIJ is adapted to supply, when voltage variations which may have a waveform such as indicated by the reference character I2 are applied to the control electrode thereof, cyclically varying current to a. pair of horizontal, or line. cathode ray beam deection coils I 4 through a coupling transformer I6.

Transformer I6 is provided with a primary winding I8, a step-up winding 20 forming in eiiect an extension of the primary winding I8,

and a secondary winding 22. This secondary cathode ray beam deflection coils I4, which, together with a pair of vertical, or ileld, deflection coils 24 preferably form part of a. yoke assembly encircling the neck of a cathode ray imagereproducing tube or kinescope 26. The vertical cathode ray beam deflection coils 24 are energized by sawtooth current of field-scanning fre# quency from a deflection generator 28, which may be of any suitable design. It will not, therefore. be described in detail.

During operation of the` circuit of Fig. 1, as will be later brought out, voltage surges are produced across the primary winding I8 of transformer I6. These voltage surges are steppedup by the winding 20 and applied to a surge-type rectifier 36, which may, for example, be of the type disclosed in a copending U. S. patent application of Otto H. Schade, Serial No. 578,678, illed February 19, 1945, or in a copending U. S. patent application of Albert W. Friend, Serial No. 631, 732, filed November 29, 1945. The output of rectier 30, which is a substantialy smooth D. C. potential, is applied to the second anode 32 of the kinescope (cathode ray image ,producing tube) 26 over conductor 34. i

'Ihe voltage variations I2 applied to the control electrode of power tube ill, together with its bias potential, produce a rising current in tube i0 during scansion, such as represented by the waveform portion 36 in Fig. 2. This current is cut of! at the beginning of retrace time.

The current in the deilection coils I4 and transformer I6 does not disappear at the instant of cut-off of tube I0, however, due to the inherent distributed capacity of the circuit. This distributed capacity, at the instant of the beginning of retrace, is charged to a relatively low voltage.

'I'he inductance of the deflection coils I4 and transformer I 6, together with the above-mentioned distributed capacity, forms a tuned circuit in which high-frequency oscillations would normally be produced. These oscillations begin with the start of retrace time, and one-half cycle of the natural period of oscillation of the circuit is represented by the curve portion 38 in Fig. 2. After one-quarter cycle, the current in the deflection coils I4 is reversed, and the oscillation is stopped after one-half cycle near the negative current peak. The means for producing such a result include the series combination of a damper tube 40 and a condenser 42 connected across the secondary winding 22 of transformer I6.

During retrace, that is, during the half-cycle of the natural period of oscillation of the circuit, the current in both tubes I0 and 40 is completely blocked, the voltage as represented by the waveform portion 44 (Fig. 2) reaching a high value at one-quarter cycle when the current passes through zero. In order that linear deflection of the cathode ray beam be produced, itis necessary that the rate of change of the current in the deflection coils I4 be maintained constant during the scanning portion Vof the deflection cycle, as shown by the solid-line waveform portion 46 in Figure 2, and, as long as this rate of change of current is constant, the voltage across the deilection coils I4 will remain steady at a predetermined level, as represented by the solidline waveform portion 48.

The polarity of the voltage applied to the anode of the damper tube 40 immediately following retrace is such as to cause the damper tube 40 to conduct. The waveform of the normal current ilow through tube 40 may be such as indicated 4 in Fig. 2 by the solid-line waveform portion 66.

When the damper tube current represented by the curve 66 in Fig. 2 is properly matched with the power tube current represented by the curve 36. the summation of these currents will have a linear characteristic as shown by the solid-line curve portion 46, and hence this curve 46 represents the current actually owing through the deflection coils I4 during scansion.

It has been found in practice, however, that it is dimcult to remove completely the high-frequency oscillations which occur following the retrace portion of each deection cycle through the use of the damper tube circuit 46, 42 alone, and, as a result, a number of alternate light and dark vertical bands appear near one side of the image raster. To assist the tube 40 in damping out the high-frequency oscillations that cause these vertical bands and consequent image distortion, the condenser 42 is chosen to be of relatively low value, and a resistor 52 is employed in parallel with the damper tube 40. The R.C. combination 52, 42 is thus also shunted across the secondary transformer winding 22, and, together with the damper tube circuit 40, 42, results in substantially complete elimination of the highfrequency oscillations which normally are produced in the manner set forth above.

When condenser 42 is chosen to be of relative low value, however, the voltage appearing across the deflection coils I4 during scansion does not remain constant. Instead, this voltage falls oil, as shown by the broken curve portion 54, near the end of the scanning interval. The current through the deflection coils I4 likewise departs from linearity in the manner indicated by the broken curve portion 56.

vTo overcome the above undesirable effects, the upper plate (in the drawing) of condenser 42 is connected to the upper plate of a further condenser 58 through a variable inductance 60. The lower plates of the two condensers 42 and 56 are Joined together. The primary winding I8 of transformer I6 is connected to` condenser 58 in such a manner that when the plate current of power tube I0 varies duringscansion, as shown by the curve portion 36 in Fig.'2,ra."varying voltage will be developed across condenser 58. The waveform of this varying voltage may be such as indicated by the reference character 62 in Fig, 3. 'Ihe positive peak 63 o1' this voltage waveform 62 occurs substantially at the mid-point in the scanning portion of the deilection cycle.

The voltage thus developed across condenser 58 is applied to condenser 42 through the variable inductance 66. The effect of inductance 60 on the voltage waveform 62 is to delay the occurrence of the positive peak 63 of the wave.

The voltage across condenser 42 may, therefore,

have a waveform somewhat similar to that represented by the reference character 64, the phase of the positive peak 63 being shifted so as to occur later in the scanning interval.

' The current through damper tube 40 normally decreases toward the end of scansion in the manner indicated by the solid waveform portion 50 in Fig. 2. However, as stated above, a voltage which may be such as represented by waveform 64 is applied across condenser 42. Since the upper plate of condenser 42 is directly connected to the cathode of tube 40, the voltage developed across condenser 42 varies the conduction characteristics of tube 46. This variation is such that the current flow through tube 40 decreases at a more rapid rate near the end of the scanning period.

andere as illustrated bythe broken-line curve portion Ormea Since the ldamper tube circuit l0, 42 is in shunt with the denecuon cons u, uns reduction in dampertube current as shown -by the waveform portion 68 acts to eliminate. by reason of the combination of curves 50 and 36. the nonlinear portion 56 from the otherwise linear current curve 46. Such an expedient eliminates the crowding of the reproduced image near one side of the image raster, and, since distortion near the opposite side due to high-frequency oscillations following retrace is materially reduced by the additional damper circuit 52, 42, the reproduced image is left substantially free from these two undesirable features.

The amount by which the instant of occurrence of the positive peak 63 of wave 64 may be delayed is controllable by varying the value oi inductance Bil. This inductance 60 may beofany suitable type such, for example, as a permeability-tuned inductor. Normally, the value of inductance 60 is selected so as to compensate for the non-linearity of scan introduced through the use of the R.- C. combination 52, 42, but it may also be selected so as to compensate for non-linearity which would otherwise result from an improper matching of damper tube current and power tube current as shown in Fig. 2. Furthermore, the present invention is useful in overcoming non-linearity which is inherent in wide-angle kinescopes the faces of which are either ilat or substantially so. This is due to the fact that movement of the electron scanning beam across the surface of such fiatfaced kinescopes is a tangential function of the angular deflection of the beam.

The anode of the power output tube Ill is connected to the B+ terminal in Figa-1 through a D. C. path which includes the primary Winding I 8 of transformer I6, the inductance B0, the resistor '52, and the secondary transformer winding 22. AS a result of this connection, the voltage developed on the capacitor B2 during operation of the system is of such polarity as to increase, or boost the voltage of the power source connected to the said B+ terminal. Accordingly, the energy thus recovered from the secondary circuit may be utilized to obtain greater scanning power in the manner set forth, for example, in a copending United States patent application of Otto H. Schade, Serial No. 593,161, led May 11, 1945, or in a copending United States patent application of Charles E. Torsch, Serial Number 610,368, filed August 11, 1945. Conversely, the power source connected to the said B+ terminal may be reduced in value by an amount substantially equal to the value of the energy recovered, while maintaining the same scanning output.

In practice it has been found that values of .05 mf. for capacitor 42, .035 mf. for capacitor 58, and 5 to 15 microhenries for inductance 6G. are suitable for obtaining the results described. However, these values may be altered to suit various operating conditions and in accordance with the values of the other components of the circuit.

Figs. 4 and 5 show modications of the circuit of Fig. 1. In Fig. 4 the inductor 60 is of fixed value, and a pair of additional variable inductors 66 and 68 are employed, the inductor 66 being eiectively in series with the capacitor 42, as

6 that a portion of the latter is eifectively in sexies with capacitor 42. A second tap 10 on inductor Il has connected to it the lead from primary winding i8 of transformer i6, so that another portion oi' the inductor 60 is eifectively in series with capacitor IB.

It will be appreciated that the waveforms of the currents and voltages shown in Figs.' 2 and 3 are given merely as an aid in understanding the operation of the circuit of Fig. l, and do not necessarily represent the actual amplitudes or durations ot these currents and voltages.

Having thus described my invention, I claim:

1. In a television system in which a power output tube is adapted to deliver cyclically varying current through a coupling transformer to the electromagnetic beam deilection means associated with a cathode ray tube wherein an electron beam is developed and then deiiected by the passage of said current through said deflection means so as, to scan a target area, and in which means, including a diode, are provided in shunt with said coupling transformer for damping out oscillations which would normally be produced during a portion of each current cycle in part by the inductance of said coupling transformer and said deection means, the combination of means for deriving a cyclically varying voltage from the cyclically varying current delivered by said power output tube, means for delaying the phase of the said cyclically varying voltage, and means for applying said phase-delayed voltage to the cathode of said diode.

2. A television system in accordance with claim 1, in which said phase-delaying means is adjustable to vary the delay interval. l

3. A television system in accordance with claim 1, in which said phase-delaying means comprises shown, and the inductor 68 being eiectively in A series with the capacitor 58. Fig. 5 utilizes the adjustable inductor 60 of Fig.. 1, but illustrates the manner in which the cathode of damper tube 40 may be connected to a tap on this inductor so a permeability-tuned inductor.

4. In a television system employing a cathode ray tube wherein an electron beam is developed and then deiiected to scan a luminescent surface, and in which the means for deecting said electron beam includes means for generating a cyclically varying current, at least one deflection coil associated with said cathode ray tube, means i'or coupling said generating means to said deilection coil, and means including a two-element electron discharge device for damping out undesired voltage oscillations produced across said deflection coil, the combination of means for developing a voltage which varies as a function oi' variations in the current output of said generating means, means for altering the Waveform of the said 'developed voltage, and means for applying the voltage the waveform of which has been so altered to one element of the said two-'element electron discharge device. f

5. A television system in accordance with claim 4, in which said waveform-altering means comprises means for delaying the phase of said developed voltage.

6. A television system in accordance with claim 4, in which said two-element electron discharge device isa diode, the output of said waveformaltering means being applied to the cathode of said diode.

'7. In a television system in which a power output tube is adapted to deliver cyclically varying current through a coupling transformer to a pair of deflection coils associated with a cathode ray tube wherein an electron beam is developed and then deiiected by passage of said current through said deflection coils so as to scan a luminescent target, the combination of a damper tube, having at least an anode and a cathode, and a first condenser connected in series across said pair o: deiiection coils so as to reduce the amplitude of oscillations which would normally be produced during a portion of each deiiection cycle in part by the inductance of said coupling transformer and said deflection coils, a further condenser, means for connecting said further condenser to the primary winding of said coupling transformer so as to develop across said further condenser a voltage which varies as a function oi variations in the current flow through said primary winding, an inductor, and means for applying the voltage developed across said further condenser through said inductor to the cathode of said damper tube.

8. A television system according to claim 7, further comprising means for varyingthe value of said inductor.

9. A television system according to claim '7, fui'- ther comprising an impedance element connected in parallel relation with said damper tube so as to further reduce the amplitude of said oscillations.

1D. In a television system in which a cyclically varying current is generated and delivered to at least one cathode ray beam deflection coil through an inductive coupling member, the combination of a diode and a condenser connected in series across said cathode ray beam deflection coil, the cathode of said diode being connected to one plate of said condenser, an inductor, said one plate of said condenser also being connected to one terminal of said inductor, a further condenser having one plate connected to the other terminal of said inductor, means for connecting the remaining plate of said further condenser to the remaining plate of said first-mentioned condenser, and means for connecting said one plate of said further condenser to a point on said inductive coupling member.

11. In a televisionsystem in which a cyclicaily varying current is generated and delivered to at least one cathode ray beam deiiection coil through an inductive coupling member, the combination of a diode, a iirst inductor.v and a nrst condenser connected in series across said cathode ray beam y a second inductor having one terminal thereof connected to the cathode of said diode. a third inductor. and a second condenser connected in series, the terminal of said third inductor opposite to that which is connected to said second condenser being joined to the remaining terminal of said second inductor. means for joining together the unconnected plates of said first and second condensers, andvmeans i'or connecting said inductive coupling member to the said remaining terminal o! said second inductor.

12. A television system in accordance with claim 11, in which said rst and third inductors are each adjustable.

13. In a television system in which a cyclically varying current' is generated and delivered to at least one cathode ray beam deflection coil through an inductive coupling member, the combination of a diode having an anode and a cathode, the anode of said diode being connected to one end of said cathode ray beam deflection coil, a iirst condenser, a second condenser, one plate of each of said condensers being connected to the remaining end of said cathode ray beam deiiection coil. an inductor, means for connecting the ends of said inductor between the remaining plates of said rst and second condensers, means for connecting the cathode of said diode to a tap on said inductor, and means for connecting said inductive coupling member to a further tap on said inductor.

SIMEON I. TOURSHOU.

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