US2101520A - Oscillator for use with kinescope deflecting circuits - Google Patents

Description

0 2 5 1 0S 1 H 2U c R I C G N I T C m L Am D EE m N 0% Sm LI OK mm Aw W S U R O F R O T A L L m 7 3% 9 1 pl 9 e D Filed Feb. 27, 1952 HORIZONTAL .DEFL E C TION CIRCUIT VOLTAGE WAVE CURRENT WAVE 1NVENTOR. Mllzam 1112716021, JusZinRDun can,

lqo 00 Tu ENS Soqooon TIME WAVE VOLTAGE WAVE VOLTA GE WA VE G P VOLM E LATE28 PLATE VOLT/7G5 PLATE CURRENT RADIO RECEIVER ?atenteii Dec. 7 1932 UNITED STATES Y OSCIILATOR FOR USE WITH KINESCOBE DEFLECTING CIRCUITS I William A. Tolson, Erlton, and Justin E. Duncan,

Camden, N. 3., assignors to Radio Corporation of America, a corporation of Delaware Application February 27, 1932, Serial No. 595,484

18 Claims.

Our invention relates to improvements in television systems and, more particularly, to an improved method and apparatus for synchronizing operating action at a receiving station with that at a transmitting station.

Television receiving systems of the general character as that disclosed in the copending application by Arthur W. Vance, Serial No. 544,959, filed June l7, 1931, and assigned to the Radio Corporation of America, comprise a cathode ray tube with horizontal and vertical ray-deflecting coils, a horizontal deflection system for causing a saw-tooth current wave at the desired linescanning frequency to pass through the horizontal ray-deflecting coils, and a vertical deflection system for causing a saw-tooth current wave at the desired framing frequency to pass through the vertical ray-deflectingcoils.

For the purpose of synchronization, a dynatron oscillator is utilized to generate sharpvoltage peaks in the plate circuit thereof, and its oscillation frequency is locked in step with operating action at the transmitting station by transmitted synchronizing impulses which are applied to the grid circuit of the dynatron. The tips of the voltage peaks referred to, which occur at the ends of the scanning periods, are utilized to drive the horizontal deflection system which includes a condenser discharged by a tube having its grid circuit supplied from the plate circuit of the dynatron. The condenser-discharge tube is so biased that it draws plate current only during the occurrence of the tips of the voltage peaks referred to.

While these systems have been found to lend themselves to satisfactory operation, a distinct operating disadvantage thereof resides in the fact that the frequency of oscillation of the dynatron oscillator is directly controlled by the applied plate and screen-grid voltages. Relatively small variations in supply voltages, therefore, are efiective to change the frequency suficiently to throw the system out of synchronism.

With the foregoing in mind, it is one of the objects of our invention to provide an improved television system of the character referred to embodying an oscillator circuit which not only generates a sharply-peaked output voltage wave, but which also maintains its required frequency of oscillations independently of occurring variations in the supply voltages over a range usually met with in practice.

Other objects and advantages will hereinafter appear.

In accordance with our invention, for hori- (Ci. 250-36) I zontal deflection of the cathode ray, a sharplypeaked output voltage wave is generated by employing a coupled oscillator with a resistance and a condenser in the grid circuit, the capacity of the condenser being such that the charge which 5 it stores up during the first oscillation is effective at substantially the completion thereof to block the tube against further oscillations by supplying a. bias potential to the grid more negative than the cut-oi! potential.

At this point in the operating cycle, the resistance is effective to provide a leakage path for the charge, the rate of leakage, however, being such that the period 'of time elapsing before the bias becomes sufficiently less negative that 15 it reaches a. magnitude approximating that of the cut-oil potential or slightly below it, is of the order of ten to twenty timesthe period of the first, single oscillation, the sum of the two periods being equal to a scanning-line period. 20 There occurs, therefore, only a single, sharplypeaked voltage wave once during each scanningline period, and these are utilized to generate a saw-tooth current wave at the scanning-line frequency. 25

For vertical deflection of the cathode ray, 9. similar oscillation circuit is embodied in the vertical deflection system for generating a saw-tooth current wave at the framing frequency.

For the purposes of synchronization, the ca- 30 pacity of the blocking condenser and the value of the grid-leak resistance in each circuit are such that, at the end of the operating cycle, the bias on the grid is still slightly more negative than the bias necessary for cut-oil, at which time 35 a received synchronizing or framing impulse applied to the grid is effective to bring the bias at least to or slightly more positive than the cutoff potential. In this manner, the received synchronizing and framing impulses are effective to 40 cause the operating cycles to begin at the same point at the end of each scanning-line period or each frame, as the case might be.

Our invention resides in the system and method of operation of the character hereinafter de- 4 scribed and claimed.

For the purpose of illustrating our invention, an embodiment thereof is shown in the drawing,

wherein Figure 1 is a diagrammatic view of a television 50 receiving system embodying our invention; and

Fig. 2 is a graphical illustration of the principle of operation in Fig. 1.

The particular embodiment of our invention shown in Fig. 1 comprises a cathode ray tube II having its control-grid circuit supplied with picture signals by way of a connection ll terminating at an adjustable contact i2 associated with a resistance I 3, the latter being connected across the output of a suitable radio receiver l4.

The cathode ray I5 is caused to scan the usual fluorescent screen I6 by electromagentic coils I! for deflecting the ray horizontally, and by electromagnetic coils ill for deflecting the ray vertically. For this purpose, the horizontal deflection circuit shown generates a saw-tooth current wave at a suitable line-scanning frequency, for example, 1200 cycles, and supplies this wave to the coils H. In like manner, the vertical deflection circuit shown generates a saw-tooth current wave at a suitable framing frequency, for example, 20 cycles, and supplies this wave to the coils I 8.

The horizontal deflection circuit includes an oscillator l9 comprising an electron tube 20 and a transformer 2| providing an inductive coupling between the plate and grid circuits. A blocking condenser 22 is connected as shown between the grid of the tube 20 and the grid winding 23 of the transformer. An adjustable resistance 24 provides a leakage path to ground for the electrical charge stored in the condenser 22, as will hereinafter more fully appear.

The manner of operation of the oscillator cir-' cuit l9 will now be explained, with reference to Fig. 2. At the start of the operating cycle at the time t, the plate current increases, and the polarity of the grid winding 23 of the oscillation transformer is such that the grid is then driven positive. This action is effective to increase the plate current still further until a condition of saturation is reached at the point x, after which the plate current takes the path along the curve from the point x to the point 1/. From the point the plate current decreases almost instantaneously to zero, by reason of the fact that, at the instant the plate current begins to decrease at the point 1/, the polarity of the grid is reversed by the action of the transformer windings 2| and 23 with respect to each other. This drives the grid almost instantaneously to a negative potential far below that necessary for cut-oil, that is, to the relatively large negative potential 2.

The potential 2 is a transient potential, due to the sharp decrease of plate current, and the grid potential, therefore, returns along a transient path a, to a value El corresponding to the negative charge stored in the condenser 22 from the time t1 to the time is. That is, from the time ii to the time is, the grid draws current and, during this period, a negative charge is stored in the condenser 22. The charge stored by the condenser is not appreciably affected by the resistance 24 because the latter is relatively high compared to the resistance between the grid and cathode. E2 is the negative voltage required on the grid to prevent flow of plate current. Therefore, the difference between El and E2, or E3, isthe voltage by which the negative charge on the grid side of the condenser 22 must be reduced before the plate can again begin to draw current to start the next cycle of operation.

The time, is minus t4, required for this discharge, which is represented by the line 25, is determined by the ratio existing between the value of the resistance 24 and the capacity of the condenser 22. i

It will be assumed that, for correct operating action, each cycle is to start exactly at the point 26. In actual practice, it has been found expedient to so adjust the resistance 24 that the charge,

at the potential E, stored in the condenser leaks off in a manner represented by the dash line 21. It will thus be seen that, at the time is, the negative potential on the grid has not quite reached the value E2. At this instant, however, a sharp synchronizing impulse 28, impressed on the grid circuit, is effective to instantaneously raise the potential on the'grid at least to or even slightly past the potential represented by the point 26, whereupon conditions will again be such that the plate can draw suflicient current to initiate the next succeeding operating cycle.

During the period t to is, which is determined primarily by the natural period of the plate and grid windings of the oscillation transformer 2|, the plate draws current.

The period t to s is that required for a complete operating cycle, and equals a scanning-line period in the horizontal deflection circuit and a picture-frame period in the vertical deflection circuit, or, in other words, equals the period of a saw-tooth current wave.

From the foregoing, it will be seen that, by exciting the grid circuit from the plate circuit, and

by using the proper values of capacity and resistance, the oscillator is permitted to make only one complete oscillation during each complete operating period occupying the time t to ts. Only a single voltage peak, therefore, is developed. An electrical charge is stored in the condenser 22 during the period h to is, and the stored charge is utilized at the end of this period to block the circuit against further oscillation during the pe riod t; to ts of the cycle. The charge gradually leaks ed by way of the resistance 24 during the period ii to is to a point somewhat removed from the point 26, and the received synchronizing impulse 28 is utilized to elevate the potential to the point 26, or to a point slightly beyond the same, whereby the circuit is again free to oscillate once.

By reason of the action just described, a voltage wave, similar to that designated by the reference numeral 29, appears on the grid of the tube 20, and positive voltage peaks 30 and negative voltage peaks 3| appear on the grid of a tube 32 having its grid circuit inductively coupled by the transformer winding 33 to the grid and plate circuits of the tube 20. The relation of the polarities of the windings 33 and 23 is such that the voltage on the grid of the tube 32 is in phase with that on the grid of the tube 20. The tube 32 operates to eliminate the negative peaks 3|, the positive peaks 30 in the grid circuit appearing in the plate circuit as negative peaks 34. A

reverse saw-tooth voltage wave appears across a condenser 35 which is charged through a resistance 36 from a source of potential of volts. The' negative voltage peaks 34 appear across a resistance 31, and are added to the sawtooth component across the condenser 35 to develop on the grid of a tube 38 a voltage wave designated by the reference numeral 39. This voltage wave is amplified by the tube 38 and is of the proper shape to develop in the plate circuit of the tube a saw-tooth current wave 43 which is caused to pass through the coils IT.

The vertical deflection circuit operates in the same manner as the horizontal deflection circuit, and the various parts making up the former have been designated by the same reference numerals, with the suffix a, as the respective and corresponding parts comprising the horizontal deflection circuit.

In the vertical deflection circuit, the grid circuit of the tube 32a is electrostatically coupled,

by a condenser ll, to the grid circuit the tube an. In this circuit, the output circuit is coupled by a resistance 42 to the vertical deflecting coils ll, whereas the output circuit of the horizontal deflection circuit is inductively coupled, by a suitable choke coil 43, to the horizontal deflecting coils ll.

Furthermore, in the vertical deflection circuit, the bias on the tube Ila is supplied by the rectii'ying action of its grid circuit building up a negative charge on the condenser ll, whereas in the horizontal deflecting circuit the bias on the grid circuit of the corresponding tube 32 is supplied by a potentiometer 44 connected across the negative voltage supply.

In describing the manner or operation of the embodiment of our invention disclosed in Fig. 1, it has been assumed, for example, that the picture signals and the synchronizing impulses are being transmitted in the same manner and by a transmitting system 01' the general character disclosed in the copending application by Ray D. Kell, flied September 30, 1931, hearing Serial No. 565,953, and assigned to the Radio Corporation of America. In such a system, the picture signals and the synchronizing impulses are transmitted in the same channel, withthe impulses at a substantially greater amplitude than the picture signals. Both the horizontal and vertical impulses are transmitted at the same amplitude,

ance is. The tubeydt is biased so that it passes only the synchronizing impulses of substantially greater amplitude than the picture signals. In the plate circuit of the tube se, the horizontal and vertical impulses are distinguished from each other by reason of their difference in steepness of wave front. For this purpose, a suitable filter circuit ll is connected in the plate circuit of the tube 53%, and supplies only the vertical or framing impulse Lib, of relatively low steepness oi wave front,

to the grid circuit of the tube 26c by way of a connection 49. The-horizontal impulses 28, of relatively high steepness of wave front, appear in a resistance 50, and are supplied by way of a connection 5| to the grid circuit of the tube 20.

With regard to the circuits is and I so per se, the period tt3 of the impulse of plate current graphically represented in Fig. 2 is about one tenth oi. the entire operating period tts in the horizontal deflection circuit, and is about one fiftieth of the entire operating period in the vertical deflection circuit. By suitably varying the values of the resistances 2| and 24d and the condensers 22 and 22a, this ratio, or in other words, the time period ta'to ts during which no plate current flows, may be varied over a relatively wide range. For example, the time .period t: to 1.: may be made as high as one minute, or even flve minutes, as required to suit the circuit for any particular purpose. It will, therefore, be seen that our improved circuit l9 may be used for many other purposes than the synchronization of deflectioncircuits in a television system. There is a great variety of commercial control systems requiring that a single, sharply-peaked control impulse reocclu' faithiully at the beginning or ending of a definite time period. For

example, in the art of maintaining clocks in ex-,

act synchronism with observatory time, a single, sharply-peaked control impulse, reoccurring once at the same instant during minute periods, would be efl'ective for this purpose. In such case, the resistance 24 and the condenser 22, in our improved circuit l9, would be adjusted so that the time period t to ts in Fig. I would be exactly one minute, and the impulses 28 would correspond to the received timing impulses under control of the master clock.

The term saw-tooth", as used in the speciflcation and claims to define specifically the graphical shape of the electrical wave in the output circuits of the horizontal and vertical deflecting circuits, is intended to mean a wave shape as used in the above copending application bearing Serial No. 544,959. That is, this particular wave shape, when'shown graphically, calls for forward deflection of the ray at a substantially constant velocity during the effective scanning action to develop picture signals, and return deflection of the ray at an average velocity which is substantially greater than the velocity during forward deflection. The saw-tooth wave form, therefore, distinguishes clearly from the wave form used heretofore in some systems wherein the velocity of return deflection of the ray is substantially constant and equal to the velocity of forward deflection of the ray. With regard to the velocity of return deflection of the ray in my improved system, it has been found that this is not constant, but is at a very high value at the beginning of the return deflection, and then diminishes perceptibly in value as the action of return deflection of the ray is completed. The sawtooth wave form referred to herein can, therefore, be said to call for the conditions wherein there is forward deflection of the ray at substantially constant velocity, and return deflection of the ray at a varying velocity which, however, averages to a value many times that of the velocity of forward deflection.

In Fig. l, the various values of resistance, capacity and inductance which have been designated have been found to provide for satisfactory operating action. However, these values are not critical in any strict sense of the word, and

may be varied over a substantial range. Furthermore, in this connection, various other changes might be made such as in the circuit arrangement, without departing from the spirit of our invention or the scope of the claims.

We claim as our invention:

1. An oscillator comprising an electron tube having grid and plate circuits, said grid circuit being excited from said plate circuit in such manner that as the plate current increases the bias on the grid of said tube increases in the positive sense and as the plate current decreases such bias increases in the negative sense, a condenser connected in said grid circuit for applying to the grid :3. potential more negative than that required for cut-off, and a resistance connected in said grid circuit and providing a discharge path for charges stored by said condenser, said electrical circuit being characterized by the fact that the respective values of said condenser and said resistance and the constants and relation of the component parts are such that a charge is stored by said condenser only once during each complete operating period and during v a relatively small part of such period and which is eflective to bias said grid'substantially below the cut-oi! point.

2., The method of developing a single sharplypeaked voltage wave periodically which comprises causing an oscillatory circuit hicluding an electric discharge tube to oscillate once during each cycle of operation, storing an electrical charge during the period of'oscillation, utilizing said charge at the end of said period to block said tube against i'urther oscillation during the entire remaining period of the cycle, and gradually discharging said charge during .said remaining period to substantially a point whereat said circuit is again free to oscillate.

, 3. The method of producinga single sharplypeaked voltage wave periodically which comprises causing an oscillatory circuit to oscillate once during each wave cycle of operation to develop only one of sai'd'voltage'peaks, storing an electrical charge during the period of oscillation, utilizing said charge at the end of said period to block said circuit'against further oscillation during the entire remaining period of the wave cycle, gradually discharging said charge -'during said remaining period'to a point somewhat removed trom that at which said circuit is again free to oscillate, and utilizing a received synchronizing impulse to complete the discharge of said charge vto a point at which said circuit is again free to oscillate.

4. An oscillator circuit for producing a sawtooth electrical wave at a given frequency, said circuit including means for limiting the number of oscillations of said circuit during'each sawtooth cycle'to -one, said means comprising a condenser for storing an electrical charge during the oscillation period and a resistance providing a discharge path for said charge during the remaining period of the saw-tooth cycle.

5. In an electrical circuit for developing a sawtooth electrical wave at a given frequency, an electron tube forming part of said circuit and having inductively-coupled plate and grid circuits, the connections being such that as the plate current increases the bias on the grid of said tube increases in the positive sense and as the plate current decreases such bias increases in the negative sense, a condenser connected in said grid circuit for applying to the grid a potential more negative than that required for cutoil', a resistance connected in said grid circuit and providing a discharge path for charges stored by said condenser, and a circuit connected to said grid circuit for supplying control signals thereto, said electrical circuit being characterized by the fact that the respective values of said condenser and said resistance and the constants and relation of the component parts are such that said tube draws plate current only once during the production of each saw-tooth wave and for a' relatively small part of the period of each of said waves, and being further characterized by the fact that during the time said tube draws plate current a charge is stored by said condenser suilicient to apply said potential to said grid for cut-oil.

6. An oscillatory circuit embodying an electron tube and having a definite period of operation; the grid circuit of said tube being excited from the plate circuit thereof, a condenser connected in said grid circuit for applying to the grid a potential more negative than that required for cutofl, a resistance connected in said grid circuit and providing a discharge path for charges stored by said condenser, a source of electrical impulses, and a connection for applying said impulses to said grid circuit, said oscillatory circuit being characterized by the fact that the respective values of said condenser and said resistance and the constants and relation of. the component parts are such that a single current impulse is developed in said plate circuit only once during each complete operating period and for a period of time a relatively small as compared to'the complete operating period.

'7. Themethod of producing a recurrent electrical wave which comprises causing an oscillatory circuit to oscillate once during each cycle of said wave to develop only one sharply-peaked voltage impulse of a given amplitude, storing an electrical charge during the period 01' development oi the voltage impulse, utilizing said charge at the end of said period to block said circuit against oscillation, gradually discharging said charge to a point somewhat removed from that at which said circuit is again free to oscillate, and utilizing a received synchronizing impulse to initiate the next succeeding operating cycle of said circuit. v

8. An oscillation generating systemconstituted by a thermionic tube having an input circuit including one winding of a transformer, a grid-condenser and a grid-leak, and an output circuit for the tube including another winding of the transformer, the system being characterized by the fact that the constants of the several components enumerated are such that the grid of the tube, when 1 oscillations are being generated, draws sufiicient current during a single half-cycle to reduce its potential far below the cut-off point, and being further characterized in that the time constant of the grid-condenser and grid-leak is such as to maintain the grid potential below the cut-ofl point for a length of time, between successive oscillations, greatly in excess of the time required for a complete oscillation cycle. 1 9. The invention set forth in claim 5 still further characterized in that the losses in the grid circuit are so high as to substantially preclude free oscillations therein at the natural period of the system.

10. An oscillator for producing electrical impulses periodically, said oscillator comprising an electron discharge tube having a control grid and having a plate circuit and a grid circuit, said circuits being inductively coupled by means of a transformer having a primary winding in said plate circuit and a secondary winding in said grid circuit, said coupling being in such direction that said control electrode is made more positive in response to an increase in plate current, a grid condenser connected in series with said secondary winding whereby said condenser receives a charge of the proper polarity and of suflicient magnitude to block said tube, and a grid resistor for causing said charge to leak oil, the values of said grid condenser and said grid resistor being so high and the damping of said plate and grid circuits being so great that each cycle of operation of the oscillator includes a damped sine wave followed by a period of rest, said damping being so great that said grid is driven positive only once during the occurrence of said damped wave. a

11. The invention according to claim 10 characterized in that the product of said grid condenser capacity and said grid resistor resistance is such that said period of rest is at least as great as the period of occurrence of said damped wave.

12. The invention according to claim 10 characterized in that the product of said grid condenser capacity and said grid resistor resistance is such that said period of rest is substantially greater than the period of occurrence of said damped wave.

13. An oscillator for producing electrical impulses periodically, said oscillator comprising an electron discharge tube having a control grid and having a plate circuit and a grid circuit, means for inductively coupling said circuits in such direction as to make said grid more positive with increase of plate current, said circuits being highly damped whereby they can oscillate to produce a damped sine wave only, and a grid condenser so connected in said input circuit that once during each cycle of operation it receives a charge which makes said grid negative, said charge being of sufficient magnitude to block said tube, and a grid resistor for causing a substantial portion of said charge to leak on gradually during said cycle, the values of said grid condenser and said grid resistor being such that said cycle includes a damped sine wave followed by a period of rest during which said charge is leaking off, and the damping of said circuits being so great that said grid is driven positive only once during the occurrence of said damped sine wave.

14. An oscillator for producing electrical impulses periodically, said oscillator comprising a vacuum tube having a cathode, a control grid and a plate, a transformer having a primary winding and a secondary winding, means for applying a positive potential to said plate, said primary winding being connected between said cathode and said plate, a condenser connected in series with said secondary winding, said condenser and secondary winding being connected between said cathode and said grid, the coupling through said windings being in such direction that said grid/is made more positive in response to an increase in plate current, and a grid leak resistor connected in shunt to said condenser, said condenser and said grid resistor having such values and the damping of said plate and grid circuits being such that the oscillator repeats a cycle of operation, each cycle consisting of a damped sine wave and a period of rest.

15. The invention according to claim 14 characterized in that the product of the capacity of said condenser and the resistance of said resistor is such that said period of rest is at least as great as the period during which said damped sine wave occurs.

16. An electrical circuit for generation of electrical impulses comprising an electron tube having a cathode, a control grid and a plate, an inductance coil in its plate-cathode circuit and another inductance coil in its grid-cathode circuit, said coils being inductively coupled to each other and having a certain capacity across at least one of the inductance coils, and a condenser by-passed by a resistance and in series with the grid inductance coil, the values of the several circuit elements being such that one complete cycle of operation includes one damped sine wave determined in frequency by the value of the product of said certain capacity and the inductance thereacross which is followed by a period of rest determined by the product of the by-pass resistance and the capacity of said condenser, said rest period having been caused by the charge accumulated during the period of flow of grid current through the grid coil, said charge being of sufiiciently high value to shut off the plate and grid currents in the tube until such time that the gradual leak of the said charge through said resistance so reduces the said charge and so lowers the bias of the control grid that the plate current may begin to flow again and the damped sine wave part of the cycle may start over.

17. An oscillator for producing electrical impulses periodically, said oscillator comprising an electron discharge tube having a control grid and having a plate circuit and a grid circuit, said circuits being inductively coupled by means of a transformer having a primary winding in said plate circuit and a secondary winding in said grid circuit, said coupling being in such direction that said control electrode is made more positive in response to an increase in plate current, a grid condenser connected in series with said secondary winding whereby said condenser receives a charge of the proper polarity and of sufiicient magnitude to block said tube, and a grid resistor for causing said charge to leak off, the values of said grid condenser and said grid resistor being so high and the damping of said plate and grid circuits being so great that each cycle of operation of the oscillator includes a damped sine wave followed by a period of rest, said damping being so great that said grid is driven positive only once during the occurrence of said damped wave, and means for impressing synchronizing impulses of positive polarity upon said control grid.

18. An oscillator for producing electrical impulses periodically, said oscillator comprising an electron discharge tube having a control grid and having a plate circuit and a grid circuit, means for inductively coupling said circuits in such direction as to make said grid more positive with increase of plate current, said circuits being highly damped whereby they can oscillate to produce -a damped sine wave only, and a grid condenser so connected in said input circuit that once during each cycle of operation it receives a charge which makes said grid negative, said charge being of suflicient magnitude to block said tube, and a grid resistor for causing a substantial portion of said charge to leak off gradually during said cycle, the values of said grid condenser and said grid resistor being such that said cycle includes a damped sine wave followed by a period of rest during which said charge is leaking off, and the damping of said circuits being so great that said grid is driven positive only once during the occurrence of said damped sine wave, and means for impressing a positive synchronizing impulse upon said grid during said period of rest.

1 WILLIAM A. TOLSON.

JUSTIN R. DUNCAN.

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