US2344810A - Synchronization of deflecting circuits - Google Patents

Description

March 1944- e. L. FREDENDALL ETAL 2,344,319

SYNCHRONIZATION OF DEFLECTING CIRCUITS Filed Dec. 31 1941 2 Sheets-Sheet 1 AAAAAA AAAAAA March G. L. FREDENDALL ETAL ,3

SYNCHRONIZATION OF DEFLECTING' CIRCUITS Filed Dec. 31, 1941 2 Sheets-Sheet 2 wnzram a 4 +4 Patented Mar. 21, 19.44

[ .uNTao STATES- 7 23445810 4 srscnnomzarios or net-Lacuna CIRGUI Gordon L. Fredendall. Westmont, and Alfred c. Schroeder, Camden, N. 3L, as'signors to Radio Corporation of America, a corporation oi Delaware Application December 31, 1941, Serial naazsscs 8 Claims.

- Our invention relates to automatic frequency control or phase control circuits and particularly to the synchronization of cathode ray deflecting circuits in television receivers or the like.

The deflecting circuits of a television receiver usually contain an oscillator which is to be synchronized by incoming synchronizing pulses whereby the scanning at the receiver is held in Synchronism with that at the transmitter. It has previously been proposedthat this synchronization be obtained by employing an automatic frequency control circuit responsive to any change in the time relation of the synchronizing pulses and the saw-tooth waves deflecting circuit.

An object of the present invention is to provide an-improved synchronizing circuit of the above-described type. v

A further object or the invention is to provide animproved method of and means for synchronizing a cathode ray deflecting circuit.

produced by thement of our invention as applied to a television tively, the tube I0 being biased by the usual cathode resistor l2 and bypass condenser 63.

The tubes l0 and I! are resistance-capacity coupled by means of the video ampllfler's plate resistor M an'd peaking coil 16, a coupling condenser l1 and a grid leak resistor 68.

The control grid circuit of the cathode ray -tube H is completed through the cathode re- A further object of the invention is to provide an improved television synchronizing circuit that is not greatly aflected by noise in theincoming signal. v

A still further object of the invention is to provide an improved television receiver.

In a preferred embodiment of the invention,

the automatic'frequency control voltage is obtained by employing a pair of peak rectiflers connected in balanced relation which have a mixture of synchronizing pulses and saw-tooth signal to decrease. The resulting change in the peak rectifier outputs is utilized to control the frequency of the deflecting circuit oscillator.

The invention will be better understood from the following description taken in connection with the accompanying drawings in which" Figure l is a circuit diagram-of one embodisistor IQ of a vacuum tube 2i which functions both as a direct current or background inserter for the cathode ray tube and as a separating tube for passing synchronizing pulses only to the synchronizing or automatic frequency control circuits. of the saw-tooth wave'deflecting circuits as explained below.

The horizontal deflecting coils indicated at 82 and the vertical deflecting coils indicated at 23 are supplied with saw-tooth current from a nor izo'ntal deflecting circuit 25 and from a vertical deflecting circuit 240., respectively. These deflecting circuits may be of any suitable design. In the example illustrated, the deflecting circuit 24 includes a blocking oscillator which comprises a vacuum tube 21, a feedback transformer 23, a grid condenser 29 and a grid leak resistor The blocking oscillator pulses are applied to a discharge tube 32 of a conventional sawtooth wave generating circuit which includes condensers 33 and 34 that are charged through the plate resistor 36.

The saw-tooth voltage appearing across condensers 33 and 34 in series is applied toa high impedance output tube 31 which has its plate circuit coupled to deflecting coils 22 through the coupling condenser 38 and the choke coil 39.

The saw-tooth voltage across condenser 86 is also supplied by way of a. conductor M to the AFC circuit 42 for the horizontal deflecting circult 26.

Them circuit 82 comprises a transformer it I Thllillhfln in-I'igs. 4a and 4b (where the dihaving a primary M and a'secondary A resistor 67 across the secondary I! is connected signals). '1o simplify the drawings, the voltage at its midpoint to the conductor ll.

one end or secondary I8 is coupled through a condenser 49 to the cathode of'a diode" II: the other end is coupledthrough' a condenser II to I the plate of a diode B3.

The diodes BI and mesaaeim mswot peak rectiflers by giving the dischargejpaths oi:

condensers 49 and 52 a long time constant.'-. 'Ii1e discharge path condenser 48 a. res, I sistor'llconnected across diode II' and through a biasing battery or other suitable biasing source I are held at -the.refer-curse level of 1.5 volts in 56. The discharge path for condenser- '52 is" through a resistor 67 connected betweenthe plate I of diode 68 and ground.

The plate and the cathode of diodes Bi and 53, respectively, are held slightly negative with respect to ground by the biasing-source "as indicated.

The cathode of diode i and the plate of diode-- 53, each of which varies in D.-C. potentialjinfac cordance with the peak rectification, are conuxi iary filtering means comprising a resistor nected to opposite ends of a mid-tapped potentiometer comprising resistors 58 and 89, the said mid-tap being D.-C. connected to the grid oi an amplifier tube 8|.

As reviously indicated,- saw-tooth voltages;

fed into the AFC circuit 42- at the midpoint oi resistor W. The horizontalsynchronizing pulses are fed into this circuit through the transformer 48, the transformer having a suillciently poor frequency response to prevent-the transfer oi. the comparatively low frequency vertical synchronizing pulses. Also. the'transiormer preferably narrows the horizontal synchronizing pulse by dinerentiating them.

diode to rectify the peaks of synchronizing pulses which are eppliedtc said cathode with negative The tube 2i operates to remove the. picture 'Figs. 8a to signal and pass onlyvthe synchronizing pulses since its grid and cathode elements not as a f a. decrease-lathe an. amplitude out. other.

rect current component is shown included in the pulses can and centre not-shown as diflerentiatedpulses, -.only the portion of the pulse that spectively. These voltages include the D.-C.- voltage insertcdby the. peakrectifier action oi! the diodes "and ll.= More specifically, it will be noted that the peaks oi the synchronizing pulses the particular. example assumed.

' The signal appearing at-the midpoint F 01 the resistors and II is shown in Fig. 3e. It will be seen that the synchronizing pulses have been balancedouhleaving a signal containing only the D.-C. andsawtoothwave components. .This signal is amplifle'dbythe amplifier tube II which has in its plate circuit the usual-plate resistor 82 and. in addition, 'a'fllter condenser 63- and an potential is vunfi edthrough a-conductoi1 61 to the gridflofthe blockingoscillator tube Ilior controlling the blocking oscillator irequenoy.

The auxiliary filtering meansOL-BC is not necessary for satisiactory operation but it ishelpful in I noisy locations since it illters out random noise It-hasbeen assumed that'the deflecting circuit adjustment is such that it is held in synchronismunder the condition illustrated in Assume nowthat' the blocking a oscillator starts to slow down so that the phase relationoi the sawtooth waves and the synchronizing pulses-changes to that shown in Figs. 4a 'and 4b, thisparticular phase relation, incidentally; being a limiting condition. As a reapplied from the plateresistor l8 tothecathode suit. the 11-0. component as measured from the of tube 2i through a resistor 40 and a condenser fit whereby the rectified current charges condenser Eiil to a value which varies with the peak amplitude of the synchronizing pulses; The resistor 10 isolates condenser from the plate circuit of the video amplifier iilwhereby its ire-- quency'l'fismuse s n t imp iedr I will beun -I derstood that the discharge circuit .forcondenser Eli has a time'consiiantisuch that. most of the- I I 18 than before (compare with Fig. 3:). I

condenser charge holds" over betweensuccessive horizontal synchronizing'pulses 'gg m i .-,I

fled by the tube, 21 and applied tofa D.'-C. ampli-. I I I I I I The opposite-action isillustrated in Figs. 4d.

sound 4!. Since these figures its primary and secondary shuntedby condensers. I

83 and 9. respectively, for passing the cem 011mm pulses-only.

For a certain assumed phase relation of saw.- tcoth voltages andsyrichronizing pulses, the volt-v ages appearing at the, points 13 and oi the" 3 resistor 67 are shown in Figs. 3a and 3b, respec I I to In the vertical deflecting circuit parts corretively. The sawtooth voltages can at these points in the phase relation of the sawtooth wavesand the synchronizing pulses will cause anincrease in reference voltage of -l.5'volts is increased at point D and decreased at point Ens will be seen by comparing Figs. '3cfand 4a and by comparlng ,Figs. and 4b.. Or, considering the pogone: more negative. 'The potential at the midpoint r willbe intermediate these two potentials as shown at Fig. 4c and will be more negative sincejampliner tube n reverses the polarity of a signal, the -D.-C. control potential applied less negative and to the blocking oscillator is the oscillator is speeded up.

correspond to 1133-40, 4b and 4c they are self-explanatory.

I Comparing Figs. 4! and 3e, it will be seen that when the phase shift is in this direction the g; point Fgoes less negative with respect to ground whereby the blocking'oscillai'or will be'slowed down. A

The ioregoing description applies equally well to the vertical deflecting circuit shown at 42a.

noted that the vertical deflecting circuit. preithe peak amplitude of one composite signal and 1 crably includes the. n g w I each connected in balanced relation, a cathode sistor indicated at 15 which is in series with the sawtooth wave condensers and that it may also include a cathode resistor 16 for further improving the wave form of the deflecting current flowing through the vertical deflecting coils.

In Figure 2, there is shown a different output circuit for the peak rectifier diodes 5! and 53. The potentials at points E and D are applied to the grids of amplifier tubes H and 12 which have a common plate resistor 73 whereby the said potentials are added and applied to the filter condenser 63. The operation is similar to that previously described.

Values for. various circuit elements in Figure 1 are given below merely by way of example:

Condenser 8- ,mi Condenser 9 do a .01

Condenser 49 do .001 Condenser 52 do .001 Condenser 49a d .1 Condenser 52a do .1 Condenser B3 ..do 1 Condenser 66 do 100 Condenser 63a do- 1 Condenser 86a do.. 100

Resistor 41 ohms 16,400 Resistor 41a do 9,400 Resistor 54 megohms 4.7 Resistor do 4.7 Resistor 540 do 2.2 Resistor 51!: do 2.2 Resistor 58 ohms 100,000 Resistor 59 do 100,000 Resistor 58a. megohms 10 Resistor 59a do 10 Resistor 64 ohms variable" 10,000 Resistor 64a "do..-" 10,000

and having simultaneously sloping portions which slope in the same direction, superimposing with opposite polarity said synchronizing pulses upon said sloped portions, respectively, to produce a pair of resultant pulses, producing a frequency control voltage having a value which changes in responseto a change in the relativepeak amplitudes of said resultant pulses, and applying said control voltage to said oscillator to control its frequency.

2. In combination, a pair of peak rectifiers having input circuits and output circuits, an

oscillator and means for generating-a periodicircuits and for utilizing the combined output as a frequency control voltage which is applied to said oscillator.

3. In a television receiver, a pair of peak recti tiers having input circuits and output circuits ray deflecting circuit which includes an oscillator and which also includes means for generating a steep-sided wave occurring in a fixed time relation to theoscillator frequency, means for applying said wave to said rectiflers with like polarity at each rectifier, means for applying incoming synchronizing pulses to said rectiflers with the polarity at one rectifier opposite that at the other rectifier and in additive relation to said wave whereby a frequency control voltage appears in said output circuit, and means for utilizing said frequency control voltage to control the frequency of said oscillator.

4. A deflecting circuit having an oscillator therein, means for producing a pair of voltage waves having a definite time relation with respect to the frequency of said oscillator and having simultaneously sloping portions which slope in the same direction, means for superimposing received synchronizing pulses of opposite polarity upon said sloped portions, respectively,-to produce a pair of resultant pulses, means for producing a frequency control voltage having a value which changes in response to a change in the relative peak amplitudes of said resultant pulses, and means for controlling the frequency of said oscillator in accordance with said controlvoltage.

5. In a television receiver, a pairoi' peak rectifiers each having an input circuit and an output circuit, said input circuits being connected in balanced relation with respect to a source of syn-- chronizing pulses, a cathode ray deflecting circuit which includes an oscillator and means for generating a steep-sided wave occurring in a fixed time relation to the oscillator frequency, means for applying said wave to said rectifiers with like polarity at each rectifier whereby it is added to synchronizing pulses of one polarity at one of said rectifiers and is added to synchronizing pulses of the opposite polarity at the other of said rectifiers, and means for utilizing the output appearing in said output circuit as a frequency control voltage to hold said oscillator in synchronism with said pulses.

6. In a television receiver, a pair of peak rectifiers having input circuits and output circuits each connected in balanced relation, each of said rectifiers having an electrode which is brought to a certain direct current potential by the peak rectifier action, a cathode ray deflecting circuit which includes an oscillator and means for generating a steep-sided waveoccurring in a fixed time relation to the oscillator frequency, means for applying said wave to said rectifiers with like polarity at each rectifier, means for applying incoming synchronizing pulses to said rectifiers with the polarity at one rectifier opposite that at the other rectifier and in additive relation to said wave, said balanced output circuit connection comprising resistor elements connected between said peak rectifier electrodes, means for charging a filter condenser in accordance with the potential appearing at an intermediate point on said resistor elements, and means for utilizing the voltage across said filter condenser to control the frequency of said oscillator.

7. The invention according to claim 6 wherein each of said peak rectifiers comprises a diode and wherein one of said electrodes is a diode cathode and the other of said electrodes is a diode plate.

8. In combination, an oscillator, a source of periodically recurring synchronizing pulses, means for producing periodically recurring waves having a definite time relation with respect to the irequency of said oscillator and each having a sloping portion, a pair or rectifier-s, means for applying said waves with like polarity to said rectiners, means for superimposing with opposite polarity synchronizing pulses from said source upon said sloped portions oi said waves at said rectifier-s, respectively, to'produce a pair of resultant pulses, means including said rectii'iers for producing a frequency control voltage having a value which changes in response to a change in the relative peak amplitudes 01' said resultant pulses, and means for applying said control voltage to said oscillator to control its frequency. V

GORDON L. IREDENDALL. ALFRED C. BOHROEDER.

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