US2628326A - Television apparatus - Google Patents

Description

Feb. 10, 1953 J. E. BRIDGES TELEVISION APPARATUS Filed March 10, 1951 Fig.1

IO K J 3 1 Rec'eive'r Circuits '3 25 2% NON-LINEAR RESISTOR 20 5%) 45 4 fV M CURRENT 2.

VOLTAGE l 12 TIME-b NON-LINEAR RESISTOR INVENTOR. JACK E. BRIDGES ATTORNEY final anode of the picture tube. has'proved quite satisfactory in the mass pro- Patented Feb. 10, 1953 UNITED STATES PATENT OFFICE TELEVISION APPARATUS Jack E. Bridges, Chicago, Ill., assignorto Zenith Radio Corporation, a corporation of Illinois Application March 10, 1951, Serial No. 214,970

4 Claims.

This invention relates to television apparatus and more particularly to such apparatus employing a cathode-ray tube having at least one electrode which requires a highpositive unidirectional operating potential relative to the cathode. Numerous arrangements are known for focusing the electron beam of a cathoderay tube. Generally, the desired focusing action may be obtained by means of a magnetic field, an elecpair of cylindrical electrodes of the same or difierent diameters operated at different unidirectional potentials. Another known electron lens arrangement comprises three focusing electrodes with the first and third of these electrodes connected together and operated at the potential of the final anode and the intermediate focusing electrode operated at a unidirectional potential intermediate that of the anode of the electron gun and the final anode. In general, to obtain the desired focusing action with an electrostatically-focused cathode-ray tube, it may be necessary to supply at least one unidirectional operating potential which is greater than v the output voltage of the direct-voltage supply or B-supply for the associated receiver apparatus, and for convenience throughout the specification' and the appended claims, the terms high voltage and high potential are employed to describe an operating voltage greater than "the B-supply voltage.

It is well known in the television art that the pulse voltage developed in the sweep-transformer primary winding of the line-frequency scanning 'systemmay be rectified and filtered to provide a-de sired high unidirectional operating potential. Systems of this type have employed a diode or other peak-rectifying device in conjunction with a storage condenser and are commonly used to supply the high operating potential .for the This expedient duction of television receivers employingmagnetically focused cathode-ray tubes, since only electrostatically focused cathode-ray tube, how- 1 ever, two different high unidirectional operating potentials may be required. While it is possible to employ a bleeder resistor in shunt with the storage condenser associated with the conventional high voltage rectifier to provide the second high unidirectional operating potential, such an arrangement is uneconomical of power and is therefore undesirable. Voltage multipliers em ployed in connection with the standard B-supply may also be employed, but such arrangements require a considerable number of additional circuit components and are therefore costly and impractical.

It is an important object of the present invention to provide a new and improved television apparatus of the typeemploying a cathode-ray tube of the electrostatically-focused type.

It is a further object of the invention to provide a simple and economical system for developing a high unidirectional operating potential for application to one of the focusing electrodes of an electrostatically-focused cathode-ray tube.

Still another object of the invention is to provide a new and improved system for developing two difierent high unidirectional operating potentials for application to the focusing electrodes of an electrostatically-focused cathode-ray tube.

Yet another object of the invention is to provide a system of this type which is readily adaptable to a conventional. television receiver and which requires a minimum number of additional circuit components.

In accordance with the invention, a television receiver includes a cathode-ray tube comprising a cathode and at least one other electrode requiring a high positive unidirectional operating 1 potential with respect to that of the cathode.

The receiver also comprises an asymmetrical voltage-wave source including an electron-dischargedevice. A series network comprising a non-linear resistor and a condenser is coupled to the electron-discharge device and is responsive to the asymmetrical voltage-wave to develop a high unidirectional voltage across the condenser. .Means are provided for applying at least a portion of the unidirectional voltage developed across the condenser between the aforementioned other electrode of the cathode-ray tube and its cathode.

In interpreting the specification and the appended claims, it must be .borne in mind that there is a fundamentaldifierence between a nonlinear resistor and other types of non-linear circuit elements, such as rectifiers, crystals, and electron-discharge devices. While non-linear and a fluorescent screen (not shown).

operating characteristics may be achieved with circuit elements of the latter type, such elements are unilaterally conductive and permit current flow in one direction only. In contrast, a nonlinear resistor of the type employed in accordance with the present invention, while possessing a non-linear volt-ampere characteristic, is bilaterally conductive and permits current flow in both directions.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further ob ects and advantages thereof, may best be understood, however, by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals indicate like elements, and in which:

Figure l is a schematic circuit diagram of a television receiver constructed in accordance with the present invention;

Figure 2 is a schematic diagram of a portion of the receiver of Figure l;

Figures 3 and 4 are graphical representations 7 useful in understanding the operation of the invention; and

Figure 5 is a schematic diagram, similar to that of Figure 2, of another embodiment of the invention.

In the receiver of Figure l, incoming composite 7 television signals are intercepted by means of an antenna it and a plied to the customary receiver circuits l I. The circuits represented by rectangle ll may be entirely conventional in construction and operation and constitute no part of the present invention. Composite video signals developed between terminals l2 and it of receiver circuits H are applied between the control grid is and the cathode if of a cathode-ray tube it which also comprises a first anode i'i, electrostaticfocusing electrodes 5 3, iii and 28, a final anode 2 5,

Fieldfrequency sweep-signals developed between terminals 22 and 23 of receiver circuits H are applied to a field-frequency magnetic-deflection coil 25 associated with cathode-ray tube it.

Line-frequency synchronizing-signal pulses from terminals 25 and 25 of receiver circuits H are applied by means of an input transformer 2? between the control grid 28 and the cathode 29 of an electron-discharge device 353, which may conveniently be of the triode type. A second electron-discharge device 3!, preferably a diode, is connected directly across the discharge path of device 30 but with opposite polarity, so that devices 39 and 3% together constitute a bidirectional electronic switch. The anode 32 of device lid is connected to a tap 33 on the primary winding of a-sweep transformer 35, and one terminal of winding 3:! is directly connected to the customary unidirectional voltage supply of the receiver, conventionally designated 3+ in the figure, so that a portion of the primary winding 34 of sweep transformer 35 is included in the output circuit of device 30. The line-frequency magneticdefiection coil 35 associated with cathode-ray tube 36' is connected between a pair of taps 3'5 and 38 on the portion of primary winding 34 which is included in the output circuit of device 38. Proferably, the location of tap-s 3'5 and 3,8 is determined in accordance with the copending application of Robert Adler et al., Serial No. 176,258, filed July 28, 1950, for Transformers, and assigned to the present assignee, in order to minimize undesired ringing currents in the line-frequency deflec- 4 tion coils and attendant velocity-modulation of the line-frequency scansions. v

A rectifier 359 and a storage condenser 59 are connected in series between the high-potential terminal it of primary winding 3% and ground,. the filament 42 of rectifier 2 being energized means of an auxiliary winding #23 magnetically? coupled to primary winding 34. Filament i2 is also coupled to the final anode 2i cathode-ray tube it by means of a resistor 5 A series network, comprising a non li uearv resistor 55 and a storage condenser it, is co. between a tap d? on primary winding 3% and: ground, beingthereby effectively connected a the portion of primary winding between and the 3+ terminal. A potentiometer ts is com nected in parallel with condenser t6, and a vari-- able tap (it on potentiometer it is connected to focusing electrode is of cathode-ray tube iii.

In operation, devices and 3t and their associated circuit components constitute a line-freduency scanning-signal generator for impressing a scanning current of substantially sawtooth waveform on line-frequency deflection coils 36. Devices 38 and 3! collectively function as a bidirectional electronic switch, and the" current through the portion of primary winding be:- tween tap 33 and 13+ increases substantially lin'-- early at a rate primarily determined by the ap-' plied unidirectional voltage and the circuit in?- ductance until such time as a negative-polarity pulse is applied between control grid 23 and oath ode 29 of device Be. When current flow in the output circuit is interrupted in this manner, substantially one-half cycle of free oscillation occurs to complete the scanning cycle.

Operation of the scanning-signal generator results in the appearance of periodic positive-polar ity pulses of extremely large magnitude across the entire primary winding 3 of sweep transformer 35. These pulses are rectified by device 39, and the high unidirectional voltage developed across condenser to is applied to final anode 2'55 by means of resistor 14. The external focusing electrodes l8 and 2% of the unipotential electron: lens may conveniently be connected together to final anode 2! so that these focusing electrodes are also energized by the voltage developed across condenser it. In practice, the operating voltage of anodes 3, 9 and 29 may be of the order of 10 kilovolts.

In a unipotential electron lens of the type schematically illustrated in Figure 1, a second high unidirectional operating potential may be applied to the intermediate focusing electrode Hi. In practice, the operating potential of intermediate focusing electrode it may be of the order of 20% of the final anode operating voltage. Such a potential is at least an order of magnitude greater than that customarily available from the conventional B+ source or B-supply. In accordance with the invention, the operating potential for intermediate focusing electrode i9 is developed by means of the series network comprising nonlinear resistor iii and condenser it effectively connected across at least a portion of the primary winding 34 of sweep transformer 35. The variable voltage-divider 48 is provided in order to permit fine control of the focusing of the electron beam of cathode-ray tube it.

As has been indicated previously, there is a fundamental difference between a non-linear resistor of the type employed in accordance with the present invention and other non-linear circuit elements such as grid-controlled electron tubes, rectifiers, and the like. Elements of the latter type are unilaterally conductive and hence may be employed to rectify any type of alternating input signals. On the other hand, the nonlinear'resistor is bilaterally conductive and has substantially no rectifying effect on an input signal of symmetrical waveform.

One type of non-linear resistor suitable for use in accordance'with the present invention is constructed of silicon carbide pressed with a suitable ceramic binder and fired at a temperature of about 1,200 degrees centigrade. Such non-linear resistors are marketed commercially by the General Electric Comp-any under the trade name Thyrite and are available in a large number of sizes and shapes. Resistors of this type do not operate in a manner comparable with that of ordinary, linear resistance elements; instead of behaving in accordance with Ohms law, Thyrite resistors have a volt-ampere characteristic in accordance with the relation (1) i=Ke where i represents the instantaneous current, e is the instantaneous applied voltage, K is a constant representing the current drawn with an applied voltage of one volt, and n is an exponent greater than unity. The constant K is dependent upon 'the resistivity and the dimensions of the particular Thyrite resistor, a typical value being of the order of The exponent n depends on various factors in the manufacturing process'and is usually at least 3.5; in some instances, 11. may be as high as 7 or more.

' In order to explain the operation of the invention, it hasbeen convenient to reproduce in Figure 2 the portion of the circuit of Figure -1 comprising the series network of non-linear resistor 45 and condenser 45. The voltage wave applied to this series network from the portion of primary winding 34 between tap ll and the 13+ terminal is graphically represented in idealized form in Figure 3, which is a plot of the applied voltage 12(12) as a function of time. In practice, the actual waveform of the voltage appearing across the portion of primary winding 34 between tap 41 and the B{ terminal is displaced slightly in a negative direction'with respect to the zero or reference axis; however, the waveform plotted in Figure 3 represents a suirlciently close approximation for purposes of circuit analysis. The applied voltage Mt) is impressed between terminals 50 and 5| of the equivalent circuit of Figure 2 and is of asymmetrical waveform, comprising periodic positivepolarity pulses each of a duration corresponding to the line-frequency retrace interval (about 14% of the line-scanning cycle in accordance with present governmental standards).

The volt-ampere characteristic of the Thyrite resistor 45 is reproduced in graphical form in Figure l. Since the applied voltage'wave is asymmetrical as shown in Figure 3, and since the volt-ampere characteristic of the Thyrite resistor is non-linear, it may readily be understood as a qualitative matter that a net unidirectional voltage is developed across condenser 36 with the polarity indicated in Figure 2, the current drawn during the 'pulse' intervals being many times greater than that drawn during the intervening intervals. At the outset, condenser 46 is completely discharged, and the application of the first positive-polarity pulse between terminals 50 and 5! results in a large current flow through condenser 55, charging the condenser with the polarity indicated in Figure 2. During the interval between the first and second pulses; the applied potential is of opposite polarity but of inuch lower magnitude, so that theresi'stance ofthe non-linear resistor increases and the condenser is only partiallydischarged through non-linear resistor 45. After' several cycles, the voltage across condenser 45 assumes'an equilibrium" value intermediate zero and thepeak amplitude-V1)" of the applied pulses. As a practical matter, the

magnitude of the voltage *Vd developed across condenser 46 may be of the order of ofthe peak amplitude Vp of the appliedp'ulses.

More rigorously, the magnitude of the'unidirectional voltage developed across'condenser 46 may be determined from a mathematical'consideration of the volt-ampere characteristic set forth by Equation 1. For a conditionjof equilibrium, the electrical charge acquiredb'y' 'the condenser during each pulseinterval must equal the charge lost during the" remainder of the operating cycle. This condition may be expressed by the equation where for (4) fotti and for

(6) 1 trttz Performing the indicated operations and reducing to simplest terms,

1: i t l E n io) +1 Under the assumed condition that the pulseduration is about 14% of the operating cycle,

Combining Equations 8 and '7 and'assuming an exponent n of 5 for the particular Thyrite resistor, it is apparent that the-'maximum'unidirectional voltage obtainable across condenser '48 is of the order of -40%'of th'e'peak amplitude of the positive pola'rity pulses. l\/Ioreover,'"the magnitude of the unidirectional voltageapparlinear resistor or a conventional'rectifier of the,

unilaterally conductive type. The Thyrite re-a sistor diifers from an ordinary resistance element in the exponential nature of its volt-ampere characteristic and from a conventional rectifier in its property of symmetrical bilateral conduc.- tivity. Because of the non-linear variation 9;

current with voltage, a unidirectional output voltage may be developed. from an. asymmetrical alternating input voltage. Because of the prop erty of bilateral conductivity, the maximum unidirectional voltage which may be developed in this manner is restricted to so hewhat less than one-half the peak voltage of the applied asunmetrical wave. This limitation is not objectionable, however, in a system such as that s own and described in connection with Figure l, ere the desired unidirectional operating potential is much smaller than the peak amplitude of the available asymmetrical voltage-Wave.

The use of a non-linear resistor such as Thyrite for developing a high unidirectional operating otential has several advantages over conventional high-voltage supply systems. In t first place, the Thyrite resistor s a simple twoterminal element, and no auxiliary transformer winding is required for filament ener ation as in the case of systems employing a diode recti Thyrite resistors are also somewhat less expensive, more durable, and require less frequent re placement, as a general rule, than suitable diod rectifier tubes. Moreover, the add t n of i circuit comprising Thyrite resistor so and corn denser ilfi results in an additional power dissipation comparable to that imposed by known arrangements for obtaining high voltage from the sweep system; consequently, the system of He present invention has the advante e over the e of a bleeder resistor in conjunction with the high-voltage supply for the final anode that a considerably smaller additional load is placed on the sweep circuits. The V ge regulation ootainable with the system of the present invention is within 19%, a figure which is quite coe; in connection with high-voltage supplies for electrostatic focusing.

In order to avoid the necessity for maintaining stringent tolerances in the mass pr duction of television receivers, it is desirable to provide means for varying the operating pots 1 applied to at least one of the focusing electrodes. Moreover, the provision of a variable high-voltage supply also permits the consumer to make fine adjustments in the beam focus under operating conditions.

In the system or a variable voltage-divider such as pets 48 is connected in shunt with condo; s a variable tap on the poten iometer is connected to one of the focusing electrodes. The objective may also be achieved in the manner illustrated schematically in Figure 5, wherein nonlinear resistor 35 is provided "-i a slip con tact EEG, and a resistor 81' ha of the order of 168 megohins or in par llel with comm er 2:; ment, the positive terminal of ,condenser 45 is directly connected to focus ng voltage developed across co varied by varying the position of elder so on Thyrite resistor ie; movement of the slider changes the voltage ratio between the ac ve per tion of non-linear resistor resist In practice, focusing electrode i=3 may draw sunlcient beam current to provide the desired e. ective resistance across condenser so that no external circuit element corresponding to resistor is required.

While the invention has been shown described in connection W h an auxiliary highvoltage supply system for iurnishing an operating potential intermediate that of the B-supply and that applied to the final anode of the picture tube, it is contemplated that the present invention also be employed to advantage in furnishing high unidirectional voltage for other operating electrodes of the picture tube. As has been already explained, the maximum unidirectional voltage obtainable by employing a nonlinear resistor is somewhat less than one-half the peal; a plitude of the available asymmetrical voltage .a-ve. Since the peak amplitude of the pulses developed. in the sweep transformer of a conventional television receiver is of the order of from 10 to 12 kilovolts, and since the required operating potential for the final anode of present cathode-ray tubes is of the same order of magnitude, it is apparent that the system of the invention is not presently suitable for providing the final-anode operating voltage. However, in he event that an asymmetrical voltagewave or" larger amplitude should become available, or ii" future developments should include a prac ical television tube operable with a finalanode voltage of the order of 5 kilovolts or less, it is apparent that a non-linear resistor and a condenser may be employed in accordance with the invention to provide the desired operating voltage for the final anode.

In the system shown and described in connection with Figure l, the sweep transformer 35 is or" the autotransformer type, employing judiciously positioned taps on a single transformer winding. It is of course within the scope of the present invention to employ a sweep transformer having one or more separate secondary windings in place of the autotransformer of Figure 1. Thus for example, the series network comprising Thyrite resistor :35 and condenser ill may be connected across a separate secondary winding which is magnetically coupled to the primary wi ing. In an arrangement of this type, the series network is eiiectively connected across at least a portion of the primary Winding, within the meaning of the appended claims.

It is not essential for the purposes of the present invention that a sweep-signal generator of the type shown in Figure 1 be employed. Other types of sweep-signal generator may be substituted for that shown in Figure 1 with equally good results. In any event, it is essential that the asymmetrical voltage-wave source comprise an electron-discharge device to which the series network comprising the non-linear resistor and the condenser is coupled. This electron-discharge device may be either a sawtooth-current generator as in the system of Figure l, or a sweep amplifier in the event that the sawtooth wave is developed in a preceding stage. Indeed, it is within the invention in its broadest aspects to employ an entirely separate asymmetrical voltagewa-ve source which performs no other function than that of supplying power to the series network. comprising the non-linear resistor and storage condenser.

Thus, the present invention provides a new improved high-voltage supply system which is particularly useful to furnish a desired high unidirectional operating potential for a focusing el ctrode of an electrostatically-focused cathoderay tube. The system is simple, reliable and inexpensive and imposes but a nominal increase in the power dissipation of the apparatus. The obtainable voltage regulation is well within commercially accepted limits.

While particular embodiments of the present invention have been shown and described, it is apparent that various changes and modifications may be made, and it is therefore contemplated in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

I claim:

1. In a television receiver: a cathode-ray tube comprising a cathode and at least one other electrode requiring a high positive unidirectional operating potential with respect to that of said cathode; an asymmetrical voltagewave source including an electron-discharge device; a series network comprising a bilaterally conductive nonlinear resistor and a condenser coupled to said device and responsive to said asymmetrical voltage-wave to develop across said condenser a high unidirectional voltage; and means for applying at least a portion of said unidirectional voltage between said other electrode and said cathode.

2. In a television receiver: a cathode-ray tube comprising a cathode and at least two focusing electrodes each requiring a different high unidi rectional operating potential with respect to that of said cathode; a scanning-signal generator comprising an electron-discharge device having an input circuit and an output circuit; a sweep transformer having a primary winding- 2, portion of which is included in said output circuit; a rectifier and a condenser effectively connected in series across said primary winding; a series network comprising a bilaterally conductive nonlinear resistor and a condenser effectively connected across at least a portion or said primary winding; means for impressing an input signal on said input circuit to induce a periodic asymmetrical pulse -voltage wave in said primary windins, whereby different high unidirectional voltages are produced across said respective condensers; means for applying one of said unidirectional voltages between one of said focusing electrodes and said cathode; and means for applying at least a portion of the other of said unidirectional voltages between the other of said focusing electrodes and said cathode.

3. In a television receiver: a cathode-ray tube comprising a cathode and at least two focusing electrodes each requiring a diiferent high unidirectional operating potential with respect to that of said cathode; a scanning-signal generator comprising an electron-discharge device having an input circuit and an output circuit; a sweep transformer having a primary winding a portion of which is included in said output circuit; a rectifier and a condenser effectively connected in series across said primary winding; 2, series network comprising a bilaterally conductive nonlinear resistor and a condenser effectively connected across at least a portion of said primary winding; means for impressing an input signal on said input circuit to induce a periodic asymmetrical pulse-voltage wave in said primary winding, whereby different high unidirectional voltages are produced across said respective condnsers; means for applying one of said unidirectional voltages between one of said focusing electrodes and said cathode; and means including a variable voltage-divider for applying a variable portion of the other of said unidirectional voltages between the other of said focusing electrodes and said cathode.

4. In a television receiver: a cathode-ray tube comprisin a cathode and at least two focusing electrodes each requiring a different high unidirectional operating potential with respect to that of said cathode; a scanning-signal generatorcomprising an electron-discharge device having an input circuit and an output circuit; a sweep transformer having a primary winding a portion of which is included in said output circuit; a rectifier and a first condenser effectively connected in series across said primary winding; a series network comprising a variable bilaterally conductive non-linear resistor and a second condenser eirectively connected across at least a por tion of said primary winding; means for impressing an input signal on said input circuit to induce a periodic asymmetrical pulse-voltage wave in said primary winding, whereby difierent high unidirectional voltages are produced across said respective condensers; means for applying the unidirectional voltage appearing across said first condenser between one of said focusing electrodes and said cathode; and means for applying the unidirectional voltage appearing across said second condenser between the other of said focusing electrodes and said cathode.

JACK E. BRlDGES.

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

UNITED STATES PATENTS Number Name Date 1,094,733 Lyle Apr. 28, 1914 2,152,016 Baesecke Mar. 28, 1939 2,255,485 Dome Sept. 9, 1941 2,261,795 Chittick Nov. 4, 1941 2,434,196 Cawein Jan. 6, 1948 2,458,891 Boyle Jan. 11, 1949 2,459,319 Hansell Jan. 18, 1949 2,555,147 Meag-her May 29, 1951 OTHER REFERENCES Industrial Electronic Control by W. D. Cockrell, published in 1944 by McGraw-I-Iill Book 00., Inc., N. Y., pages 8889 (Fig. 6)

Chamber's Technical Dictionary by C. F. Tweney and L. E. 0. Hughes, published in 1944 by the MacMiLlan 00., page 582.

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