US2251851A - Electron-beam deflecting circuit - Google Patents

Description

Aug. 5, 1941. R, CQMOORE 2,251,853;

ELEcTRoN-BEAM DEFLEGTING CIRCUIT.

Filed June 16, 1939 3 Sheets-.Sheet 'l fipa,

Aug. 5, 1941. R. c. MOORE ELECTRON-BEAM DEFLEGTING CIRCUIT Filed June 16, 1939 3 Sheets-Sheet 2 Aug. 5, 1941.

R. c. MOORE 2,251,851

ELECTRON-BEAM DEFLECTING CIRCUIT Filed June 16, 1959 3 Sheets-Sheet 3 Patented Aug. 5, 1941 ELECTRON-BEAM DEFLECTING CIRCUIT Robert C. Moore, Philadelphia, Pa., assigner, by

mesne assignments, to Philco Radio and Television Corporation, Philadelphia; Pa., a corporation of Delaware Application June 16, 1939, Serial No. 279,581v

16 Claims. (Cl. Z50-27) tion of each scan to return it toits value at the This invention relates to electron-beam deflecting circuits of the type employed in electronic television systems both at the transmitter where the television signal is generated by the scanning loi a charge image corresponding to the scene to be televised and at the receiver where the scene is reconstituted by the scanning of a uorescent screen by a beam of electrons modulated in accordance with variations in the received signal. More particularly, the invention relates to that method of deecting the beam which employs a varying magnetic eld that builds up slowly at a uniform rate and decays suddenly, or vice versa.

As is well known, the scanning process at the television receiver must be carried out in substantially the same manner as that at the transmitter in order that an accurate reproduction of the televised picture may be obtained. With this in view, it has become common practice to reduce the scanning process to a routine which may readily be duplicated at the receiver to conform with that carried out at the transmitter. The routine which has been generally adopted is one in which the beam is deilected so that the -point at which it impinges upon the surface being scanned traces a series of vertically spaced substantially horizontal lines. Furthermore, the angular rate at which the scanning beam is deected both horizontally and vertically should be substnatially uniform though the rate itself will be different in the two cases. Such uniform deflection is obtained by permitting the electrons in the beam to traverse a region in which either an electric or a magnetic lield is caused to build up or to decay at a uniform rate A uniformly varying electric eld may be obtained by impressing a sawtooth voltage upon the plates of a condenser While a uniformly varying magnetic eld may be obtained by establishing in a coil a current having a sawtooth waveform. Although electric deection is generally more conservative of energy under practical conditions than magnetic, unusually high voltages are required to obtain sufficient deflection so that it is not generally used where large deflections are required.

Two considerations are of primary importance in the design 4of a magnetic deflecting system.

One involves the production in the deecting coil I of a uniformly varying current in spite of the ,presence of fortuitous circuit elements and other rapidly in the opposite senses upon. the complebeginning thereof. A second consideration is that of power consumption which should be kept as low as possible, although it is inherently higher in a magnetic than in an electric deilecting system. f

Accordingly, one object of the invention is to provide a high eilciency magnetic deflection system for use in television.

Another object of the invention is to provide a magnetic deflection system for deilecting an electron beam at a substantially uniform rate through a given angle and for suddenly returning it to its initial position.

Still another object of the invention is to provide a magnetic deflecting system of the type adapted to be actuated by a signal supplied to its input in which the fundamental scanning frequency i's dependent upon the input signal' characteristics but in which the rate of deection throughout the scan is substantially independent of the input signal.

A further object oi. the invention is to provide automatic means responsive to the output signal in a. defiecting system for controlling the amount of energy supplied to its input whereby the desired waveform obtains in the output of the system.

A still further object of the invention is to provide a means for producing a substantially linear sawtooth current in the deecting coil of a magnetic deilecting system.

The invention will be understood clearly from the following description and drawings in which:

Figs. 1, 2, and 3 are diagrammatic illustrations of different embodiments of the invention; and

Fig. 4 shows a series of voltage and current waveforms, existing in various parts of the systems to be described.

By way of introduction and before considering the methods and apparatus of the invention, it will be desirable to describe in some detail the operation of a conventional deecting output system of the magnetic type. Such a system is the one of Fig. 1 omitting for the moment the resistors il and i3, the condenser l2 and the associated connection represented by the heavy line, which comprise (additions to the fundamental circuit made in accordance with the principles ofthe present invention. The nucleus of the circuit is an inductance l in which is it desired to set up the sawtooth deilecting current. This inductance may either be the delecting coil itself or, as in the case illustrated, may be a separate inductor forming the primary of a duration of the steeper portion of the sawtooth is dependent upon the magnitude of this fortuitous capacity which should, therefore, be as small as possible.

In order to set up a sawtooth currentdn the inductance I, it is necessary to impress thereacross a signal comprising abrupt peaks or impulses. The inductance is accordingly included in the output circuit of a suitable space discharge device 6 to the input electrode of which is supplied an impulse voltage of the form shown at 1. Although a system such as described thus far may be used, it is wasteful of power since energy must be supplied to the inductance throughout the entire scan. Improved efficiency is frequently obtained by connecting in shunt with the inductance I a diode 8 which may be suitably biased by means oi the time circuit comprising the resistor 9 and the condenser I 0, or by other suitable means, so as to limit the amplitude of the voltage developed across the inductance.

It will be remembered that the resistor II is to be omitted for purposes of the present consideration. By the provision of the diode and biasing means, a sort of class B operation is obtained in which energy is supplied to the inductance I by the tube 6 during only the latter portion of each scanning period. When the tube is cut off at the end of the line by a large negative pulse applied to its grid, the energy in the inductance I is rapidly transferred to the capacity 5, the upper plate of which assumes a positive charge with respect to ground. When the charge on the condenser has reached a maximum and the current in the inductance has fallen to zero, the free oscillationcontinueswiththe discharge of the condenser to produce a current in the opposite direction in the inductance. This continues until the condenser has been discharged and the current in the inductance has become a maximum in the opposite direction. Were it not for the presence of the diode 8 or equivalent means, the capacity 5 would now proceed to charge in the opposite sense, since its upper plate becomes negative with respect to the lower. developed is such as to cause the diode 8 to conduct, and the current in the inductance, instead of charging the condenser, flows through the return path provided by the diode 8. By reason of the resistance of the diode and its associated biasing means, the current decreases exponentially until all, or substantially all, of the energy stored in the inductive field has been dissipated,

when the tube 6 is caused to supply energy thereto and the current increases.

Although the diode when properly biased serves to control the decrease of the current in the inductance, thereby utilizing the energy supplied tothe inductive field during the latter half of each scanning line to control its operation during the rst half of the succeeding line, its operation is not entirely satisfactory since the current in the series circuit, comprising the diode, its biasing means and the inductance, tends to decrease substantially exponentially thereby producing a distorted sawtooth, Such as However, the voltage thus that indicated by the solid line curve at D in Fig. 4. This should be compared to the desired sawtooth wave iorm shown at A in Fig. 4, which requires that the voltage on the plate of the tube E vary as shown at B in Fig. 4.

It follows that the voltage across the inductance must be the vector difference between the plate supply voltage and the voltage on the plate of the tube itself, which is approximated by the wave represented by the solid line at C. In the absence of the diode, the oscillation which takes place in the circuit comprising the inductance I and the capacity 5 during the time the tube 5 is cut od. would tend to overshoot the level portion of the solid line curve as indicated by the broken line curve. By using the biased diode or its equivalent, this tendency to overswing at the end of the return time is avoided. The net result is a current in the inductance which is substantially as shown by the solid line curve at D in Fig. 4. If the deiiection is to be linear, this must be modified so as to conform with the dotted lines in the same figure. j

Considering now the diode current when the system is operating as described above, it will be found to vary substantially as represented by the curve E of Fig. 4. In order to obtain the desired linear sawtooth current in .the inductance I, this should be modified to conform with thatrepresented by the solid line curve F of Fig. 4, or additional means should be provided so that the total current in the inductance during the first half of each scanning line varies in this manner. This might be accomplished by varying the series resistance of the circuit comprising the diode, its biasing means, and the inductance, so as to obtain the desired current waveform. This woulid obtain if the series resistance were to be increased linearly duringthe first half of each scanning line.

In accordance with the present invention, however, it is proposed to permit the driver or output tube 6 to draw current in an amount suiiicient to supply the'difference between the diode current and that desired in the inductance. Ac-

cordingly, the series resistance of the diode circuit might be adjusted so that the initial slope of the corresponding curve of current decay .therein will be equal to the desired slope of the sawtooth current, as indicated by the dotted curves at I" in Fig. 4. The driver tube may then be controlled so as to supply the required complementary current during the rs't half of the scanning cycle and so as to increase in substantially linear fashion during the latter half of the cycle. 'I'he desired wave of currentl in the tube 6 may accordingly be of the form shown at G in Fig. 4. Although the current in the tube 6 may be thus controlled by the application of a suitable control signal to the grid of tube 6 from some external source, it has been found that the desired control may be obtained from the output circuit itself. This method is particularly advantageoussin'ce it makes the output self-regulatory and independent of any of the idiosyncrasies of the usual deiiecting signal generators, which are attributable to failure to synchronize as well as to properties of the. circuits themselves. The present method obviates these difficulties so that the Waveform of the deiiecting coil current is automatically self-controlled, only the beginning and end points of each scanning line being dependent upon the externally supplied synchronizing signal.

In the embodiment of Fig. 1, a control voltage current in the inductance may be controlled by may be derived across a resistor II included in the diode circuit. This is fed back to the input circuit of the tube 8 by the heavy-line connection which includes the blocking condenser I2. The resistor Il must necessarily be relatively small in order not to interfere wtih the normal and de-,`-

sired operation ot the diode B, and hence in order not disadvantageously to increase the load upon the signal source, it may be necessary to introduce the resistor I3 in the connection. The magnitude oi this will, of course, be chosen with a view to the effective internal impedance of the source applying signal to the tube 6. Nowfit will be noted that early in the scanning period, when the diode current is large, an appreciable negative voltage will develop across the resistor Il. This will tend to cut oif the tube 8. As the current in the diode circuit decays, the resistor voltage decreases thereby decreasing the bias on the tube 6 which, if the fixed bias provided by the combination of the resistor il and the condenser i5 is of a suitable value. may be caused to draw the required complementary current to give a current wave-form as shown at I6 in the inductance i. The bias developed acrossthe resistor ii may vary as indicated at i'I throughout the scan, from which it appears that no control would be exercised during the latter part of the scan, and this may indeed be the case provided that the input signal "i is substantially constant throughout. However, if this is not the case and the input signal swings excessively positive at any time, the voltage developed across the inductance i by the more than linear increase in current therethrough will cause the cathode of the diode to swing more negative with respect to its plate. Consequently, diode current will ow and the bias thereby developed, when supplied to the grid of the tube t will compensate for the variation in the input signal and will restore equilibrium in the output. This' restoring force, it should be noted, will be developed Whenever during the scanning period-the current in the inductance (l tends to increase at too great a rate, and adequately compensates for any changes in the input signal. In general then, the only characteristic which this signal must possess is a relatively well defined negative peak sufficient to insure cut off of the tube ti throughout the entire return time. The end of each scanning cycle and the beginning of the next cycle will depend upon the time of occurrence oi these peaks, but otherwise the operation of the circuit Will be substantially independent of the form of the input signal. This will, of course, permit the obtaining of the de sired uniform deflection of an electron beam in a television picture tube or like device.

It has been observed that it is not feasible to make the resistor ii unduly large, which may place a limitation upon the available bias for controlling the tube One Way of obviating this diiiculty is by the use of an additional diode, as shown in the embodiment ofFig. 2. Here the diode t carries the major part of the current from the inductance i and has no resistance in series with it, other than that of the biasing means. The bias voltage is derived across a relatively larger resistor ii than the one used in the previous embodiment,l which is connected in series with the additional diode i8. This avoids any loading diiilculties which might otherwise obtain, while giving the desired control in substantially the same manner as-heretofore described.

As has already been noted, the ldecay of the varying theI resistance in the diode circuit in a suitable manner. This may be effected, as shown in Fig. 3, by substituting for the diode an inverted triode or a tetrode I9. In order to obtain the desired sawtooth current, the resistance should be increased uniformly which 'may be accomplished by applying a sawtnoth voltage to the'controi grid of the tube I9. Since impulse voltage is available on the plate of the tube 6, a sawtooth voltage may be obtained by applying the impulse voltage across a series combination comprising a resistor 20 and a condenser 2 I. The condenser voltage will then correspond to the solid'curve 22. The voltage drop across the resistor 20 will -accordingly be the difference between the voltage on the plate of the tube 6 and that across the condenser which, measured with respect to the plate of the tube, corresponds to the dotted curve 23. This is such as to give the desired resistance variation when applied to the grid of the tube I9.

This mode of controlling the current in the inductance'i should, of course, give the desired waveform therein provided that the proper signal is applied to the input of the tube il. However, sinceI it is desirable that the current in the coil i should be independent of the input signal to as great a degree as is possible, the method of the invention may be advantageously employed in this case also. Accordingly, the resistor ii is provided in the plate circuit of the tube iii, i'rom which bias voltage may be derived and fed back through the condenser 2li which by-passes the D. C. plate voltage dropping resistor 25. In this case, the control is applied to the screen grid of the tube t. It will, of course, be understood that the bias voltage may be aplplied in any suitable manner to controlthe driver tube. In the case where the source of external signal to be applied to the grid of the tube is a gas discharge tube oscillator or similar device Whosel operation is deleteriously affected by the variation in plate voltage which the bias may produce, it is desirable to apply the bias in some way which will not so affect it. One such method is by applying the bias to the screen grid, as here shown. Another method is to apply the bias across a resistor in the cathode circuit of the gas tube oscillator whereby the entire oscillator circuit fioats up and down on the bias voltage but there is no appreciable effect upon its synchronizatori.

From the above explanation of the principles of the invention it will be clear to those skilled in the art that there are numerous extensions of the principles within the scope of the invention. Thus the invention should not be regarded as limited to the specific embodiments shown but is rather defined by the scope of the appended claims.

I claim:

l. In an electron beam deiiecting system wherein a magnetic field is varied to deect electrons passing therethrough; means responsive to elecy trical energy supplied thereto from an external source for establishing a varying magnetic field; means coupled to said last means for removing energy'from said field, when the strength of said eld reaches a maximum in a particular sense, for storing said energy and for returning it to said field so as to build up said field in the oppo-l site sense; means for controllably dis'sipating the energy contained in said field when it is of said opposite sense; and means for controlling the amount and sense of the energy supplied to said field from said external source in accordance with the rate at which said energy is controllably dissipated.

2. In an electron beam deilecting system, in ductive means adapted to set up a varying magnetic field in response to a current produced therein; controllable means for altering the current in said inductive means; means adapted to store the energy contained in said magnetic ieid and to effect a reversal of the current in said inductive means when the said current has ceased to be changed by the operation of said second means; means connected in shunt with said inductive means and adapted to conduct whenever the current therethrough` tends to increase at greater than a predetermined rate; and means responsive to the current in said last means for controlling the current alteration in said inductive means by said second means in accordance with the current in said last means.

3. In an electron beam deflecting device employing magnetic deflecting means; a resonant circuit comprising the inductance and distributed capacitance of said magnetic deiiecting means; controllable means for supplying energy to and removing energy from said resonant circuit; a diode and a serially connected biasing means connected across said resonant circuit; and means responsive to the current in said diode for controlling the energy transfer between said energy supply means and said resonant circuit.

4. In an electron beam defiecting device employing magnetic deecting means; a resonant circuit including the inductance of said deflecting means; a source of a signal adapted to excite said resonant circuit; means for supplying said signal to said resonant circuit; means connected in shunt with said resonant circuit and adapted to conduct whenever the voltage across the said resonant circuit exceeds a predetermined value; means for deriving a signal proportional to the current in said last mentioned means; and means for applying said derived signal so as to modify the signal supplied to said resonant circuit from said source.

5. In an electron beam deecting system; means supplied with electrical energy for establishing1 a periodically varying electromagnetic eld in a region traversed by the electrons of said beam; controllable means adapted to supply energy to said iirst means during a part of each cycle and capable of dissipating energy therefrom during a different part oi? the cycle; means coupled to said rst means and adapted to remove energy therefrom and to store it during a part of the cycle and to return said energy thereto during another part of the cycle; means connected to said rst means for dissipating energy therefrom during a part of the cycle; and means for controlling the amount of energy supplied or dissipated by said second means in accordance with the rate of which energy is dissipated by said last-named means.

6. In an electron beam deflecting device employing magnetic deilecting means; a resonant circuit comprising the inductance and distributed capacitance of said magnetic deiiecting means; controllable means for supplying energy to and removing energy from said resonant circuit; a serially connected diode, impedance, and biasing means connected in shunt with said resonant circuit; and means for applying the vvolt-- age developed across said impedance to control the energy transfer between said energy supply means and said resonant circuit. '1

'7. In an electron beam deilecting device employing magnetic deiiecting means; a resonant circuit comprising the inductance and distributed capacitance of said magnetic deecting means; controllable means for supplying energy to and removing energy from said resonant circuit; a diode and a serially connected biasing means connected in shunt with said resonant circuit; a second diode and a serially connected impedance also connected in shunt'with said resonant circuit; and means for applying the voltage developed across said impedance to control the energy transfer between said energy supply means and said resonant circuit.

8. In a electron beam deflecting system; in-

ductive means adapted to set up a varying magnetic field in response to a current produced therein; controllable means for altering the current in said inductive means; means adapted to store the energy contained in said magnetic field and to eiiect a reversal of the current in said inductive means when the said current has ceased to be changed by the operation of said second means; a space discharge device having a Work circuit and a control circuit, and having its work circuit coupled to said inductive means; means for controlling the current in said work circuit so as to cause the current in said inductive means to decrease at a substantially uniform rate; and means responsive to the current in said work circuit for controlling the alteration in the current in said inductive means by the said second means.

9. In an electron beam deecting system, inductive means adapted to set up a varying magnetic field in response to a current produced therein, a circuit including a space discharge device connected to said inductive means, control means including another space discharge device connected to said circuit, a source of control signals connected to said other space discharge device, means for deriving a control voltage from said circuit, and means for applying said control voltage to said other space discharge device to controllably bias the same.

l0. In an electron beam deflecting system, inductive means adapted to set up a varying magnetic field in response to a current produced therein, a circuit connected to said inductive means, said circuit including serially a space discharge device, biasing means therefor, and an impedance, control means including another space discharge device connected to said circuit, a source of control signals connected to said other space disharge device, means for deriving a control voltage from said impedance, and means for applying said control voltage to said other space discharge device to controllably bias the same.

l1. In an electron beam deflecting system, inductive means adapted to set up a varying magnetic eld in response to a current produced therein, a non-linear device in shunt with said inductive means for controlling the current therein, signal responsive means including a space discharge device connected to said inductive means and said shunt means, a source of control signals connected to said space discharge device, means for deriving a control voltage from the current in said non-linear device, and means for applying said control voltage .to said space discharge device to controllably bias the same.

l2. In an electron beam deiiecting system, an electron discharge device having at least a control grid, a cathode and an anode, a source of signals connected to the grid-cathode circuit of said device, an inductance connected to the anode-cathode circuit of said device for producing a varyingl magnetic iield in response to said signals, a non-linear device in shunt with said inductance for controlling the current therein, means for deriving a control voltage from the current in said non-linear' device, and means for 'applying said control voltage to said electron discharge device to controllably bias the same.

13. In an electron beam deilecting system; a series circuit comprising a. source of electrical energy, inductive means adapted to set up a varying magnetic eld in response to a current produced therein, and controllable impedance means for regulating the ilow of current in said series circuit; a source of a control signal; means for applying said signal to said impedance to control the same; space discharge means shunting said inductive means; means for deriving a control voltage dependent upon the current in said space discharge means; and means i'or applying said voltage to said impedance means to further control the. same.

14. In an electron beam deilecting system; a series circuit comprising a source of electrical energy, inductive means adapted to set up a varying/magnetic iield in response to a current produced therein, and controllable impedance means i'or regulating the flow of current in said series circuit; a source of control signal; means for applying said signal to said impedance to control the same; a second controllable impedance means shunting said inductive means; means for controlling the impedance of said second impedance means in response to the voltagedeveloped across l said inductive means; means for deriving a control voltage dependent upon the current in said second controllable impedance means; and means for applying said voltage to said first impedance means to further control the same.

15. In an electron beam defiecting system; a space discharge device having at least an anode, a cathode, and a control grid; an inductance connected in the anode circuit of said space discharge device; a circuit comprising a serially connected diode and an impedance element connected in shunt with said inductance; a connection from the junction of said diode and said impedance element to the grid of said space discharge device; and a source of a controlling signal connected to the grid of said space discharge device.

16. In an electron beam deilecting system; a space discharge device having at least an anode, a cathode, and a plurality of controlling electrodes interposed between said cahtode and said anode; an inductance connected in the anode circuit of said space discharge device; a circuit connected in shunt with said inductance, said circuit including a triode space discharge device and an impedance element; a connection from the junction of said triode space discharge device and said impedance element to one of said. controlling electrodes; and a source of a controlling signal connected to the one of said controlling electrodes.

ROBERT C. MOORE.

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