US2354032A - Synchronizing pulse separating circuit - Google Patents

Description

July 18, 1944. H r,.| YMAN sYNcHRoNIzING PULSE SEPARATING CIRCUIT Filed Jan. 19, 1945 impair/ms M0 l l l H l l l l l l l l l Inventor. Harold Tl/man.,

y His Attorney I ratus with the sending apparatus.

Patented Julv 18,

sYNcnaoNlzlNG PULSE SEPARATTNG cmccrr Harold T. Lyman, Milford, Conn., assignor to General Electric Company, a corporation of New York Application January 19, 1943, Serial No. 472,839 s claims. (ci. 11s-1.5)

My invention relates to television systems and the like and particularly to circuits employed in television receivers for separating the synchronizing pulses from the remaining portion of the signals and for separating the line and frame synchronizing pulses.

In television systems at the present time cathode ray tubes are employed both in the transmitter and in the receiver, and it is essential that the incremental areas traversed by the transmitter and receiver cathode ray beams 'correspond exactly in time and position. For this reason it is necessary to synchronize the receiving appa- In order to accomplishthis, synchronizing signals or pulses are transmitted on the same carrier as the picture or video signals, the synchronizing pulses being introduced during the blanking or pedestal periodswhen the cathode ray beam is being returned to start another line. or another frame of the picture. The synchronizing signals are superposed on the blanking signals and the line and' frame signals are -of the same amplitude. The line synchronizing pulses occur at the end of each line of the picture and the frame synchronizing pulses at the end of a group of lines corresponding to one frame of the picture. The line synchronizing pulses are of short duration and the frame synchronizing pulses are of longer duration so that they may be separated respectively by differentiation and integration of the signal, thereby providing line synchronizing pulses of high frequency and frame synchronizing pulses of low frequency. The line pulses are employed. to energize a saw-tooth wave generator for actuating the horizontal deecting members of the cathode ray picture tube, and the frame synchronizing pulses are employed to energize a sawtooth wave generator for actuating the vertical deecting members of the cathode ray picture tube. The frequency of the line or horizontal synchronizing pulses is much higher than that of the frame or vertical synchronizing pulses. For example, the line frequency may be 15,750 cycles per second and the frame frequency 60 cycles per second. It is necessary not only to separate the synchronizing signals from the picture signals but also to separate the vhorizontal and vertical synchronizing signals. Interference or cross-modulation of the horizontal pulses may be produced by the low frequency vertical pulses in such a manner that there is a substantial I variation in the amplitude of the horizontal pulses, and loss of synchronism may result. Accordingly it is an object of my invention to provide a television apparatus or thelike including an improved arrangement for separating line vand frame synchronizing pulses without crossmodulation of one group of pulses by the other.

It is another object of my invention to'provide a television apparatus or the like including an improved pulse separator for obtaining both the line and frame synchronizing pulses from a single amplifier or electron discharge device.

The novel features which I believe to be characteristic of my invention are set forth with par-v ticularity in the appended claims. My invention itself, however, both as to its organization and method of operation together with further objects and advantages thereof may best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 illustrates a television receiver including a synchronizing signal separator embodying my invention, and Fig. 2 illustrates a modiflcation of the separator shown in Fig. l.

Briefly the television receiving apparatus illustrated in the drawing comprises suitable detectors and amplifiers for receiving and amplifying the standard television signal and for impressing the picture or video signal upon the control electrode of a cathode ray picture tube and for clipping and separating the synchronizing pulses from the remainder of the signal and then separating the line and frame synchronizing pulses to drive cuit. The constant impedance network provides constant impedance over a wide range of frequencies including the frequencies of the line and frame signals and cross-modulation of the line signals by the frame signals is prevented which, otherwise, might be caused by non-linear control grid-anode characteristics and a varying impedance.

Referring now to the drawing, the television receiver illustrated in Fig. 1 comprises a cathode ray picture tube l0 having a cathode' Il and a control electrode or grid I2. Video or picture signals are impressed upon the tube lll between the cathode Il and grid I2 from a suitable receiving apparatus. 'I'he receiving apparatus comprises an antenna I3, radio frequency amplifying and converting apparatus Il, intermediate frequency amplifying and detecting apparal tus l5, and a video amplifier I6. The picture tube Ill is also provided with horizontal deiiecting members orcoiis I1 and vertical deflecting members o r coils I8. ergizing the coils l1 and Il are supplied from a vertical or frame deflection saw-tooth wave generator 20 and the deflection waves for energizing The deection waves for enthe coils |1 are supplied from a horizontal line deflection saw-tooth wave generator 2|. The synchronizing `signals or pulses for actuating generators 20 and 2| are obtained by supplying a signal from the intermediate frequency ampliiier and detector l to a synchronizing signal clipper and amplifier 22 which separates the synchronizing pulses from the remainder of the signal and then supplies them to a synchronizing pulse separator 23, which includes the circuit enclosed within the dotted line 24. The

. pulseseparator 23 includes an electron discharge device 25 having a cathode 26 and a control electrode or grid 21 and an anode 28. The amplified pulses from the clipping apparatus 22 are impressed upon the control electrode 21 which is coupled to the apparatus 22 by a condenser 30 and a resistance 3|. The device 25 is provided with a cathode resistor 32 and a by-pass condenser 33 for providing the desired bias for the control electrode 21.' In the anode circuit of the device 25 there is connected a constant impedance network 34 including two branches or sections 36, 31 and 38, 39 arranged in parallel. An ode voltage is supplied from a suitable source such as a. battery 40. A condenser 4| is connected across the battery '40 to by-pass the alternating current components of the load current.

One of the branches of the network 34 is capacitive and includesfa resistance 36 and a condenser 31 connected in series, the other branch is inductive and includes a resistance 38 and an inductancelcoil 39 connected in series. The resistance 36 and condenser 31 constitute an integrating circuit, the junction between the resistance and the condenser being coupled tothe frame deflection generator 20 through a condenser 42. The inductive branch including the resistance 38 and the coil 39 constitutes a differentiating circuit, the junction between the resistance and coil being coupled to the line defiection generator 2| through a condenser 43. The values of the resistances 36 and 38, the capacity of the condenser 31, and the inductance of the coil 39 are selected so that the impedance 0f the network 34 remains constant over a wide range of frequencies including,the frequencies of the line and of the frame synchronizing pulses.

Electron discharge devices such as the tube 25 have non-linear characteristics such that a change in the load which is supplied produces distortion of the signals; the use of the constant impedance network prevents or minimizes this distortion. The network 34 is of a type known in the art and its constant impedance characteristic is obtained by making theresistances 36 and 3B of the same value and equal to the square root of the ratio of the inductance of the coil 39 to the capacity of the condenser 31. The effective resistance of the network is the same as that of the resistances 36 and-38, thus:

-scribed above, the major portion of the voltage swing representing the frame lpulses appears across the condenser 31 and the major portion ofthe swing representing the line pulses appears across the coil 39. The line and frame synchronizing pulses are effectively separated and the relative amplitudes are maintained sc that both the generators and 2| continuously remain in synchronism with the received signal.

The modified form of the pulse separator shown in Fig. 2 is similar to the separator 24 shown in Fig. 1 and corresponding parts have been designatedby the same numerals. In Fig. 2 the network 45 is connected in the anode circuit of the device and comprises an inductive branch including a coil 46 and a resistance 41 and a capacitive branch including a condenser 48 and a network 49. The network 45 has the same characteristic as the network 34 of Fig. 1 so that the impedance of the load circuit of the device 25 remains constant over a wide range of frequencies. The coil 46 and resistance 41 connected in series to form the upper branch of the coil constitute an integrating circuit so that the low frequency vertical or frame synchronizing pulses appear across the resistance 41 and are coupled to the generator 20 through the condenser 42. The condenser 48 and network 49 are connected to provide a differentiating circuit so that high frequency line synchronizing pulses are coupled to the generator 2| through the condenser 43. The network 49 is a constant impedance network comprising two branches, one including a coil 50 and a resistance 5| in series and the other a condenser 54 and a resistance 55 in series. The total effective resistance of the network 49 is equal to the resistance 41. The resistances 5| and 55 are also equal lin value to the resistance 41, and the square root of the ratio of the inductance of the coil 50 to the capacity of the condenser 54 is equal to the square root of the ratio of the inductance of the coil 46 to the capacity of the condenser 48. By providing c the network 49 in the capacity branch of the network 49 and by coupling the generator 2| through the condenser 43 to the juncture of the condenser 54 and the resistance 55 still further separation of the line synchronizing pulses from the frame synchronizing pulses is obtained since the low frequency framesynchronizing pulses will tend to pass through the inductive branch of the network 49 v'including the coil 50 and the impedance 5|, and the high frequency line synchronizing pulses appearing across the resistance 55 will be free of any noticeable interference from the low frequency frame pulses. The network 43 constitutes a resistance element of the network 45, the resistance 41 being the other resistance element. y

Obviously a network similar to the network 43 may be substituted for the resistance 41 to fur;

therl minimize any iniiuence of the high frequency pulses on the low frequency frame pulses.

From the foregoing, it is readily apparent that I have provided a simple and effective circuit for separating high frequency line synchronizing pulses from low frequency frame synchronizing pulses, which circuit employs a single electron discharge device and operates without distortion of either group of pulses due to the presence of the other in the load circuit of the device.

While I have shown and described a particular embodiment of my invention in connection with a television receiver other applications will readily be .apparent to those skilled in the art. I do not therefore desire my invention to be limited to the particular circuits described and I intend in the appended claims to cover all modications Within the spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse separator for cathode ray television apparatus and the like comprising a thermionic ampliiier, a source of .line and frame synchronizing pulses, means for impressing said pulses on the input of said amplifier, a substantially constant impedance network comprising first and second parallel branches connected in the load circuit of said amplifier, said rst branch comprising an inductance and a resistance in series and said second branch comprising a capacity and a resistance in series, one of said branches constituting a dierentiating circuit, each of said resistances being equal to the square root of the ratio of the inductance to the capacity, and means responsive to voltage produced in said one branch for generating high frequency line deiiection waves in synchronism with said line l.

pulses.

2. A pulse separator for cathode ray television apparatus and the like comprising a thermionic amplifier, a source of line and frame synchronizing pulses, means for impressing said pulses on the input of said amplifier, a substantially constant impedance network comprising first and second parallel branches connected in the load circuit of said amplifier, said first branch comprising an inductance and a resistance in series and said second branch comprising a capacity and a resistance in'series, one of said branches constituting a differentiating circuit and the other of said branches constituting an integrating circuit, each of said resistances being equal to the square root of the ratio oi' the inductance to the capacity, means responsive to voltage produced in said one branch for generating high frequency line deilection waves in synchronism with said line pulses, and means responsive to voltage produced in said other branch for generating low frequency frame deflection waves in synchronism with said frame pulses.

3. A pulse separator for cathode ray television apparatus and the like comprising an electron discharge device including a cathode and an anodeand a control electrode, a source of line and frame synchronizing pulses, means for impressing said pulses on said control electrode, a substantially constant impedance network comprisingI first and second parallel branches connected between said anode and said cathode, saidrst branch comprising an inductance and resistance in series and said second branch com-v prising a capacity and resistance in series, one of said branches constituting a differentiating circuit and the other of said branches constituting an integrating circuit, each of said resistances being equal to the square root of the ratio of the inductance to the capacity, means responsive to the voltage produced in said one branch for generating high frequency line deflection waves' in synchronism with saidl line pulses, and means responsive to voltage produced in said other branch for generating low frequency frame deflection waves in synchronism with said frame pulses.

circuit of said amplifier, said network comprising rst and second sections connected in parallel, said first section comprising a rst inductance and a resistance in series, said second section comprising a first capacity connected in series with a parallel circuit having two branches, one vof said branches comprising a second inductance and a resistance in series and the other a Second capacity and a resistance in series, the ratios of said first and second inductances respectively to said iirst and second capacities being equal and all of said resistances being equal to the square root of said ratio, means responsive to voltage produced in said first section for generatingv low frequency frame deflection waves in synchronism with said frame pulses, and means responsive to voltage produced in lsaid other branch for generating high' frequency line deflection waves in synchronism with said line pulses.

5. A pulse separator for cathode ray television apparatus and the like comprising a thermionic frame pulses, each of said branches having a re sistance equal to the square root of the ratio of the inductance of the inductive branch to the capacity of the capacitive branch, means responsive to voltage produced in one of said vbranches for generating high frequency line deflection waves in synchronism with said line pulses, and means responsive to voltage produced in the other of said branches for generating low frequency frame deflection waves in synchronism with said frame pulses.

6. A pulse separator for cathode ray television apparatus and the like comprising a thermionic ampliiier, a source of line and frame synchronizing pulses, means for impressing said pulses on the input of said ampliner, a substantially constant impedance network comprising an induc- 4. A pulse separator for cathode ray television l apparatus and the like comprising a thermionic amplifier, a source of line and frame synchroniz- .ing pulses, means for impressing said pulses on tive branch and a capacitive branch in parallel connected in the load circuit of said amplifier, resistance elements in each of said branches, the resistance of said resistance elements being equal to the square root of the ratio of the inductance of said inductive branch t0 the capacity of said capacitive branch, one of said resistance elements comprising a substantially constant impedance network including two sections in parallelone comprising a condenser and a resistance in series and the other an inductance and a resistance in series, each of said resistances being equal to the resistance of said resistance elements and the ratio of the inductance of said other section to the capacity of said condenser being the same as said rst mentioned ratio, means responsive to voltage produced in one of said branches for generating low frequency frame de'ilection waves in synchronism with said framd pulses, and means responsive to voltage produced in the other of said branches for generating high frequency line

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