US2183966A

US2183966A - Periodic wave-generating system

Info

Publication number: US2183966A
Application number: US181129A
Authority: US
Inventors: Harold M Lewis
Original assignee: Hazeltine Corp
Current assignee: BAE Systems Aerospace Inc
Priority date: 1937-12-22
Filing date: 1937-12-22
Publication date: 1939-12-19
Anticipated expiration: 1956-12-19
Also published as: FR847870A

Description

Dec. 19, 1939.

H. M. I Ewls PERIODIC WAVE-GENERATING SYSTEM Filed Dec. 22, 1937 2 Sheets-Sheet 1 ATTORNEY Dec. 19, 1939. H. M. LEwls PERIODIC WAVE-GENERATING SYSTEM Filed Dec. 22, 1937 2 Sheets-Sheet 2 ...ll-1li...4 u

INVENTOR H ROLD M. LEWI @ma Vo .3a. o 1o.... i L f n f f r n u r r n r f r f f f n f f r o mda Mu) o .N61

ATTORNEY Patented Dec. 19, 1939 UNITED STATES PATENT OFFICE Harold M. Lewis, Great Neck, N. Y., assigner to Hazeltine Corporation, a corporation of DelawareA Application December 22, 1937, Serial No. 181,129

9 Claims.

This invention relates to periodic wave-generating systems. The invention is especially concerned with the provision of a wave-generating system for developing a scanning-synchronizing signal for use in a television system.

In accordance with present television practice, there is developed and transmitted a signal which comprises a carrier wave, modulated during recurring intervals or trace periods by video-frequency components representative of light and shade values of an image being transmitted. During the retrace intervals, between the trace periods, the carrier wave is modulated by a composite synchronizing signal which comprises im- 1" pulses or components corresponding to the initiations of successive lines and elds in the scanning of the image. At the receiver a beam is so deflected as to scan and illuminate a target in a series of successive elds of parallel lines, the video-frequency components of the signal being utilized to control the intensity of the beam. The line-synchronizing and field-synchronizing components are separated from the video-frequency components and from each other and utilized to 25 synchronize the operation of the receiver linescanning and field-scanning apparatus with the corresponding apparatus utilized at the transmitter in developing the signal. The transmitted image is thereby reproduced on the target of the receiver.

In scanning of the interlaced type, line and field frequencies are so related that successive fields are staggered, the lines of one fleld falling between or interlacing those of a preceding field 35 and, due to persistence of Vision, an optical effect is produced as though each field comprised a multiple of the actual number of lines scanned per eld.

Various types of synchronizing signals and ap- 40 paratus for developing them have heretofore been proposed, the type of signal required ordinarily being dependent upon the type of scanning utilized. Where interlaced scanning is employed, certain of the field-synchronizing impulses must 45 occur between line-synchronizing impulses and,

in order that the line-synchronizing and framesynchronizing impulses of the composite synchronizing signal may be successfully separated from each other and utilized, a special type of 5o synchronizing signal is required. One such type of signal which has been proposed comprises line-synchronizing and frame-synchronizing impulses of the same amplitude, but with the latter of substantially longer duration than the former 55 and serratedto permit uninterrupted recurrence (Cl. Z50-$6) of the former. Such a signal may be developed by generating a line-synchronizing impulse wave of the desired frequency and, in addition, generating a similar alternate-impulse wave and a parabolic-impulse wave, the alternate wave being 5 of the line-scanning frequency but having its impulses so displaced in phase as to occur between the line-synchronizing impulses, and the parabolic wave being of double the line-scanning frequency with its impulses in such phase as to occur intermediate the line-synchronizing and alternate impulses. These three waves may then be periodically combined at field-scanning frequency intervals and for predetermined durations, thereby to produce the desired serrated fleld-synchronizing impulses, Certain difculties, however, are presented in the development of the several waves in the precise synchronism required to procure the necessary phase relationships, this being particularly true with regard to the linesynchronizing and alternate-impulse waves.

It is an object of the present invention, therefore, to provide an improved periodic composite impulse wave-generating system.

More particularly, it is an object of the invention to provide a system of the character described whichis especially adapted in developing a composite synchronizing signal for use in a television system.

In accordance with the present invention there is provided a. periodic wave-generating system which comprises means for generating a first periodic-impulse wave of a predetermined fresecond waves. This later means may comprise 5 a direct connection between the two generating means for controlling the operation of one in accordance with the operation of the other.

Each of the generating means may comprise energy-storage means with charging and discharging circuits therefor and suitable control means, such as a vacuum tube, for controlling these circuits to eiect periodic charging and discharging of the storage means. The control conmotion between the two generating means preferably serves to disable one circuit of one of thc generating means during operation of the corresponding circuit of the other of the generating means. An arrangement for generating wave forms of the general type of those utilized in the present invention and which, per se, forms no part of the present invention is disclosed and broadly claimed in a copending application of Madison Cawein, Serial No. 176,963, filed November 29, 1937, and assigned to the same assignee as the present application. o

For -a better understanding of the invention, together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and itsscope will be-pointed out in the appended claims.

In the accompanying drawings, Fig. 1 is a circuit diagram, partially schematic, of a complete television transmitting apparatus embodying the invention; while Figs. 2-7, inclusive, are curves illustrating the wave forms of periodic waves developed at various points of the system of Fig. 1 to aid in the understanding of the invention.

Referring now more particularly to Fig. llof the drawings,` there is illustrated a television transmitting system comprising a cathode-ray signal generator I0, which may be of a conventional design and include the usual 'signal-generating tube, camera, and scanning elements.v

For the purpose of developing scanning voltages or currents for the generator I0, there are provided .a line-frequency saw-tooth wave generator II and a field-frequency saw-tooth wave generator I2, the output circuits of these generators being connected to the scanning elements of the.

signal generator ID in the usual manner. In order to blocli out the cathode ray of the generator I0 during the retrace scanning periods, there is provided a block-out wave generator I3 having its output circuit suitably connected to the signal generator I0. For providing pedestal impulses to suppress undesirable signal impulses during retrace scanning periods and to ensure the proper form of the modulation signal to be developed, there is provided a pedestal-impulse generator I4 and, in order to develop a composite scanning-synchronizing signal in accordance with the present invention, there is provided a synchronizing signal generator I5. The generator I5 comprises a line-synchronizing impulse-wave generator I6, an alternate-impulse wave generator I1, a parabolic-impulse wave generator I8, and a signal-combining network I 9. Suitable control circuits 20 and 2| are provided in connection with the combining network.4 For the purpose of synchronizing the generators I I-I4, inclusive and lli-I8, inclusive, and the control circuits 20 and 2|, there is provided for the system a timing-impulse generator 22 to which are coupled the input circuits of the last-mentioned generators and control circuits. Preferably, the generators I6I8, inclusive, are all connected to a, single output circuit of the generator 22, across which is developed a periodic synchronizing-impulse wave of double the desired line-scanning frequency, for example, 26,460 cycles for 441 line interlaced scanning with a field frequency of 60 cycles.

In accordance with the present invention as hereinafter described, the generators I6 and I1 are arranged to be individually synchronized by successive impulses of the double-frequency wave, while the parabolic-impulse wave generator I8 develops -a wave of the double frequency and is synchronized by all of the impulses of the timing wave from generator 22. The generator 22 is preferably stabilized by means of a connection 23 to a suitable source of periodic voltage, for example, the power supply circuit or the synchronizing source of motion picture mechanism,where such is employed.

Connected in cascade to the output circuit of the cathode-ray signal generator I0, in the order named, are video-

frequency ampliers

24, 25, and 26, a modulator 2l and'asso'ciated coupled oscillator 28, a power amplifier 29, and an antenna system 30, 3 I, all according to conventional practice. The output circuit of the pedestal generator I4 is coupled to the video-frequency amplifier 25, while the output circuit of the combining network I9 is coupled to the video-frequency amplifier 26.

Neglecting for the moment the details of the synchronizing signal-generating apparatus which embodies the present invention, the system just described comprises a television transmitting system of conventional design and the various parts thereof, illustrated schematically, being of wellknown construction, a detailed description of the o general system and its operation is unnecessary.

Briefly, however, the image of a scene to be transmitted is focused on the target of the cathoderay tube of the signal generator Ill, in which tube a cathode ray is developed, focused, and accelerated toward the target in the usual manner. Scanning or deflecting currents or voltages developed by the generators II and I2 are applied to the scanning elements of the generator I0 to provide electric fields which serve to deflect the cathode ray horizontally and vertically, thereby to scan successive series of parallel lines or fields upon the target. The deecting currents or voltages and, hence, the scanning elds are of wellknown saw-tooth form providing a relatively slow linear trace and rapid retrace. The number of lines per field are determined by the relative fieldscanning and line-scanning frequencies and these frequencies are preferably such, for example, 26,460 kilocycles and 60 cycles, respectively, that the successive fields are staggered or interlaced in the well-known manner. Block-out impulses developed by the generator I3 are applied to a control electrode of the cathode-ray tube to suppress or block-out the beam during retrace portions of the scanning cycles, while pedestal impulses developed by the generator I4 are applied to the amplifier 25 to suppress surges developed during the retrace period and to modify the resultant video-frequency wave developed, thereby to aid in the separation of line-synchronizing and frame-synchronizing impulses at the receiver.

The synchronizing impulses developed by the generators I6-I8, inclusive, are combined inA thc network I9 and applied therefrom as a composite synchronizing signal to the modulation amplifier 26. 'Timing impulses developed by the generator 22 are applied to the generators I I-I4, inclusive, and Iii-I8, inclusive, and to the control circuits 20, 2| to lock these generators in synchronism.

4The photosensitive elements of the target in the cathode-ray tube generator 'I0 being electrically affected to an extent depending upon the varying values oi. light and shade at incremental areas of the images focused thereon as the cathode-ray scans the target, a videofrequency voltage 4of correspondingly varying amplitude is developed in the output circuit of the generator I 0 and applied to the video-frequency amplifier 24, wherein this voltage is amplied and from which it is translated to the amplifier 25. Here the video-frequency .voltages are .further amplified and mixed with the pedestal impulses supplied from the generator I4. The mixed amplified voltages in the output circuit of the amplifier are thereupon applied to the amplifier 26, wherein they are further amplified and mixed with the composite synchronizing signal supplied from the combining network I9. The composite modulation signal is then supplied to the modulator 21, wherein it is impressed upon the carrier wave generated by the oscillator 28, and the resultant modulated-carrier signal is delivered to the power amplifier 29 for amplification and is thereafter impressed upon the antenna system 30, 3I to be broadcast.

Referring now more particularly to the apparatus embodying the present invention and the circuits associated therewith, the composite synchronizing signal-generating apparatus I5 includes, as stated above, the line-synchronizing impulse wave generator I6, the alternate-impulse Y wave generator I1, and the parabolic-impulse wave generator I8. The generator I6 includes energy-storage means, such as axcondenser 32, having a resistor 33 in series therewith, the latter having an impedance which is relatively very small compared to that of the condenser 32 at the oscillation frequency. A charging circuit is provided for the condenser 32 which includes a source of direct current, for example, a battery 34, preferably grounded at its negative terminal, a resistor 35 and thespace current path of a vacuum tube 36. A discharging circuit comprising an adjustable resistor 31 is connected across the condenser 32. The tube 36 serves as means for controlling the charging and discharging circuits to effect periodic charging and discharging of the condenser 32. There is also provided regenerating tube 38 having its cathode grounded and its anode connected to the control electrode of the tube 36, while the control grid of the regenerating tube is connected by way of a suitable coupling condenser 39 to the anode of the tube 36.- A buffer amplifier tube 40 is preferably interposed between the generator, per se, and the timing-impulse generator 22 to which it is coupled by way of a suitable condenser 4I to receive synchronizing or control impulses of twice the line-scanning frequency. A suitable grid-leak resistor 42 is connected between the control grid and cathode of the tube 40, while operatingI potentials vmay be supplied to the anodes of the tubes 38 and 49 from a battery 43 by way of a common load resistor 44. A leak resistor 45 is connected to the grid of the regenerating tube 38 and is utilized in accordance with the'present invention, as will be presently explained. The alternate-impulse wave generator I'I is of the same construction and operation as the generator I6, similar elements being designated by the same reference numerals with theV suffix a.

For the purpose of controlling the operation of each of the generators I6, I1 in accordance with the operation of the other, or more particularly to disable one of the charging or discharging circuits of one of these generators during the operation of the corresponding circuit of the other generator, there is provided a direct connection 46, including resistor 45a, between the control grid of the regenerating tube 38a of the generator I1 and the high potential terminal of the resistor 33 of the generator I6. If desired, a similar additional connection 41, including resistor 45, may be provided between the control grid of the regenerating tube 38 of generator I8 and the high potential terminal of-the resistor 33a of generator I1.

The combining network I9 preferably comprises three high impedance pentode amplifier tubes 48, 49, and 50. The output circuits, including the leads 46a and 41a, of the generators I6 and I1 are connected to the control grids of the tubes 50 and 49, respectively, while the output circuit of the parabolic-impulse generator I8 is connected to the control grid of the tube 48,. The

anode circuits of these tubes are connected in l paralleland coupled to the amplifier 26 by way of a coupling condenser 6I Operating potentials are supplied to the anodes of the tubes by way of load resistor 52 and choke 53 and to the screens from suitable sources indicated generally at +B and-i-Sc. 'I'he suppressor grids of the tubes 48 and 49 are normally biased sufficiently negatively to maintain these tubes nonconductive, as by means of batteries 54 and leak resistors 55. The suppressor grids of the tubes 48 and 49, however, are also coupled to the control circuits 20 and 2 I, respectively, each of which comprises suitable Letters Patent No. 2,052,184, granted August 25,.

1936, upon the application of Harold M. Lewis, generating periodic-impulse waves of line-scanning frequency in a manner well understood in the art, so that a detailed explanation thereof is unnecessary. Briey, however, in generator I6, the condenesr 32 is rapidly charged from the source 34 by way of the tube 36 and is discharged at a relatively slow rate through the resistor 31. The discharging action continues until the potential diference developed across the tube 36 is sufdcient, upon the application of a synchronizing impulse to its control grid from the generator 22, to break down the tube 36 and initiate another charging action. The initial surge of charging current results in a voltage impulse across the resistor 35 which is impressed negatively by way of condenser 39 upon the control grid offthe regenerating tube 38, reducing its conductivity. A positive impulse peak is thereby developed across the load resistor 44 and applied to the control grid of the tube 36 to accelerate or regenerate its charging action. The synchronizing or timing impulses from the generator 22 are applied to the control grid of the tube 36 by way of the condenser 4I and the buffer amplifier 40 and serve to synchronize the operation of the generator at the line-scanning frequency.

The periodic charging and discharging ofv the condenser 32 causes a voltage to be developed thereacross which has a saw-tooth wave form and, hence, a current flows through the condenser 32 and resistor 33 which has a periodic rectangular-impulse wave form, that is, a wave form which is the rst derivative' of the sawtooth voltage wave form. 'Ihis voltage is impressed upon tube 50 of the combining network auV I 8 by way of the leads 46 and 46a. Similarly, the generator II developsva voltage across the resistor 33a which is applied by way of the leads 4l and 41a to tube 48 of the combining network. The natural frequencies of the generators I3 and l1, that is, the frequency at which they would operate without synchronizing control, are slightly lower than the desired line-synchronizing frequency to ensure operation at half the applied synchronizing frequency, the latter being double the line frequency.

Assuming a point in the cycle when the tube 36 is passing current to charge its condenser 32, the current is then flowing through the resistor 35 in its anode circuit biasing the control grid of the reversing tube 38 negatively, which is the proper direction to effect the regenerative action, while the current is flowing through resistor 33 in series with the condenser 32 in such direction as to develop thereacross a positive voltage which is applied to the control grid of the reversing tube 38a. This positive voltage is in the proper sense to cause the reversing tube 38a to block the tube 36a, that is, it is opposite to that required for regeneration of generator II so that the initiation of the next cycle of this generator is prevented. Similarly, the voltage developed across the resistor 33a during charging of condenser 32a of the generator Il is applied to the control grid of the regenerating tube 38 of the generator I6 to prevent the initiation of the next cycle of this generator during charging of generator I'I. That is, the charging circuit of each generator is disabled during the charging operation of the other generator. Obviously, therefore, the two generators, while having a synchronizing-impulse wave from generator 22 applied thereto which is of double the frequencies developed thereby, are selectively synchronized by successive impulses of this wave. In other words, the predetermined phase displacement between the impulses of the waves developed by the two generators is maintained.

The general operation oi' the system may be explained with reference to the curves oi.' Figs. 2-7, inclusive, which show the wave forms of the voltages or currents developed at various points in the system. Fig. 2 represents the signal appearing at the output circuit of the video-frequency amplier 25, video-frequency impulses indicated at V having been supplied from the cathode-ray signal generator I0 and line-frequency and frame-frequency pedestals p1 and pr having been determined or formed by voltage from generator I4 mixed with the video-frequency signal in the amplifier 25. The curve of Fig. 3 represents the double line-frequency synchronizingimpulse wave developed in one of the output circuits of the timing generator 22 and applied to the input circuits of the generators I6, Il, and I8. The curve of Fig. 4 represents the line-synchronizing impulse wave developed by the generator I6 and applied to the input circuit of the tube 58, while the curves of Figs. 5 and 6 represent the alternate line-frequency impulse wave and parabolic-impulse wave, the latter being at the double-line frequency developed by the generators Il and I8 and applied to the input circuits of the tubes 49 and 48, respectively. As explained above, alternate-line impulses occur intermediate the line-scanning impulses, while the parabolic impulses occur between the succeeding impulses' of the combined line-synchronizing impulse and alternate-impulse waves.

The final desired modulation signal developed by the system is of the wave form shown in Fig. 7, including the video-frequency voltages as well as the composite synchronizing signal. To develop such a wave, the line-synchronizing impulses are repeated continuously by the tube 6l. its operating voltages being such as to eifect this operation, while the alternate impulses are added during a part of the retrace portion of each fieldfrequency cycle, this portion corresponding to the duration of the field-frequency pedestal. During a part ofthe line-doubling period, the parabolic impulses are added or inserted 'between the line-synchronizing and alternate impulses to provide, in efi'ect, relatively long serrated ileld-synchronizing impulses for each ield cycle without interruption of the line-synchronizing impulses. The combined synchronizing signal is then combined with the video signal, as stated above, in the amplier 28.

The line-doubling and inserting operations are effected at the proper times and for the proper durations by virtue of the actions of tubes 48 and 49, controlled by their respective control circuits 20 and 2|. More particularly, since these two tubes are normally biased beyond cutoff by the suppressor bias batteries 64, they are normally nonconductive and the alternate and parabolic Waves do not appear in the common output circuit of the network I9. The positive control impulses which are supplied by the circuits 20 and 2 I, however, serve to unblock these tubes for predetermined periods at the field-scanning frequency, thereby to eil'ect the combining actions, as described above.

In Figs. 2 and 7 the points :n and z' correspond to the beginning and termination, respectively, of the frame-pedestal impulses, such as are supplied by the generator I4. 'I he line doubling, or addition of alternate impulses, takes place during the time interval between the points indicated at y and y in Fig. 7, the initiation of this action being preferably delayed for the period represented at d1. The addition 0r insertion of the parabolic impulses takes place between the points z and z', the initiation of this action being delayed for a period represented as dz. The control circuits 20 and 2l include suitable apparatus for effecting the required delays and durations of the control impulses.

The output circuits of the tubes", 4 9, and 80 being connected in parallel, when these tubes are conductive the signals impressed on their input circuits are combined in their common output circuit, the tube 50 continuously repeating the line-synchronizing impulses (Fig. 4) received from the generator I6 and the tubes 4l and 48 operating intermittently, as described above. The combined synchronizing signal is thus developed in the output circuit of the combining network I9, supplied to the ampliner 26, and therein mixed with the video-frequency signal, the resultant modulation signal of the desired wave form shown in Fig. 7 being thus obtained.

While therehas beendescribed what is at present considered to be the preferred embodi- -ment of this invention, it will be obviousto those ing a generator for generating a rst periodic wave of a predetermined frequency, a separate generator for independently generating a second periodic wave of said predetermined frequency, a synchronizing circuit adapted for the reception of a synchronizing wave of double said predetermined frequency and coupled directly to each of said generators for synchronizing their respective operations, and means for ensuring selective synchronization of said two generators by successive cycles of said synchronizing wave comprising a direct connection between said generators for controlling the operation of one in accordance with the operation of the other.

2. 'A periodic wave-generating system, comprising a generator for generating a first periodic Wave of a predetermined frequency, a separate generator for independently generating a second periodic wave of said predetermined frequency, each of said generators comprising energy-storage means, charging and discharging circuits for said storage means, and a control circuit for controlling said charging and discharging lcircuits to effect periodic charging and discharging or said storage means, and means for coupling the control circuit of one of said generators to one of the charging and discharging circuits of the other of said generators for disabling the corresponding circuit of said one of said generators during operation of said corresponding circuit of the other of said generators.

3. A periodic wave-generating system, comprising means for generating a rst periodic Wave of a predetermined frequency, means for generating a second periodic wave of said predetermined frequency, each of said generating means comprising energy-storage means, chargand discharging circuits for said storage means and means for controlling said circuits to eiect periodic charging and discharging of said storage means, and means coupling said generating means to prevent charging of the storage means of one of said generating means during charging of the storage means of the other of said generating means.

4. A periodic wave-generating system, comprising means for generating a rst periodic wave of \a\ predetermined frequency, means for generating a second periodic wave of said predetermined frequency, a synchronizing circuit adapted for the reception of a synchronizing wave of double said predetermined frequency and coupled to said generating means for synchronizing their respective operations, each of said generating means comprising energy-storage means, charging and discharging circuits for said storage means, and means for controlling said circuits to eiect a periodic charge and discharge of said capacitance means, and means for ensuring selective synchronization of said two generating means by successive cycles of said synchronizing Wave comprising means coupling said generating means to prevent charging of the storage means of one of said generating means during charging of the storage means of the other of said generating means.

5. A periodic wave-generating system, comprising means for generating a first periodic wave of a predetermined frequency, means for generating a second periodic wave of said predetermined frequency, each of said generating means comprising energy-storage means, charging and discharging circuits for said storage means, means for controlling said circuits to effect a periodic charge and discharge of said storage means and means for regenerating the action of said control means, and means coupling the charging circuit of one of said generating means to the regenerating means of the other of said generating means to prevent charging of the storage 4means of said other generating means during charging of the storage means of said one of said generating means.

6. A periodic voltage-generating system, comprising means for generating a rst periodic wave of a predeterminedA frequency, means for generating a second periodic wave of said predetermined frequency, each of said generating means comprising energy-storage means, charging and discharging circuits for said storage means, and a vacuum tube included in said charging circuit for effecting periodic charging and discharging cf said storage means, an impedance element in series with said tube in the charging circuit of one of said generating means, and means connecting a control element of the other of said generating means across said impedance element for preventing charging of the storage means of said other generating means during charging of the storage means of said one generating means.

7. A periodic voltage-generating system, comprising means for generating a first periodicimpulse wave of a predetermined frequency, means for generating a second periodic-impulse wave of said predetermined frequency, each of said generating means comprising energy-storage means, charging and discharging circuits for said storage means, and a vacuum tube included in said charging circuit for effecting periodic charging and discharging of said storage means, a synchronizing circuit adapted for the reception of a synchronizing-impulse wave of double said predetermined frequency and coupled to said generating means for synchronizing the respective operations, and means for ensuring selective synchronization of said two generating means by successive impulses of said synchronizing wave, comprisingan impedance element in series with the tube in the charging circuit of one of said generating means, and means connecting a control element of the other of said generating means across said impedance element for preventing charging of the storage means of said other generating means during charging of the storage means of said one generating means.

8. A periodic voltage-generating system, comprising means for generating a iirst periodic wave `of a predetermined frequency, means for generating a second periodic wave of said predetermined frequency, each of said generating means comprising energy-storage means, charging and discharging circuits for said storage means, and a vacuum tube included in said charging circuit for effecting periodic charging and discharging of said storage means, means coupled to said tube for regenerating the action thereof, and means coupling the charging circuit of one of said generating means to the regenerating means of the other of said generating means for preventing charging of the storage means of said other generating means during charging of the storage means of said one generating means.

9. A periodic voltage-generating system, comprising means for generating a rst periodic-impulse wave of a predetermined frequency, means for generating a second periodic-impulse Wave of said predetermined frequency, each of said generating means comprising capacitance means, charging and discharging circuits for said capacitance means, and a vacuum tube included in eration thereof by successive synchronizing impulses, and means coupling the charging circuit of one of said generating means to the regenerating means of the other of said generating means for preventing charging of the capacitance means of said other' generating means during 5 charging oi the capacitance means of said one generating means.

HAROLD M. LEWIS.