US2440786A

US2440786A - Cathode-ray beam deflecting circuits

Info

Publication number: US2440786A
Application number: US492868A
Authority: US
Inventors: Otto H Schade
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1943-06-30
Filing date: 1943-06-30
Publication date: 1948-05-04
Anticipated expiration: 1965-05-04

Description

C. H. SCHADE CATHODE RAY BEAM DEFLECTING CIRCUITS Filed June 30 1945 A TTOBNK Lw/f6 1N VEN TOR. an@ H. Salad@ BY May 4, 1948.

"ETL- mtl occur and in order that the dimensions of Patented May 4g, i948 2,440,186 cA'rHonE-RAY BEAM DEFLECTING CIRCUITS Otto H. Schade, West Caldwell,.N. J.. assignor tov Radio Corporation of America,

Delaware a corporation of Application .lune 30, i943, Serial No. 492,868

(Cl. F75-335) 2 Claims.

This inventionrelates to an improvement in cathode ray beam defiecting circuits, and more particularly, in circuits used for electromagnetically deflecting acathode ray beam in such a manner that a high degree of linearity of deflection and stability of amplitude of deflection may be maintained.

Where a cathode ray tube is used to produce luminous indications, it is frequently desirable to deflect the cathode ray beam in the tube at a predetermined constant rate of speed across the screen of the tube. This is'particularly true in the case of television receivers where the linearity of deection should be maintained at the highest possible degree in order that no distortion will be present in the produced television picture. It is also desirable that the degree of deflection or the deection amplitude be maintained constant in order that distortion will not the produced image will not be altered.

It is well known that a cathode ray beam may be deflected by electrostatic or electromagnetic fields, and the latter form of deflection is the type with which the present invention is concerned.

Various circuit arrangements have been provided for improving the linearity of beam deection in electromagnetic deflection circuits, but in most instances true linearity is not completely obtained, with the result that the rate of deflection of the cathode ray beam across the screen is not absolutely uniform throughout the entire deection interval.

By means of the present invention, a circuit arrangement has been provided whereby a high degree of linearity maybe accomplished in a cathode ray beam deection circuit. It is also possible by means of the present invention to maintain the amplitude of deflection substantially constant irrespective of changes in operating conditions and variations in the voltages applied to the tubes as may occur in normal operation of the system.

The purposes of the present invention are in general accomplished by utilizing degenerative feedback in the deflection system, the system having inherently relatively small wave form distortion, with the result that a very high degree of linearity of deflection will result. By the same arrangement it is also possible to maintain the amplitude of deflection substantially constant in spite of operational drifts that may occur during the normal operation of the system. Through the use of the present invention, it is also possible to maintain a high degree of linearity of deflection over a considerable range of frequencies, and accordingly the present invention may be used in a wide variety of apparatus wherein cathode ray tubes are employed.

The present invention may also be applied to deflection circuits wherein the deflection tubes are operated in either class A or class B.

It is, therefore, one purpose of the present invention to provide a circuit for electromagnetically deflecting a cathode ray beam in which a high degree of linearity of deflection may be maintained.

Another-:purpose of the present invention resides in the provision of a circuit for electromagnetically deflecting a cathode ray beam in which the amplitude of deflection may be maintained substantially constant irrespective of normal operational changes in the system.

Still another purpose of the present invention resides in the provision of a circuit for electromagnetically deecting a cathode ray beam in which a high even though low percentages of harmonic distortion may occur in the various tubes used in the deflection circuit.

Still another purpose of the present invention resides in the use of degenerative feedback in a circuit for electromagnetically defiecting a cathode ray beam thereby to improve the linearity of deection and to maintain the amplitude of deflection stable.

A still further purpose of the present invention resides in the application of degenerative feedback in a cathode ray beam deflecting circuit where the-deiection tubes are caused to function in either class A or class B operation.

Still another purpose of the present invention resides in the provision of means in a circuit for electromagnetically deiecting a cathode ra? beam wherein a potential drop is produced as a result ofthe ow of the beam deflection current, the produced potential drop being utilized in a degenerative manner to improve linearity of deection and to maintain the amplitude of deection uniform.

Various other purposes and advantages of the present invention will become more apparent to those skilled in the art from the following dethe drawings, and particdegree of linearity'is produced ularly to Figure 1 thereof, there is shown an electron discharge tube I which includes a, cathode, a control electrode and an anode. The cathode of tube I IJ is connected directly to ground or a point of fixed potential, whereas the control electrode is connected to one of the input terminals I2 in order that a voltage variation of the desired wave form may be applied thereto. The anode of tube -l0 is connected,l by way of load resistor l'6, to positive terminal I4 (to which a source of positive potential is applied). The anode of tube I0 is also connected to ground by way of a resistance-capacitance circuit including resistance I8, coupling condenser 20 and a further condenser 22. The two condensers 20 and 22, as well as the resistance I 8, are connected in seriesto form the resistance-capacitance circuit.

The control electrode of tube ID issupplied with a, series of negative impulses, as represented by the curve 24 in the drawing. These impulses occur at a frequency corresponding to the desired deflection frequency. Tube I0 is normallyv conducting, but is intermittently rendered substantially non-conducting by the succession of negative impulses applied to the control electrode thereof. During thesel non-conducting intervals, the series condensers and 22 are charged through resistances I6 and I8, and are subsequently discharged by the tube I 0 during its conducting intervals. As a result, a voltage Variation is produced at the junction of the series condensers 20 and 22 similar to that represented by the curve 26.

The resistance-capacitance circuit forms an integrating circuit responsive to the potential variations at the anode of tube IIJ, these potential variations corresponding to the applied pulse series 24 except that their polarity is reversed. The capacitance 20 should preferably be chosen to have a value equal to about twice the capacitance of the condenser 22. With such an arrangement the linearity of the sawtooth shaped .voltage variations 26 present at the junction of the condensers 2D and 22 can be made very good if only a relatively small percentage of the full anode voltage is used.

'I'he voltage variation represented by the curve 26 is applied to the control electrode of tube 36, which includes at least a cathode, a control electrode and an anode, but Which is preferably of the screen grid type. The cathode 32 of the tube 30 is connected to ground by way of cathode resistance 34, and the anode of tube 30 is connected to the positive terminal I4 by Way of anode load resistance 36. When the potential of the control electrode of tube 30 is varied by the voltage variation appearing at the junction of condensers 20 and 22, a corresponding voltage Variation of sawtooth wave form will be produced at the anode of tube 30, as indicated by the curve 39. These voltage variations are then applied to the control electrode of a power deflection tube 40 by way of coupling condenser 38. The control electrode of tube 40 is connected to ground by way of grid resistor 42. The cathode of tube 40 is connected to ground by way of cathode resistance 44, in order that the potential drop thereacross will produce the desired relative potential between the cathode and control electrode of the tube. It is preferable that some degeneration be present in the tube and, as a result, no by-pass condenser is connected in parallel with the cathode resistance 44.

The power deflection tube 40 is preferably of the beam power type, and includes a cathode, control electrode, screen electrode and anode. The screen electrode may be connected directly to the positive terminal I 4, whereas the anode of tube 40 is connected to the positive terminal by way of the primary winding 46 of transformer 48. A damping resistance 50 and condenser 52 are connected in series across the primary winding 46 of the transformer. The transformer 48 is also provided with a secondary winding 54, one terminal of which is connected to ground, and the other terminal of which is connected to a contact point 56. The anode of tube 40 is connected to another contact point 58. and switch arm 60 is provided for cooperating selectively with one or the other of contact points 56 or 58.

The dellecting coil or coils 62 for electromagnetically dellecting the cathode ray beam are then connected between the movableY switch arm 6U and the cathode of tube 30, with condenser 64 interposed in the cathode connection. By means of the switch arm 6D, the deiiecting coil 62 may then be energized directly from the anode of tube 40, or it may be energized through the transformer 48 from the voltage induced in the secondary winding 54.

When voltage variations of sawtooth wave form, such as represented by the curve 39, are applied to the control electrode of tube 40, the desired current variation in the anode circuit of tube 4|] is produced such that substantially linear deflection of the cathode ray beam results.

By reason of the fact that the deflection coil current flows through the resistance 34 in the cathode circuit of tube 30, a negative feedback voltage is produced by a corresponding potential drop across resistance 34. Accordingly, the current in the plate circuit of tube 30 is affected both by the voltage variations applied to the control electrode of tube 30 and by variations in the potential drop across the cathode resistance 34. These two voltages add in phase but with opposing polarity, i. e., in a degenerative sense. When degenerative feedback is provided in this manner, the circuit shown in Figure 1 will operate to deflect the cathode ray beam at substantially any scanning frequency, and a high degree of linearity of deflection will result. Furthermore, the amplitude of deflection will be main*- tained substantially constant.

For most efficient operation, it is desirable that the system inherently have good linearity since departure from' strict linearity, when corrected by degeneration, can only be improved by the same percentage as the gain or degree of amplication is reduced. In order, therefore, to not excessively reduce the gain of the deflection system, it is preferable that the system have inherently fairly good linearity so that a minimum amount of degenerative reaction is necessary in order` that the desired high degree of linearity of deflection may be accomplished.

Before feedback can be effective to reduce or compensate for distortion, it is necessary that the tube into which the feedback voltage is injected, as well as all tubes following that tube, be in an operating condition during the time that the feedback is to be effective. Accordingly, if the degenerative feedback shown in Figure 1 is to be effective over the entire deection stroke, then it is necessary that

tubes

30 and 40 be operated in class A operation. When class AB or class B operation is employed, i. e., when the tube is inoperative during a portion of the cycle, naturally the tube is inoperative during the cut-off period and hence cannot reduce distortion during this period. The circuit shown in Figure l, therefore?, employs tubes with class YA operation, and when degenerative feedback is employed such as shown in the figure, a high degree of linearity of deflection may be maintained and the degree or amplitude of deilection may be held substantially constant.

A modification of the present invention is shown in Figure 2 in which a modified form of degenerative feedback is employed. In this circuit, a tube is provided having at least a cathode, a control electrode and an anode, the tube being preferably of the beam power type. A condenser 12 is provided, one plate of which is connected to input terminal 16, the other plate being connected to ground -by way of an adjustable resistance 16. Thecondenser 12 is the discharge condenser on which a rising sawtooth voltage is generated from a preceding tube (not shown), so that a voltage variation of substantially sawtooth wave form. as represented by curve 15, is present at the input terminal 1B, and this voltage variation is applied 'to thevcontrol electrode of tube 10 by way of coupling condenser 18. The control electrode of tube 10 is connected to ground by grid resistor 80, and the cathode of tube 10 is also connected to ground by cathode resistance 82, this resistance being by-passed by condenser 89.

The anode of tube 10 is connected to a positive terminal 86 (to which a source of positive potential is applied) by way of series connected inductance 88 and resistance 90. The resistance 90 has 'a value generally several times the resistance of the deec'ting coils, and may be eliminated if the resistance of the choke coil 88 is suillciently high. The defiectng coils 92 for electromagnetically deflecting the cathode ray beam are connected between the anode of tube 10 and the junction of condenser 12 and resistance 16 by way of a condenser 96. This condenser 94 is preferably of relatively large capacity and may be of the electrolytic type.

A controlled damping tube or inverted tube 96 is also employed, and this tube includes at least a cathode, a control electrode and an anode. The cathode of tube 96 is connected directly to the anode of tube 10, while the anode of tube 96 is connected to the positive terminal 86 by way of adjustable resistance or potentiometer 98. The anode of tube 96 is also connected to a single-pole double-throw switch |00 in order that the anode may be connected selectively (1) to the junction of condenser 94 and defiecting coils 92, and thence to resistance 16 by way of low alternating current impedance or condenser 94, or (2) to ground by way of condenser |02.

The tube 96 is preferably of the beam power type, in which case it also includes a screen electrode to which an adjustable potential may be applied by means of the potentiometer |04. The resistance element of this potentiometer is connected between the positive terminal 86 and ground, and the movable contact of the potentiometer is connected to the screen electrode by resistance |06. A decoupling condenser |08 is connected between the screen electrode and ground.

The control electrode of tube 96 is connected to its cathode by means of two series connected parallel resistor-condenser combinations, the rst of which includes resistance |0| and condenser H2, and the second of which includes resistance H4 and condenser IIS.

With the circuit arrangement as described,

when a voltage variation of sawtooth wave form is applied to the control electrode of the tube 10, a current variation is produced in the deecting coils to electromagnetically deflect the cathode ray beam in a substantially linear fashion. Inasmuch as a portion of the current in the defiecting coils, depending on the position of switch |00, must flow through the resistance 10, a potential drop is produced thereacross which is also effective to modulate the potential of the control electrode of tube 10. This provides degenerative feedback which is fully eil'ective and caused by the currents of tube 10 and. tube 96 when the switch arm |00 is connected to the condenser |02. The resistance 0| serves then as an isolation resistor, providing a direct current path for the beam centering current. The resistor |0| may be replaced by an appropriately chosen choke. Partial feedback results when the switch arm |00 is moved into contact with the junction ofl the deilecting coils 92 and the condenser 94 (as shown ,y

tions is shown and described, for example, inV

Schade U. S. Patent No. 2,382,822, `issued on August 14, 1945. Linearity of the deection can in part be controlled by the potentiometer |04, since an adjustment of this potentiometer determines the amount of current permitted to passv through tube 96. The adjustable resistance 98 is effective for centering the cathode ray beam on the screen.

The degree of degeneration or inverse feedback can be regulated by an adjustment of resistance 16 since an increase in the size or value of resistance 16 naturally increases the degree of degeneration. If the degree of degeneration is increased, the amplitude of deiiection is decreased, with the result that a variation in size of the scanned raster may be controlled by varying the value of the resistance 16. Conversely, if the value of resistance 16 is decreased, the degree of degeneration is decreased and the size or amplitude of deflection is correspondingly increased.

Accordingly, by reason of the particular circuit arrangements and the degenerative feedback provided therein, it is possible to maintain excellent linearity for very large deflection size or amplitude variations. This is a result which has heretofore been difdcult, if not impossible, to achieve. When the potentiometer |04 is properly adjusted to produce good linearity without feedback, a very high degree of linearity and stability may then result by reason of the degenerative cfeedback, and the degree oi degenerative feedback may then be utilized to control the size or amplitude of deection.

Since a damping or controlled inverted tube 96 is included in the circuit shown in Figure 2, it is possible that tube 10 may be operated as class AB if desired, although the circuit arrangement shown and described is most effective for class A operation of the tube.

Although the circuits shown in Figures 1 and 2 have been described somewhat indetail. it is Having nowdescribed my invention, what I I claimas new and desire to have protected by Letters Patent is:

1. A cathode ray beam deecting Icircuit cornprising means for generating a voltage variation .of substantially saw tooth Waveform, an electron discharge tube having at least a cathode, a control electrode and an anode, means 'including an impedance for maintaining the anode positive with respect to the cathode, a grid resistance for connecting the control electrode to a point of fixed potential, a condenser and an adjustable resistance connected in series between the control electrode and the point of fixed potential, means to apply the generated voltage variation oft' saw tooth waveform to the control electrode of said tube to produce corresponding potential variations at the anode thereof, a cathode ray beam deiecting coil, means to couple the cathode ray beam deecting coil to the anode of said tube so that current variations will be produced therein in response to the potential variations present at the anode of said tube, an inverted discharge tube effectively connected in parallel with the deiiecting coil, and means including a condenser to direct at least a portion of the deflecting coil current variations through the adjustable resistance associated with the control electrode of said tube whereby a potential variation will b`e produced across said adjustable resistance, the potential variations being in phase with the generated voltage variations of saw tooth waveform and having a polarity opposite to that of the generated voltage variations.

2. A cathode ray beam deflecting circuit comprising means for generating a voltage variation of substantially saw tooth waveform, a deflection power tube having at least a cathode, a control electrode 4and an anode, means including an impedance to maintain the anode positive with respect to the cathode, means including a resistance to connect the control electrode of said tube to a point of xed potential, a condenser and an adjustable resistance connected in series between the control electrode and the point of fixed potential, means to apply the generated voltage variations to the control electrode of said tube to produce corresponding voltage variations at the anode thereof, a cathode ray beam deflecting coil, means including said adjustable resistance to connect the deflecting coil between the anode off said tube and the point of fixed potential so that current variations are produced in said deilecting coil and in said adjustable resistance in response to the voltage variations at the anode of said tube, an electron discharge path eil'ectively connected in parallel with said deflecting coil, and means to alter the impedance of the electron discharge path in accordance with the waveform of the potential variation at the anode of the deflection tube, the potential variations caused 'by the current variations in said adjustable resistance being effective to modulate the potential of the control electrode of said deflection tube, the potential variations being in phase with and degenerative with respect to the degenerated voltage variations of substantially saw tooth waveform.

OTTO H. SCHADE.

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

UNITED STATES PATENTS Number l Name Date 1,519,211 Martin Dec. 16, 1924 1,925,160 Whitelock Sept. 5, 1933 2,085,409 Bedford June 29, 1937 2,147,114 Stocker Feb. 14, 1939 2,167,368 Meyers July 25, 1939 2,168,403 Geiger Aug. 8, 1939 2,241,762 Blumlein May 13, 1941 2,251,851 Moore Aug. 5, 1941 2,254,031 Faudell Aug. 26, 1941 2,280,733 Tolson Apr. 21, 1942 FOREIGN PATENTS Number Country Date 424,221 Great Britain Feb. 18, 1935 515,158 Great Britain Nov. 28, 1939 OTHER REFERENCES Radio Engineering, by F. E. Terman, 2nd ed., 3rd impression, 1937, published by McGraw-Hill Book Co., Inc., pages 253, 254 and 255.

Radio Engineers Handbook, by F. E. Terman, 1st ed., 3rd impression, 1943, published by McGraw-Hill Book Co., Ine., pp. 398, 399 and 400.