US2449969A

US2449969A - Compensating device

Info

Publication number: US2449969A
Application number: US596473A
Authority: US
Inventors: Wright Antony
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1945-05-29
Filing date: 1945-05-29
Publication date: 1948-09-28
Anticipated expiration: 1965-09-28

Description

Sept., 28, w48. A'. WRIGHT COMPENSATING DEVICE Filed May 29, 1945 NEE QN NMDA dnvm.

ATTORNEY Patented Sept..v 28?. 194

2&4199969 @OENSTNG DE Antony Wright, 'Del Rao Corporation o? d Delaware Hill, Pa., assigner to marica, a corporation ci Application May 29, 19de, @i No. 596,473

(Cl. S15-B27) 13 CEP.

The present invention relates 'to cathode ray beam deecting circuits and especially to circuits ci the type adapted for use in television transmitting and receiving systems. In systems of this type a saw-tooth wave of current is caused to flow through the deecting coils associated with a cathode ray tube so as to produce a controlled electromagnetic field which brings about a deiection of the cathode ray beam. It is desirable that this deection shall occur in a substantially linear manner with respect to ity image production on the tube viewing target.

In order to obtain a sawtooth current having a large peak amplitude, such, for example, as required for the horizontal scanningA of an image raster (that portion of the tube target area which is scanned by the cathode ray beam), it is customary to supply cycllcally varying current from a power tube to the horizontal defiecting coils of the cathode ray tube through a vpltage step-down transformer. Furthermore, to improve the linearity of the current owing through the delecting coils. a. so-called ldamping tube is usually connected across the delecting coilsin such a manner that the current ow in the damping tube circuit adds -to the current output of the power tube to result in a substantially linear summation current ilow through the deflecting coils.

The peak amplitude ofthe current owing through 'the horizontal deflectlng coils determines the width of the scanning pattern. It may be controlled -in several ways, such, for example, as

by varying the strength of the D.C. potential applied to the anode of the power tube, or by changing the waveform of the voltage variations applied to the control electrode thereof. Such expedients,V however, cause changes in the peak amplitude of the -plate current of the power tube. This is frequentl'y' undesirable, since the resistance of the damping tube circuit, in many types of scanning systems, has a xed value which is selected to be suitable for a power tube current output of approximately a predetermined magnitude. Consequently, a change in the peak amplitude of the power tube current ilowing through the defiecting coils in such circuits results in a summation current which is appreciably non-linear and which may cause distortion of the reproduced image.

The above condition may also be present in systems designed to have a scanning pattern of fixed size. It has lbeen found in such systems that commercial variations in the constants of tubes, transformers, land other circuit components result in deviations from the normal amplitude of the currents in the deiiecting coils. and that any time to insure high qualtube or the waveform adjustment of the circuits required to produce the exact normal amplitude will cause a considerable departure from the normal lineari-ty of the scan. Thus, the requirement for a. horizontal size adjustment is that it should compensate for commercial variations in circuit constants for size only without any edect on linearity. The high voltage should remain constant under the condition of adjustment for size.

It is, therefore. a principal object of the present invention to provide means whereby the width of .the image raster scanned by a cathode ray beam in a television scanning circuit may be adjusted without varying either the strength of the D.C. potential'applied to the anode of the power of the voltage variations applied to the control electrode thereof.

It is another object of the present invention to provide. in a cathode ray beam television scanning circuit, a variable inductance connected across .the horizontal deflection transformer secondary winding, whereby the image raster scanned bythe cathode ray beam may be adjusted -to substantially a predetermined width.

It is a still further object of the presen-t invention to provide simple and eective means in a cathode raybeam scanning circuit for compensating for changes in the width of the scanning pattern caused by deviations of the circuit components from their rated electrical values.

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

Fig. 1 is a diagram. of a cathode ray beam deecting circuit incorporating one form of the present invention; and

Fig. 2 is an explanatory graph to assist in explaining the operation of the circuit of Fig. 1.

In Fig. 1 is illustrated a television scanning circuit including an output power tube iii, which cmay, for example, be of the type known as the 6L6. The anode of tube it is connected to the positive terminal I2 of a source of voltage (not shown) through a portion of the primary winding i6 of a voltage step-down transformer i8. The negative terminal of the voltage source may be considered as being grounded. A pair of horizontal beam deecting coils 20 which may have a value of 8 to 10 the secondary winding |18 of the transformer i6. The coils 20 may, for example, form part of the deilecting yoke surrounding the neck of a cathode ray tube. The deiecting yoke, per se', is well known. It may be of the type disclosed by Tolson millihenries is connected acrdss 3 patent, No. 2,155,514, or it may be of any other desired form. The cathode ray tube itself may be of conventional design, and is consequently omitted from the drawing for the sake of clarity of illustration.

Centering of the image raster is accomplished by means of a potentiometer 22, one end of which is connected to ground, while 'the other end is connected to the positive terminal 24 of Ia source of voltage (not shown). I'he lower end (in the drawing) ci the secondary winding I8 of transformer I is connected to a suitable tapping point 25 on the potentiometer 22. An adjustable tap 28 on the potentiometer is connected to the lower end of the deflecting coils 20, and permits variations in the amount of direct current from the voltage source connected to the terminal 24 which iiow-s through Ithe deecting coils 20. Adjustment of this tapping point controls the centering of the image raster in a manner known in the art.

The power tube I ode resistor 28, in

0 is biased by means of a cathparallel with which is a bypass condenser 3U. Voltage variations of suitable waveform, such as those indicated by the reference character 32, are applied between ground and the control electrode 34 of tube I0. Across that portion of the former I6 which forms a part of the anode-cathode circuit of tube I8 a damper tube 36 is convnected. Thi-s tube, which is illustrated as a diode, is in series with a parallel resistor-condenser combination 38.

The power tube I8, by reason of the waveform of the volt-age 32 applied to its conrtol electrode 34, permits a current ow from the D.C. source connected to terminal I2 into the primary winding I4 of transformer I6, and this current ow increases during the latter portion of each scanning cycle. One example of such an operating condition of tube I is indicated by the waveform portion 40 in Fig. 2.

When the current in the primary winding I4 is reversed, the damper tube 36 acts to control the dissipation of the energy stored in the winding I4 in its own internal resistance during'the time that tube II) is conductive. The value of the current in the damper tube circuit, which includes damper tube 3B, resistor-condenser combination 38, and a part of -primary winding I4, as well as the rate of change of this current, is determined by the parameters of the circuit, and in paticular the time constant of the resistor-condenser combination 38. The effect of changes in the time constant of resistor-condenser combination 38 on the waveform of current in the damper tube circuit is disclosed in U. S. Patent No. 2,309,672, issued February 2, 1943, to O. H. Schade, and will, therefore, not be described in detail. One possible waveform of current in'ithe circuit of damper tube 3 6, erence character 42. 'Ihe current inthe deflecting coil circuit, that is, 4the circuit which includes the secondary winding I8 and the -coils 20, due to -the power tube IU, as indicated by the waveform 40 in Fig. 2, and the current in the circuit of damper tube 35, as indicated by the waveform 42, combine to produce the linear summation current characteristic denoted by the reference character 44. This linear current waveform 44 represents the current actually flowing through the deecting coils 2D during the scanning interval. For -a further discussion of the principles involved in this operation, reference is made to United AStates Patent No. 2,280,733 to W. A. Toison, United primary winding AI4 of trans-- however, is indicated in Fig. 2 by the ref- 4 States Patent No. 2,382,822 to O. H. Schade, and two copending applications of Otto H. Schade, Serial No. 572,712, filed January 13, 1945, and Serial No. 573,437, filed January 18, 1945.

If desired, the voltage developed across that portion of the primary winding I4 of transformer I6 connected in the anode-cathode circuit of power tube I0 may be stepped up and applied to a high voltage rectifier (not shown) over a conductor 46. The rectiiied energy may then be used as the high voltage supply source for the cathode ray tube, or other apparatus.

The time constant of the resistor-condenser combination 38 is predetermined in accordance with the normal rated values of the other components ofthe system. Likewise, the rate of increase in the current output of power tube I0 during scansion is chosen to combine with the rate of current decay in the damper tube circuit during the same period to produce a linear deflecting coil current in the manner illustrated in Fig. 2.

The present invention includes means for regulating the width of the image raster without varying appreciably the waveform of the power tube current either through a change in the anode voltage of the power tube or through a change in the waveform of the voltage variations applied to the control electrode thereof which would produce non-linearity of scan. This means comprises a variable inductance member 48 connected across the secondary winding I8 of the transformer I6. The inductive member 4B is preferably of the type having an adjustable core section. It may, for example, have a maximum value of several millihenries. Variation of the value of the inductance 48 is thus brought about, preferably, by a variation of the position of the adjustable core element 49 which is formed of. either magnetic or comminuted magnetic material.

By varying the magnitude of the inductance shunted across the transformer secondary winding I8, (and hence across the deecting coils 20), the width of the image raster may be adjusted to compensate for changes therein caused by deviations of the various circuit components from their rated electrical values. This method of width control does not adversely affect to any appreciable extent the linearity of current flow through the deecting coils 20 which may result, as above brought out, from a change in the predetermined waveform of current output of the power tube I0.

Having thus described my invention, I claim:

1. In a cathode ray beam deflecting circuit of the type in which a cyclically varying current having a waveform a portion of each cycle of which is substantially linear with respect to time is caused to flow through a cathode ray beam deilecting coil to thereby result in substantially linear deection of the cathode ray beam during the substantially linearly varying portion of each current cycle, said circuit including an inductive coupling element, a controlled power tube connected to supply cyclically varying current to said cathode ray beam deflecting coil through said inductive coupling element, a rectifier circuit connected across said inductive coupling element, said rectifier circuit including means for shaping the waveform of the current flowing through the rectier circuit, a source of voltage variations, and means for applying voltage variations from 'said source to said power tube so as to produce a current output therefrom which adds -to the current flowing through said rectifier circuit to result in a cyclically varying current flow through said cathode ray beam deflecting coil having a waveform a portion of each cycle of which is substantially linear with respect to time. the combination of an inductivity reactive control mein-4 ber connected across said inductive coupling element, and means for changing .the reactance of said control member thereby to vary the peak amplitude of the cyclically varying current flowing through said cathode ray beam deflecting coil without appreciably altering the peak amplitude of the current output of said power tube.

2. A cathode ray beam deilecting circuit in accordance with claim 1, in which said reactive control member comprises an inductor having an adjustable core element composed at least partly of magnetic material.

3. Apparatus for compensating for the e'ects of variations in the rated electrical values of the circuit components in a television scanning system of the type in which a power tube is connected to supply cyclically varying current to a cathode ray beam deilecting coil through a coupling transformer, comprising an inductive member connected in parallel with said cathode ray beam deilecting coil, and means for adjusting the inductance of said member to alter the peak amplitude of the cyclically varying current flowing through said cathode ray beam delecting coil in accordance with departures of the peak value of such current from a level predetermined in accordance with the rated electrical values of the said circuit components.

4. in a cathode ray beam deilecting circuit, a

ing current output, a transformer having its primary winding in the output circuit of said power tube, a cathode ray beam deilecting coil connected across the secondary winding of said transformer, a rectiiler tube connected across the primary winding of said transformer in parallel with said power tube, and a variable inductance element connected across at leasta portion of the secondary winding of said transformer for varying the peak amplitude of the combined current output of said power tube and said rectifier tube -as applied to said cathode ray beam dellecting coil and hence the magnitude of deflection of the cathode ray beam.

5. Apparatus for compensating for the eiects of variations of circuit components from their rated electrical values comprising means for developing a cyclically varying current a portion of each cycle of which varies substantially linearly with time, a coupling transformer, a reactive load circuit, means for feeding said current to said load circuit through said coupling transformer, an inductive member connected in parallel with the load circuit winding of said coupling transformer, and means for altering the inductance of said member so as to change the peak amplitude of the current ilowing in said load circuit while maintaining the linearity thereof.

6. Apparatus for compensating for the effects of variations of circuit components from their rated electrical values, comprising means for developing a cyclically varying current a portion of each cycle of which varies substantially linearly with time,.a load circuit which includes a reactive element, means for feeding said current to said load circuit, an inductive member connected in parallel with said reactive element, and means for altering the inductance of said member to thereby vary the peak amplitude of the current flowing through said reactive element while maintaining the linearity thereof.

7. The apparatus claimed in claim 6 comprising said inductance value.

' power tube adapted to produce a cyclically varyan adjustable magnetic element for altering the 8. In a cathode ray beam deilecting circuit having a power source adapted to produce a cyclicallyvarying current output for energizing the deecting coil of a cathode ray tube,` the combination vcomprising a transformer having its primary winding connected to receive the output from the power source and having its secondary winding connected to deliver deflecting current to the said deilecting coil, and a variable-inductance element connected in shunt with at least a portion of the transformer secondary winding to vary, with changes in the inductance value thereof, the amplitude of the deilecting current owing through the coil and induced therein through the transformer.

9. Apparatus for compensating for the effects of variations from their rated electrical values of the circuit components in a system of the'type in which cyclically varying current, a portion of each cycle of which varies substantially linearly with time, is fed to a reactive load circuit through a coupling transformer having primary and secondary windings, said apparatus comprising an inductive member connected in parallel with at least a portion of one winding of said coupling transformer, and means for altering the inductance of said member so as to change the peak amplitude of the current flowing in said load circuit.

l0. In a cathode ray beam deilecting circuit of the type in which a cyclically varying current having a Waveform wherein a portion of each cycle is substantially linear with respect to time and which wave is caused to ilow through the deilecting coil of a cathode ray tube thereby to produce substantially linear deflection of the cathode ray beam during the substantially linearly varying portion of each current cycle, the combination of an inductive coupling element, a controlled power developing means connected to supply cyclically varying current to said cathode ray beam deflecting coil through said inductive coupling element, a rectifier circuit connected across said inductive coupling element, said rectifier circuit including means for shaping the waveform of the current ilowing through the rectiiler circuit, a source of voltage variations, means for applying voltage variations from said source to said power developing means so as to produce a current output therefrom which adds to the current flowing through said rectiiler circuit to result in a, cyclically varying current ilow through said cathode ray beam deflecting coil having a waveform a portion of each cycle of which is substantially linear with respect to time, an inductively reactive control member connected across at least a portion of said inductive coupling element, and means for changing the reactance of said control member thereby to vary the peak amplitude of the cyclically varying current flowing through the deilecting coil of the cathode ray tube'without appreciably altering the peak amplitude of the current output of said power developing means.

l1. In a cathode ray beam deecting circuit having a power source adapted to produce a cyclically varying current output for energizing the deilecting coil of a cathode ray tube, the combination comprising a transformer having primary and secondary windings, the primary winding of said transformer being connected to receive the output of the power source, means for deriving from the secondary winding of said transformer deflecting current for delivery to the said 7 deecting coil, and a variable inductance element connected in shunt with at least a portion of the transformer secondary winding to vary, with changes in the inductance value thereof, the amplitude of the deecting current flowing through the coil and induced therein through the transformer.

12. In a cathode ray beam deecting circuit having a power source adapted to produce a cyclically varying current output for energizing the deflecting coil of a cathode ray tube, the combnation comprising a transformer having primary and secondary windings, the primary winding of said transformer being connected to receive the output of the power source, means for deriving from the secondary Winding of said-transformer defiecting current for delivery to the said deecting coil, and a variable inductance element connected in shunt with at least a portion of one of the transformer windings to vary, with changes in the inductance value thereof. the amplitude of the deflecting current flowing through the defiecting coil and induced therein through the transformer.

13. In a cathode ray beam defiecting circuit auaoce having a power source adapted to produce a cyclicaily varying current output for energizing the deiiecting coil of a cathode ray tube. the combination comprising a transformer having its primary winding connected to receive the output from the'power source and having its secondary winding connected to deliver detiecting current to the said deecting coil, and a, variable inductance element connected in shunt-with atleast a. portion of a winding forming a part of said transformer to vary, with changes in the inductance value thereof, the amplitude of the defiecting current iowing through the deecting coil -and induced herein through the transformer.

ANTONY WRIGHT.

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