US2418425A - Self-synchronized saw-tooth generator - Google Patents

Description

pr l, 1947. I W. 1 POCH 2,418,425

sELF-sYNcHRoNIAzED SAW-TOOTH GENERATOR Filed Jan. 27, 1943 I EFLECNG mhwrefloc `TTOIPIVEK Patented Apr. 1, 1947 SELF- SYNCHRONIZED SAW-TOOTH GENERATOR Waldemar J. Poch, Morristown, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application January 27, 1943, Serial No. 473,666

(Cl. Z50-36) 2 Claims.

This invention relates to television or oscillographic apparatus, and is particularly concerned with the circuits thereof serving to supply energy to the deecting coils or plates of a cathode ray tube to deflect the electron beam therein developed across an impacted target area.

Broadly speaking, the invention is concerned primarily with television receiving or transmitting apparatus wherein a cathode ray tube is used either as an image scanning or an image reproducing tube, although the invention also finds application tothe usual oscillograph type of apparatus wherein a transient or other phenomena produced on the viewing target by a cathode ray tube is caused to appear at predetermined'repetition rates.

In its essence, the invention herein to be disclosed includes the use of a triggering and discharge tube in co-operative relationship with respect to an energy storing element and arranged to co-operate with a suitable output tube which delivers energy to the electron beam delecting system.

In combination with this arrangement, provision is made for feedingback a portion of the energy from the output tube to the discharge tube to control its operation. Provision is also made fOr exercising an external control over the rate at which the discharge .tube is controlled by the energy feedback from the output tube by means of a synchronizing impulse serving as an auxiliary control to lock definitely the operational cycle to some desired value.

In its essence, the invention herein provided is for the purpose of simplifying previously known circuits and, at the same time, avoiding the use of the frequently used so-called blocking oscillator tube normally used to develop energy pulses to control the discharge action of the discharge tube whereby the desired form of sawtooth wave energy is developed.

A still further object of this 'invention is that of providing a circuit and system which operates efficiently and yet avoids the necessity of heretofore used oscillator tubes incorporating both tube elements, transformers and the like, so that the present invention not only makes provision for reducing the number of tubes heretofore used and required for deflection purpose-s, but also is of a nature such that the weight of the component parts of the system is reduced by virtue of the complete omission of heretofore used transformers embodying heavy iron cores or the like.

Other objects and advantages of the invention are those of providing simplifications in circuit arrangements which overcome known defects of prior art systems and which, at the same time, serve to provide improved operation of the ycomplete system.

Other objects and advantages will become apparent from reading the following specification and claims in connection with the accompanying drawing, wherein one form of circuit capable of accomplishing the aims and objects of the invention has been set forth by way of diagrammatic illustration.

Referring now to the drawing, the herein described deflecting circuit comprises essentially two independent tube elements II and I3, in which the tube I I serves as the so-called discharge tube and the tube i3 serves as the socalled output tube which is to deliver the energy to the electron beam deecting system. l

In the arrangement disclosed, the discharge tube II comprises essentially an envelope including a cathode I5, a control electrode I'I and an anode or plate electrode I9, with the cathode I5 preferably connected to ground 2I in its normal form of operation, although it is apparent that the connection may be made to any other point of substantially iixed potential.

Connected between the output or anode element I9 and ground 2| is a storage condenser 23 which is adapted to be charged from a source of energy (not shown) but connected to the terminal 25, marked +B (thus representing also a source of plate potential) which charges the condenser 23, preferably through the high resistor 21, so that when the condenser is periodically discharged by conduction within the discharge tube I I, a sawtooth voltage wave, such as that represented at (a), will be produced at the point 29, and represents the potential of the upper plate of the condenser 23 relative to ground 2l, for instance. In normal operation, the sawtooth voltage wave (a) appearing at the point 29 is then fed by way of the coupling condenser 3l to the control electrode 33 of the output tube I3, which includes also the cathode 35, the screen electrode 3l and the plate or anode output electrode 39,

with the cathode element 35 preferably biased terminal winding 45 of an outputtransforiner 41.

The secondary winding 49 of the output transdetermined largely in accordance with the fre? quency of the deflecting energy applied to the deflecting coils,

It will be noted that the screen electrode 3l is also shown as deriving its potential relative to ground 2| by virtue of the connection of the source of energy at the terminal 43. I-Iigh frequency energy is by-passed to ground 2l from the source connected to the terminal 43 by way of the condenser 53. Thus, voltage for both the screen electrode 3l and the'plate or anode electrode 39 is supplied from the terminal ?,A and flows through the transformer primary 45.

A connection` is provided between the terminal point 5-5 at the upper end of the transformer primary l5 back to the control 'electrode I'l of the vdischarge tube II through the conductor 5I in which is provided the capacity element 59. At the same time, a leak resistor 6I is provided between the control electrode Il of the discharge tube I I and ground 2l. v

In case of electrostatic deflection of a cathode ray beam, the transformer 41 may be omitted and the energy output from tube I3 may be fed to the electrostatic deflecting plates (not shown) and a suitable form of differentiating circuit is then included in the line 51 to supply an energy pulse to control the operation of the discharge tube I I, as will hereinafter become more apparent in considering the operation of the system.

Control impulses fromA any suitable source of synchronization pulses may be applied to regulate the operation of the system from an external source by way 'of the connection provided at the terminal E3 by way of the conductor 55 to the control electrode Il. As an alternative, the synchronizing control signal may be supplied through l of the blocking oscillator type is used. Such a tube operates generally to produce oscillations by virtue of a coupling connection provided between the output and the input circuit through a transformer with the feedback energy adapted to apply a charge to a grid condenser to drive the tube grid positive. At such time, the grid potential becomes quite positive with regard to the cathode of the tube, so that the tube commences t0 draw grid current and, accordingly, a negative charge is placed on the grid condenser which then tends to block the tube or bias the cutoff; The same potentials which are active upon the control elec,-v trode of the blocking oscillator tube are applied to the control electrode or grid of the discharge tube, which would be equivalent to the tube II herein disclosed. l However, in the circuit herein set forth, it will be noted that there is no blocking oscillator tube included in the system, but, to the contrary, the synchronizing signalinput energy which is in the natureof apulse, it being assumed herein 4 that the synchronizing signals for controlling the operation of the cathode ray device have been separated from video signals which they accompany, will be applied to the input terminal 63. Let it be assumed, then, that the tube II is caused to draw current at such a time.,

Prior to the time when the tube II draws current, the condenser 23 has been charging through the resistor 2l, so that the upper plate of thel condenser charges positively relative to ground along the path indicated by the sawtooth wave form (a), but as soon as the tube II draws current, vthe charge in the condenser is discharged through the tube and a new charge is built up to form the next cycle of the sawtooth wave form.

The voltage thus appearing at thev point 29 is then transferred through the coupling condenser 3l. tov control the grid of the output tube I3 and to cause it to draw current, With the controlling voltage being of the form shown by the wavey (a) When the tube I3 draws current, its output.V energy is fed through the transformer primary d., but by virtue of the effect of the transformer winding, there is produced not only a sawtooth .i component, as represented by the wave (b), but

also an impulse component of oppositeipolarity, in this instance positive as indicated by the tipv4 portions (c) of the wave (b), as well as sawtooth component (d) herein indicated as being of neg--V atve polarity. The impulse component-(c) is then fed back to the controlV electrode I'l of the, discharge tube II through the condenser 5.9, so4 that it will serve toV trigger the tube I I and cause it to draw current to discharge the condenser 23, which has acquired a charge intermediate, the recordings of each of the impulse components (c) andl thus another sav/tooth of energy is` applied to the control electrode 33 of the outputtube.v

In the case of the transformer shown, the impulse section of the wave is available,y as well as the sawtooth section, but if only the sawtooth section were developed, it is apparent that the impulse section couldv still be made available byf feeding a part of the output of the outputs tube I3 to condenser 5S through'any desiredl type of differentiating circuit.

Whatever charge is built up in the condenser 59 by virtue of the feedback connection (both to cause tube Il to draw current and later to block it) leaks olf within the time cycle measured by the time constant of the condenser 59 and theV leak resistor 6 I, either of which elements may be varied as desired to alter the time constant.

From what has been stated, therefore, it is apparent that the operation of the tubes Il and I3, taken together, provides a purely automatic means to provide for the generation of sawtooth wavel impulses which may be transferred to the output terminals 5l to control the deecting'coils (not shown) for defiecting a cathode ray beam. The rate at which the sawtoo-th deflection takes placewill be determined, generally speaking, by the time constant introducedv through the condenser 59 and the resistor 6I. However, for the purpose of exercising an auxiliary control,'it is apparentV that the receipt of synchronizing impulses at the terminal B3 will be adequateto trigger the tube II, if the time constant of the condenser 59 and the resistor Bill is made; equal to, or just veryl slightly longer, or even j ust slightly shorter (under some conditions)` than theV time interval be: tween thevreceipt of successive impulse. synchroy nizing signal energy at. the'input terminal, 6%

Thus, the synchronizing signals, as received, serve ergy, shown by curve (a), to cause the deflection to be completely synchronous with that of the control point, but, in the absence of receipt of synchronizing signals, the circuit functions in purely automatic manner to maintain the continual deflection of the cathode ray beam which is controlled by the deflecting coils notI shown.

It is apparent, furthermore, that the charging energy to the condenser 23 may be varied by varlation of the value of the resistor 21 so as to control, for instance, either the height or the Width of the picture, in accordance with the amplitude of the deflection produced, or this control may be exercised by virtue of a second resistor placed in series with the resistor 21.

Other and further modifications may Vbe resorted to Where such modifications fall Within the spirit and scope of what is hereinafter claimed.

I claim, and desire to secure by Letters Patent, the following:

1. A sawtooth Wave generating circuit comprising an electrical storage element having one terminal thereof connected to ground, a source of energy and a substantially constant current element connected to the ungrounded terminal of said storage element normally to charge it relatively slowly in the direction of maximum charge, a first thermionic means having an anode, a cathode, and a control electrode, a direct connection from the cathode to ground and a connection from the anode to the ungrounded terminal of said storage element to reduce the charge abruptly substantially to a minimum value during conductive periods of the said thermionic means, a

second thermionic means connected to said energy storage element to produce amplified output energy of a Wave form closely approximating that of the electrical charge in said storage element, a differentiating means for developing energy pulses from the amplified output energy at time periods corresponding to the abrupt change in storage element charge, a time constant circult including a series connected capacity and a resistor element for supplying said developed energy pulses to the first thermionic means to control the operative periods thereof, said time constant period being of the same order as thatv desired in the developed saWtooth Wave, and a utilization circuit connected to respond to the output energy of the second thermionic means.

2. The wave generating circuit claimed in claim l comprising, in addition, means for supplying auxiliary control signals of predetermined frequency to said rst thermionic means whereby the frequency of the developed sawtooth substantially coincides with that of the control signals.

WALDEMAR J. POCI-I.

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

UNITED STATES PATENTS Number Name Date 2,159,493 Wright May 23, 1939 2,241,619 Sherman May 13, 1941 2,300,524 Roberts Nov. 3, 1942 2,254,031 Faudell Aug. 26, 1941

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