US2927998A - Automatic damping means in deflection circuits - Google Patents

Description

March 8, 1960 H. E. THOMAS ET AL 2,927,998

AUTOMATIC DAMPING MEANS IN DEFLECTIQN CIRCUITS Filed Feb. 25, 1955 amaze /7 PEAKED SAW mOTH SYNC. PM 55 SOURCE 1 YOKE INVENTORS HARRY E- THOMAS SYLVEJTER A. 05 MARS AGENT in series with the charging capacitor.

AUTOMATIC DAMPING MEANS IN" DEFLECTION cnzcurrs Harry E. Thomas, Montclair, and Sylvester A. DeMars, Ridgewood, N.J., assignors to International Telephone and Telegraph Corporation, Nutley, N.J., a corporation of Maryland a t .Appli cation February 25, 1955, Serial No. 490,472

' 1 Claimsl Cl. 250-27 This invention relatesv to deflection circuits for cathode ray type electron discharge devices and more particularly to a means for automatically damping oscillations due to reversalof sweep voltages in the output transformer of I deflection waveform generators employed in television and like apparatus.

. This is due to thetinductive kickf or voltage across the primary winding inductance. This may cause ringing or oscillatory currents which may carry over into the sweep periodrand affect signal reproduction.'

- The oscillatory currents established in the output transformer upon reversal of the sweep voltage has in the past been 'dampedby employing the plate resistance of the v tooth waveform into a trapezoidal form by what is known commonly asfpeaking. This peaking has been accomplished in the past inthe sawtooth generator discharge tube circuit ,by adding a fixed resistance peaking resistor The addition of this fixed resistor to a conventional sawtooth generator produces an additional pulse which is superimposedupon the retrace portion of, the deflecting waveform. -This addedpulse determines the plate resistance of the output or driver tube of the deflection system during the retrace portion and the start of the sweep portion of the deflecting waveform to establish thedamping elfect on,the oscillations present in the output transformer.

The amount of damping provided by the driver tube is rather critical. Too much or too little damping will not have the desired effect of suppressing the unwantedoscillations and may affect the retrace time long enough to pulses is present, when a given set of tubes are employed,

when a given value of B'| voltage is present, and for receiver, the change of anyone of these conditions ora ,combination of these conditions will vary'the amount 2,927,998 Eatented Mar. 8, i960 bias voltage of the peaking electron discharge device proportional to the peak amplitude of the deflection waveform appearing at the output of the deflection system so that automatically the correct amount of damping results,

regardless of the signals passingthrough the system.

A further feature of this invention is the employment i of a peak detector to monitor the peak amplitude of the deflection waveform appearing at'the'output of the deflection system, the output of the peak detector adjusting the bias of the peaking electron discharge device disposed in serial relation with the charging condenser of asawtooth. generator to provide a variable peaked sawtooth output therefrom to adjust the plate resistance of the output tube in a manner to maintain a constant damping effect on the oscillations within. the output transformer deflection system. The above-mentioned and other features and objects 'of'this invention will become more apparent by reference to the following description taken'in conjunction with the accompanying drawing, the sin'gle figure of which illustrates schematically an embodiment of our invention.

' In the drawing, there is illustrateda portion of a deflection circuit comprising a sourceiiof pulses 1 wherein the output therefrom, as illustrated by curve 2, is repetitious ata predetermined ratefor control" of the operation of a trapezoidal waveform generator 3. For purposes of explanation, the portion of the deflection circuit illustrated is thatof a vertical deflection circuit employed in a'television receiver'and the' o utput of source 1 is repetitious at the field scanning rate. It is to be understood that the automatic damping circuit disclosed herein may be utilized inany comparable deflection system having a similar damping problem; v

- The trapezoidal waveform generator 3 'inclildestherein a normally non-conducting electrondischarge-device or tube 4 and an RC time constant including charging con denser 5, load resistorfi and the plate resistance of electron discharge device ortube-7. Resistor 6 also serves tosupply voltage from'the B -jsupply to the anode 8 of'tube 4. When a positive synchronizing pulse from source 1 is coupled through condenser 9 to grid 10 of tube 4, the tube becomes conductive. The capacitor 5 at this time immediately discharges to ground through regardless of theamplitude of' the signals within'the the internal plate resistance of tube 4. Tube 4 behaves a certain setting'of the heightcontrol in a television I like a switch-between condenser 5 and ground. When the synchronizing pulse is removed, grid'10 returns to some negative potential cutting off tube 4 and thereby terminating the discharge of condenser 5. Condenser 5 of damping presented to the oscillations in the output transformer.- a v r Therefore, itis an object of this invention to provide a means to automatically maintain a constant damping of the oscillations occurring in the output transformer of a deflection system. t i' I Another objectof this invention is to provide an electronically "controlled trapezoidal waveform generator which'gwill automatically provide a constant damping of the oscillation mime output transformer.

featu'rs of invention is the provision .of a varistarts to charge towardthe value of the B+ supply at aneXponential-" rate depending primarily upon the values of condenser 5:;and resistor 6. v

Tube 7 is placed in series with condenser 5 toprovide a variable peaking resistor by controlling its conduction and, hence, its plate resistance. The anode potentialfor tube 7 is provided by resistor 11 disposedbetween the B+ supply and the anode 12 of tube 7. .With tube 7 biased to obtain a given plate resistance, the output of generator 3 is coupled from point 13 through condenser :lfi to grid 15 of the output electron discharge device 3 a of tube 16 substantially in the form as indicated by waveform 17. The peaked sawtooth or trapezoidal waveform will be amplified by tube 1.6 and coupled to the primary winding 18 of the output transformer 19. To enable the desired automatic control of the damping effect accomplished by the plate resistance of tube 16, a vacuum or semiconductive diode 20 is placedacross the secondary winding 21 of output transformer 19. The diode 20 functions as a peak detector whose conduction varies in accorclance with the value of the positive pulses occurring in the secondary winding 21. When the amplitude of the output signal increases, the diode 20 conducts a greater current and develops a control signal in the form of a positive bias voltage across resistor 22. This bias v l a e ac n i u 7 to increa e t nd ct er t re? nd hu dec ea its Pla e r t n e- T decre ed plate e is an e re u ts in a ecreased amoun 9? P akin n the t anczcida wa ef m Th e re s t aci litt d c the p a d pa t es cfthe defl t on age pr id s a ce rcti e dam n eff c by r isin t e 91?? l e 011 r 15 of 15? 6- T s nc a h c nd fimi' e t ush and u s i a l w r pl resistance for tube 16.

Conversely, a signal amplitude decrease at the secondary winding 21 will decrease the conduction through diode 20, thus, a less positive voltage across resistor 22, and, hence, a less positive bias on grid 23 of tube 7. This results in less conduction through device 7 and an increase in plate resistance therein. A higher plate resistance for tube 7 produces an increased peaking pulse at point 13 which will bias grid 15 of tube 16 more negative resulting in decreased conduction through tube 16 and thus an increase in its plate resistance to provide the necessary corrective damping. This maintenance of constant effective plate resistance assures correct damping on the output transformer 19.

The action above outlined may seem opposite to what may at first be inferred. However, this is reconciled by the fact that as the sawtooth amplitude is increased, the damping effect is also increased due to the tendency of tube 16 to draw anode current under higher voltages. The damping due to plate resistance is a dynamic quantity which depends upon the characteristics of tube 16 during the retrace period. At this time, two pposin actions take place. First, grid 15 is being driven negative by the combined sawtooth and peaking pulse, the

net result being an increase of plate resistance. Second, the added effect of the peaking pulse produces a relatively high induced voltage across anode 2 4 of tube. 16. This voltage tends to produce a decrease in plate resistance particularly it anyanode current flows. The decrease plate resistance due to the induced voltage at anode 2 t overshadqws any increase of plate resistance due to the action of the driving waveform at grid 15.

The above-described automatic damping circuitwill result in a constant damping effect of the oscillation occurring in the output transformer of a deflectionwaveform generator due to the sudden reversal of sweep currents therein regardless of amplitude signal variations occurring in the deflection waveform generator. This constant damping provides the advantage of a deflection waveform having uniform retrace and sweep time;

While we have described above the principles of our invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of our invention as set forth in the'objects thereof and in the accompanying claims. i

l. A circuit for generating the. deflection voltage for a deflection'system of a cathode ray type electron dis-- charge device which automatically maintains a constant damping of the oscillations in said defiection system comprising a source of repetition pulse signals, a reactive means to produce a sawtooth waveform having a sllb 4 stantially linear sweep portion and a retrace portion in synchronism with said pulse signals, a variable resistance means coupled to said reactive means to provide a series circuit to peak said sawtooth waveform during the retrace portion thereof, said series circuit being coupled in shunt relation to said source, an output means including an electron discharge device for coupling the peaked sawtooth waveform from said reactive means, a detector means coupled to the output of said discharge device to develop a control signal in accordance with the peak amplitude of said peaked sawtooth waveform, and means to couple said control signal to said variable resistance means.

2. A waveform generating circuit for a deflection system of a cathode ray type electron discharge device comprising a source of synchronizing pulse signals, a time constant network including a condenser and a variable resistor, said variable resistor being coupled to said condenser to provide a series circuit, said series circuit being coupled in shunt relation to said source, means responsive to said pulse signals to synchronously charge and discharge said time constant network to produce a peaked sawtooth waveform, an output circuit including an electron discharge device to remove the peaked sawtooth Waveform from said time constant network for coupling to a deflection system, apeak detector coupled to the output of said discharge device fordeveloping a control signal in accordance with the peak amplitude of said peaked sawtooth waveform, and means to couple said control signal'to said variable resistor to vary the resistance thereof proportional to the amplitude level of said peaked sawtooth waveform for control of the peak amplitude of said sawtooth waveform to maintain a substantially-constant damping of the oscillations induced in said output circuit regardless of signal variation in said time constant network.

3. A waveform generating circuit for a deflection system of a cathode ray type electron discharge device comprising a source of synchronizing pulse signals, a reference potential, a time constant network including a charging condenser and a first electron discharge device having at least an anode, a cathode and a control grid, the cathode of said first device being coupled to said reference potential and the anode of said first device being coupled-to one side of said condenser, means coupled to the other side of said condenser and responsive to said pulse signals to synchronously charge and discharge said time constant network to produce a peaked sawtooth waveform, an output circuit including asecond electron discharge device to remove the peaked sawtooth waveform from said time constant network for coupling to a defiection system, a peak detector coupled to the output of said second discharge device for developing a control voltage in accordance with the peak amplitude of said peaked sawtooth waveform, and means to couple said control voltage to the control grid of said electron discharge device to vary the plate resistance thereof inversely proportional to the amplitude level of said peaked sawtooth waveform for control of the peak amplitude of said sawtooth waveform to maintain a substantially constant damping of the oscillations induced in said output circuitregardless of signal variations in said time constant network.

4. A waveform generating circuit for a deflection system of a cathode ray type electron discharge device comprising a source of synchronizing pulse signals, a reference potential, a time constant network including a condenser and an electron discharge device having at waveform, an output circuit to remove thepeaked sawtooth waveform from said. time constantmetwork for coupling to a' deflection system, a unidirectional device and a resistorcoupled in a series relationship acrossfthe output of said output circuit for developing a control voltage in accordance with the peak amplitude 'of said peaked sawtooth waveform, and a conductor coupled to the junction of said unidirectional device and saidresistor to couple said control voltage to the. control grid ofsaid electron discharge device to vary the plate resistance thereof inversely proportional to the amplitudelevel of said peaked sawtooth waveform for control of the peak amplitude of said sawtooth waveform to maintainta substantially constant damping of. the oscillations induced in said output circuit regardless of signal variations in said time constant network.

5. A circuit for generating the deflection voltage for a deflection system of a cathode ray type electron discharge device which aufomatically maintains a constant damping of the oscillations in saiddeflection system comtron-discharge device having at least an anode, cathode electron discharge device to render said first electron disprising a first electron discharge device having at least an anode, a cathode and a control grid, said first.elec-' cathode of said first electron discharge device, a series circuit including a charging condenser and a variable resistancemeans coupled between the anode of said first electron discharge device and said reference potential, said load resistor and said variable resistance means providing the charging path for said charging condenser, a source of synchronizing pulse signals, means coupling said synchronizing pulse signals to the cathode of said first electron discharge device to render said first electron discharge device conductive in synchronism with said synchronizing pulse. signals, the conductive path of said first electron discharge device and said variable resistance means providing the discharge path for said charging condenser to produce a peaked sawtooth waveform, an output means including a second electron discharge device and an output transformer to remove the peaked sawtooth waveform from the anode of said first electron discharge device, the plate resistance 'of said second electron discharge device damping the oscillations in said output transformer, peak detector means coupled to said output transformer to develop a control signal in accordance with the peak amplitude of said peaked sawtooth waveform and means to couple said control signal to said variable resistance means to vary the resistance thereof inversely proportional to the amplitude level of said peaked sawtooth waveform 'for control of the plate resistance of said second electrondischarge device to main tain a substantially constant damping effect on the oscillations induced in said output transformer regardless of signal variations in the signal at the anode of said first electron discharge device.

6. A circuit for generating the deflection voltage for a deflection system of a cathode ray type electron discharge device which automatically maintains a constant damping of the oscillations in said deflection system comprising a first electron discharge device having at least an anode, a cathode and a control grid, said first electron discharge device being normally nonconductive, an anode voltage supply source, a reference potential, a load resistor coupled between said voltage supply source and the anode of said first electron discharge device, a bias resistor coupled between said reference potential and the cathode of said first electron discharge device, a series circuit coupled between the anode of said first electron discharge deviceand saidfreference potential, said series circuit including a charging condenser and a second eleccharge device conductive'in synchronism with said synchronizing pulse signals, the conductive path of said first electron discharge device and said second electron discharge device providing the discharge path for said charging condenser to produce a peaked sawtooth waveform, an output means including a third electron discharge device having at least a cathode, an anode and a control grid and an output transformer coupled to the anode of said third electron discharge device to remove the peaked sawtooth waveform from the anode of said first electron discharge device, the plate resistance of said third electron discharge device providing a damping effect for the oscillations in said output transformer, peak detector means coupled to said output transformer to develop a control voltage in accordance with the peak amplitude of said peaked sawtooth waveform, and means to couplesaid control voltage to the control grid of said second electron discharge device to vary the plate resistance thereofvinversely proportional to the amplitude level of said peaked sawtooth waveform for adjustment of the plate resistance of said third electron discharge .prising a first electron discharge device having at least an anode, a cathode and a control grid, said first electron discharge device being normally nonconductive, an anode voltage supply source, a reference potential, a load resistor coupled between said voltage supply source and the anode of said first electron discharge device, a bias resistor coupled between said reference potential and the cathode of said first electron discharge device, a series circuit coupled between the anode of said first electron discharge device and said reference potential, said series circuit including a charging condenser and an electron discharge device having at least an anode, cathode and control grid, the anode and cathode thereof being in series relationship with the charging condenser, said load resistor and said second electron discharge device providing the charging path for said charging condenser, a source of synchronizing pulse signals, means coupling said synchronizing pulse signals to the grid of said first electron discharge device to render said first electron discharge device conductive in synchronism with said synchronizing pulse signals, the conductive path of said first electron discharge device and said second electron discharge device providing the discharge path for said charging condenser to produce a peaked sawtooth waveform, an output means including a third electron discharge device having at least an anode, a cathode and a control grid and an output transformer coupled to the anode of said third electron discharge device to remove device and said resistor to couple said control voltage to the control grid of'said second electron discharge device to vary the plate resistance thereof inversely proportional to the amplitude level of said peaked sawtooth waveform for control of the plate resistance of said third electron discharge device to maintain a substantially constant damping eflfect on the oscillations induced in said output transformer regardless of signal variation in the References Cited in the file of this patent signal at the anode of said first electron discharge device. 10 2,728,875

UNITED STATES PATENTS Ames et a1. Aug. 31, 1948 Custin May 22, 1951 Wynn a Nov. 6, 1951 Woodrufi Dec. 1, 1953 Volz July 27, 1954 Casey Nov. 30, 1954 Kihn Dec. 27, 1955

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