US2459699A - Synchronizing system - Google Patents

Description

Jan. 1s, 1,949.

c, E. HALLMARK SYNCHRONIZING SYSTEM Filed Feb. 1, 1946 2 Sheets-Sheet l .Da DO JON-.P200

INVENTOR GLYDE E. HALLMARK .0mm 2 ON u .0mm 2 ON L m ATTORNEY c. E. HALLMARK SYNCHRONIZING SYSTEM Jan. 18, 1949.

'Filed Feb. 1, 1946 2 Sheets-'Sheet ou d lNvENToR CLYDE E. HALLMARK @Lily ATTORNEY Patented Jan. 1s, 1949 SYNCHRONIZING SYSTEM Clyde Edwin Hallmark, lFort Wayne, as-

vsignor, by mesne assignments, to Farnsworth Research Corporation, a corporation of Indiana Application February 1, 1946, serial No. 644,872

This invention relates to synchronizing systems, and particularly relates to a method of and system for synchronizing' a low frequency wave generator and a high frequency wave generator. The problem frequently arises of synchronizing two harmonically related wave generators. Inv

`11 claims. (o1. 25o-36) vthe television art, for example, it is necessary for the proper reproduction of the television imageV to interlock with respect to time the field frequency wave of 60 cycles per second with a wave rof 31,500 cycles per second, corresponding to twice the line frequency. Present television standards require the transmission of 60 fields Vper second and 525 lines per frame, each frame comprising two fields. Accordingly, the line frequency is l5,'750-cycles per second. In television systems, synchronization is further complicated byV the fact that a lowfrequency generator is usually coupled to the 60 cycle power line and,

therefore, follows the variations in frequency of the power line. v

A conventional synchronizing system suggested for this purpose employs frequency dividers for stepping down `the frequency of thehigh frequency wave to that of the low frequency wave.

The two Waves of substantially equal frequency are then compared in phase toderive a signal which may be utilized for controlling one of the y two wave generators. A system of this type suffers from the drawback that a chain of frequency dividers,.suchl as multivibrators, is required for reducing the frequency of the high frequency wave to that of the low frequency wave. Another synchronizing system has been proposed where the low frequency and high frequency waves are compared directly. To this end, a pulse, which .is narrow in comparison .with a half cycle of the high frequency wave, is derived from the low frequency sinusoidal wave. The narrow pulse is superimposed on the high frequency sinusoidalv wave and rectied to derive a control signal for controlling the frequency of the high frequency wave generator. This system has the drawback that extremely narrow pulses must be developed from a low frequency sinusoidal wave. These narrow pulses cannot be used for any other purpose, while the high frequency sinusoidal wave -must then be shaped to derive high frequency pulses which are required for the synchronizing signal of a television system.

It is an object of the present invention, therefore, to provide a n ovel synchronizing system which will overcome the above mentioned drawbacks of prior systems and which will be comparatively simple in construction and reliable in operation.

A further object of the invention is to provide a method of and system for synchronizing a low frequency wave generator and a high frequency l wave generator harmonically related thereto Inaccordancewith the present invention, there p is provided a synchronizing system comprising means for developing low frequency pulses substantially ata frequency f and means for developing high frequency pulsesl substantially at ,a

frequency nf, Vwhere n is an integer. Means are provided for selecting groupsof the high frequency pulses at recurring time intervalsk equal to the reciprocal lof the frequency f. Means are furtherprovided for developing a pedestal wave having the same'frequency asthe low frequency pulses and meansfor mixing the selected groups of high frequency pulses with the pedestal wave. Thus a frequency control signal isv derived. Finally means are provided for.r controlling the frequency of one of the pulses in accordance with the frequency control signal. In this manner the high frequency pulses are synchronized with the low frequency pulses. v y v For a better understanding of the invention, together with other and further. objects thereof, reference is made to the following description rtaken*r in connection with the accompanying drawings, and its scope will be pointed out in the appended claims. y,

In the accompanying drawings, Fig. 1 is a block diagram of a synchronizingsystem embodying A,input wave of the frequency ,f may be obtained. Accordingly, generator I will follow the average or slow variations in frequency of the input wave obtained from lead 2. The sinusoidal wave developed by low frequency generator I, as illustrated att, is Apassed through pulse Shaper i4 `where pulses 5 at the frequency f are developed. Pul'ses 5 preferably have a width of vthe order of 20 microseconds.l

There is further yprovided a highrfrequency sinusoidalfwave. generator 6 which develops a sinusoidal wave indicated at 'I at thefrequency nf, where n may, for example, be equal to 525 sov that the requency nf equals 31,500v cycles per second. High frequency sinusoidal wave 1 is passed through pulse shaper vnto. develop high frequency pulses at the frequency nf indicatedy at It'l.l Highfrequency pulses I0 preferably have a width of the orderof 5 microseconds.

Fig. 1, there is illustrated av In accordance with the present invention every nth pulse ,ofhi'gh frequency pulses-II!4` is selected to derive pulses at the Jfrequency f. This is accomplished by keyed amplifier II connected to the output of pulse shapers 4 and 8. Keyed amplier II is arranged to be rendered operative whenever a low frequency pulse 5 is impressed thereon. During that time; aghi-gh A.frequency pulse I is amplified. Thuslkeyed'amplierfIFIL is" rendered operative at recurring time intervals equal to the reciprocal of the frequency f-Which is y 1/eo second in the lpresent example. Output wave I2 of keyed amplier I ,I accordingly consists-of f pulses having a time duration of approximately microseconds and recurring, at the 'frequency f. An output signal-consisting o'f pulses'at thefrequency flmay be derived from lead I3- connected to the output of keyed amplifier I I, While an output signal consisting' of vpulses recurring at the frequency nf may be obtained from lead I4 connected to 'the output of` pulse shaper. The pulses obtained from output leadsIB'and I4, therefore, vhave a 'time duration of yapproximately 5"microse'cor-idsfr The pulses derived from outputl leads I3 and I4fmayvbe utilized, for example, lfor developingy synchronizing or blanking signals of the type required in a television system.

For the purpose of comparing the phases of the waves developed by generators I and 6, wave having a sloping portion is derived from low frequency pulses 5 bymeans of saw-tooth Wave shaper I5". Wave I6 'developed by Wave shaper I5-may be of triangular or saw-tooth shape, as'illustrated, or itmay have any Wave form comprising a sloping portion *suchV as a sinusoidal wave or'a symmetrical saw-tooth wave. Saw-tooth wave I6 preferably has a ytime durationy which'eqfuals that of low frequency pulses 5. that is, a time duration of approximately `2O microseconds.

By means of mixerf'll connected to the output of keyed amplifier I'I andof 'saw-tooth Wave shaper I5, narrow'pulses I2v are set on the sloping vportion of'saw-tooth wave IS as illustratedat i8.

Thus saw-tooth wave 'ILS serves as 'a pedestal for pulses I2. Depending on the phase relationship between pulses I2 derived from'high frequency generator .5, and saw-tooth wave I B derived from low frequencyv generatorjl, the position ofpulses I2 `Will vary with respect to saw-tooth wave I6. In other words, the height of pulses I2 will vary With respect to a referencepotential depending uponthephase relationship between low frequency wave 3 and high frequency wave 1. 'However, the height of pulses I2`of wave I3 Willonly then be an indication of this phase relationship when pedestal wave I6 has a sloping portion. Wave I8 is rectified and may be amplified by rectifier and VDQ C. amplifier 2U to vderive r an amplified output signal which is representative of this phase relationship. The frequencycontrol signal developed by D. C. amplier 20 may be passed through'low pass filter 2l Where the `alternating,'current .components of the control signal areremoved. The filtered frequency con- .trolsignal may be: used for controlling automatic frequency control circuit 22 which in turn controls thefrequency-of high frequency generator 6 in a conventional manner.

.As stated previously, the time duration of loW frequency pulses k5 aswell as that of saw-tooth wavelB may be betweenZOto 30 microseconds,

that is, of-.the ordercf `one cycle of the high fre.- quency wave.v Since high frequency pulses I2 It is also feasible to select a plurality of pulses instead ofv one pulse each time keyed amplifier I I lis rendered voperative by the arrival of a 10W frequency pulse 5. AAllthat is necessary is to make low vfrequencyy pulses 5 slightly broader or of larger time duration so that keyed amplifier I I is rendered operative for. a length of time suillcient to pass a plurality of pulses instead of one. Saw-tooth` wave I6 preferably should have substantially the same width as low frequency pulses 5. Accordingly a group of pulses mghtfbeiselt; on the sloping portion offsaW-.tooth wave Iinstead of one pulse. Howeven'tlfie,synchronizingsysg tem of the invention -will :be more sensitiveito `changes in phase when 'low frequency pulses 5 are sufficiently narrow to .select-'one of high fre.- quency pulses Eil rather than .a plurality thereof every timefkeyed -amplier ,-,H is renderedoperative., x y

Referring now to Fig. -2, thereis illustratedthe synchronizing system, ofA Fig. v1 ingreater detail. The circuit of Fig. 2 isseparated by dotted lines into' componentqparts which are designatedfby the same reference numerals asxwere used in Eig. s vl to facilitateidentification of the circuit. -LQW frequency sinusoidal wave generatorfl is ofthe resistor capacitor o or ,RC -.type. RC oscill-ator -I comprises triode Zhaving its-. grid coupled to the anode through delay network 26. Delay network 2 6 comprises' 'three sections. each .includingga '-.series condenser 2l and a shunt `resistor l28.

Shunt resistor 30;ar'ranged :in series with-resistor `S'i-.is adjustablesfor manual control of thephase delayintroduced by network 26'. `Triode 25- will oscillate at the frequency^for-which network 2 6 introduces a phase shiftof #degrees For-the circuit constants of delay-network l26 shownz'in v Fi'g..2, triode 2,5 willv developa sinusoidal/'Wavelet a frequency of 60 cycles.

The anode voltage maybe supplied Y'toltlie anode ofk triode` 25 vfrom l,voltage source" 28 through low pass filter 32. Input lead 2, .which `maybe connected tothe power line',supplies a 60;'cycle` sinusoidal wave and is floos'ely coupled coupled through coupling condenser 34 to the cathode ofgtriode `35-arranged as a diode :rectifier. The input signal is coupled' across cathode resistor 56 of rectifier 35, and the rectified output signal is developed-across anode resistor 31. The output signal of rectifier 35consists ofl avrectied sinusoidalhalf -wave goty negative polarity asA indicated-at. 38." sinusoidal half-Wave 3.8; is cut ,01T or clipped by clipperf, the outputsignal-developed across anode-resistor` Ill being shown atlI2.' .f -f

Square-topped wave 'S42 is passed through differentiating'network 43 which comprisesa-series condenser and a'shunt resistorl and is' coupled to the grid voftrode AIL-negatively 'biased' through potentiometer 45. The wave developedbydif-f ferentiating network :43 -is indicated at-,46 and includesY comparatively sharp peaks. Triode M .is arranged as a clipper tube which clips off the sharp Ipeaksfof wave-56.. The output signal -of clipper 44 is developed across anode resistor 41 and indicated at 48. Wave 48 consists of pulses v of negative polarity, each having a time duration of 300 microseconds. Output pulse 48 is again passed through a differentiating network 50 Where the pulses are narrowed. Differentiating network 50 is connected to the grid of clipper tube 5I. The grid of clipper tube 5I is negatively biased by potentiometer 52. Output pulse 53 developed across anode resistor 49 is similar in shape to output pulse 48 but has a width of 20 microseconds only.

Outputpulse 53 is amplified by tube sections 54 and 55 arranged in a common envelope in the manner of a duplex tube. The anode of tube section 54 is coupled to the grid of tube section 55 arranged as a cathode follower. Amplified output signal 56 of positive polarity is developed across cathode resistor 51 of tube section 55. Output signal 56 has a time duration of 20 microseconds and consists of pulses of positive polarity having a peak-to-peak voltage of 160 volts and recurring at a frequency of 60 cycles per second.

High frequency sinusoidal wave generator 6 also is arranged as an oscillator of the RC type. Rc oscillator 6 includes pentode 80 having its control grid coupled to the anode through delay network 6I comprising four sections, each consisting of a series condenser 62 and a shunt resistor 63. Resistor 64 is adjustable for manual control of the frequency or oscillator 6. Automatic frequency control tube 65 acts as a variable shunt resistor of one section of delay network 6I. Delay network 6I is designed to introduce a 180 degree phase shift between the control grid and the anode of pentode 69 at a frequency of 31,500 cycles per second. By varying the resistance of automatic frequency control tube 65, the frequency developed by oscillator Ii may be varied. The plate voltage of pentode 60 is supplied through low pass filter 66. The suppressor grid of pentode 60 is connected to ground, as is conventional, while the screen grid is supplied with a suitable positive voltage through resistor 61.

The sinusoidal wave developed by high frequency generator 6 at the frequency of 31,500 cycles per second is derived from the plate of pentode 60 and is connected to pulse shaper 8 which has been shown in block form to avoid confusion. Pulse shaper 8 may be similar to pulse shaper 4 and should be arranged to develop output pulses at a frequency of 31,500 cycles per second, each pulse having a time duration of approximately 5 microseconds. Output pulses at a frequency of 31,500 cycles per second may -be obtained from output lead I4 connected tothe output of pulse Shaper 8.

The output of pulse Shaper 8 is also connected to the control grid of pentode 1i! which isarranged as a keyed amplifier. The cathode and the suppressor grid of pentode are both connected to ground. The screen grid of pentode 16 is connected to ground through resistor 1I so that it is normally at ground potential thus rendering pentode 10 inoperative. Output pulses 56 developed by pulse shaper l are supplied to the screen grid of pentode 10 through coupling condenser 12. Exery time a pulse 56 of positive polarity is impressed upon the screen grid of pentode 15, its potential is sufficiently raised to render pentode 10 operative for the time duration of pulse 56. During that time a pulse or a plurality of pulses, as the case may be, developed by pulse Shaper 8 is amplified by keyed amplifier 10.

6 AThe output signal is developed across anode resistor 13 and fed to mixer I1. An output signal consisting of pulses, each having a time duration of approximately 5 microseconds, and having a frequency of 60 cycles per second may be obtained through output lead I3.

Output pulses 56 developed by pulse shaper 4 are further shaped in saw-tooth wavel Shaper I5 to derive a saw-tooth Wave. Shaper I5 comprises differentiating network 15 where pulses 56 are differentiated to develop a `wave indicated at 16 which is clipped by clipper 11 having a suitable grid bias battery 18. The clipped wavewhich is of saw-tooth or triangular wave form as indicated at 80 is supplied to mixer Il as is the output signal of keyed amplifier 16. Saw-tooth wave 80 has substantially the same width as pulses 56, that is, a time duration of approximately 20 microseconds. In mixer i1 the narrow 60 cycle pulses derived from keyed amplifier 10 are set on triangular wave SIB as shown at I8 in Fig. 1.

The output signal or mixer I1 is rectified and amplified by rectifier and D. C. amplier v2li and passed through low pass filter 2i which is arranged to remove the alternating current component of the signal.v The rectified and filtered frequency control signal is supplied to the control grid of automatic frequency Icontrol tube 65. Accordingly, a control signal of Variable voltage depending upon the phase' difference of the pulses developed by pulse Shapers 4 and 8 is impressed upon the control grid of tube 65, thus varying its resistance. Automatic frequency control tube acts as a variable resistor of one section of delay network 5i thereby to control the frequency of pentode oscillatorr Silv in accordance with the control signal.

While it will be understood that the circuit specifications of the synchronizing system of the invention may vary according to the design for any particular application, the: values of the circuit constants of the synchronizing circuit of Fig. 2 are shown in the drawings, by way of example only, as suitable for developing pulses at frequencies of 60 cycles per second and of 31,500 cycles per second, respectively. The tubes shown in Fig. 2 preferably are of the following types:

Triodes 25, 35, 40, 44 and 51- 1/2Type Gsm- GT Pentodes 60 and 70 Type 6AC'1 Triode 65 l/zrype esNv-GT While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l.. A synchronizing system comprisingfmeans for developing low frequency pulses-substantially at a frequency f, means for developing high frequency pulses substantially Aat a frequency nf, where n is an integer, means rendered operative only by said low frequency pulses for selecting groups of said high frequency pulsesr at recurn y quen cy a frequency control ring time intervals equal to the reciprocal of said frequency means for shaping said low frequency pulses to develop a pedestal wave having the same frequency as said low frequency pulses, means for mixing said selected groups of high frepulses with said pedestal wave to derive signal, and means for controlling: the frequency of one of said pulses in accordance with said frequency control signal.

2.: AV synchronizing system comprising means for ydeveloping low` frequency pulses substantially ata frequency f, means for developing high frequency pulses substantially at a frequency nf, Where n is an integer, said low frequency pulses having each a duration of the'order of the reciprocal of said high frequency, a keyed amplier rendered operative only by said low frequency pulses for selecting groups of said high frequency pulses? at recurring time intervals equal to the reciprocal of said frequency f, means for shaping said low frequency pulses to develop a Wave having; a sloping portion and having the same frequencyv and substantially the same duration as said low frequency pulsesfmeans for superimposin'g said selected groups of high frequency pulses upon said sloping wave portions to derive a frequency control signal, and means for controlling the frequency of said high frequency pulses in accordance with said frequency control signal.

3. A synchronizing system comprising a rst oscillator` for developing a low frequency sinusoidal-Wave substantially at a frequency f, a power line for supplying a sinusoidal wave substantially atsaid frequency f, said power line being loosely coupled to said first oscillator, means for deriving low frequency pulses from said low frequency sinusoidal wave, said low frequency pulses having the' samey frequency as said loW frequency wave, a second oscillator for developing a high frequency sinusoidal wave substantially at a frequency nf, Where n is an integer, said low frequency pulses having each a duration of the order of the reciprocal of said high frequency, means for deriving high frequency pulses from said high frequency sinusoidal wave, said high frequency pulses having the same frequency as said high frequency wave, means controlled only by said low frequency pulses for selecting groups of said high frequencyA pulses at recurring time intervals equal to the reciprocal of said frequency f, means for shaping said low frequency pulses to derive a Wave having a sloping portion and substantially the same duration as that of said loW frequency pulses, means for superimposing said selected groups of high frequency pulses upon said sloping wave portions to derive a frequency control signal, and means for controlling said second oscillator in accordance with said frequency control signal.

4. A synchronizing system comprising means for'developing loW frequency `pulses substantially at a frequency f, means for developing high frequency pulses substantially at a frequency nf, where n is an integer, said low frequency pulses having each a duration of the order of the reciproca] of said high frequency, means rendered operative only by said loW frequency pulses for selecting every nth of said high frequency pulses, means for shaping said lowv frequencyA pulses to develop a Wave having a sloping portion and having the same frequency and substantially the same duration as said low` frequency pulses, means for mixing said selected high frequency pulses With said sloping wave to derive a fre,

quencyy control signal, and means for controlling the frequency of one of said pulses in accordance lwith said frequency control signal.

5. A synchronizing system comprising means for developing low frequency pulses substantially at a frequency f, means for developing high frequency pulses substantially at a frequency nf,

8 where nis anl integer, said low frequency pulses having each a time durationvof morer than 2M a keyed amplifier controlled by said lowfrequency pulses for selecting every nth of said high frequency pulses, means for shaping said low fre.- quency pulses to derive awave having a sloping portion and substantially the same duration as that of said low frequency pulses, means` for superimposing said selected high frequency pulses upon said sloping wave portions to derive a composite wave, means for rectifying and filtering said composite `wave to derive a frequency control signal, andmeans for controlling the frequency of one of said pulses rin accordance with said frequency control signal. y

6. A synchronizing. system comprising means for developing a low frequency sinusoidal wave substantially at a frequency f, means for deriving low frequency pulses from said low frequency sinusoidal wave, said low frequency pulses having the same frequency as said low frequency wave, means for developing a high frequency sinusoidal wave substantially at a frequency nf, where n is aninteger, means for deriving high frequency pulses from said high frequency sinusoidal Wave, said high frequency pulses` having the samefrequencyl asv said high frequency wave, said. low frequency pulses having each a time duration of the order of one cycle of said high frequency sinusoidal wave, a keyed amplier rendered operative by said low frequency pulses .for selecting every nth of said high frequency pulses, means for shaping said low frequency pulses to deriye a wave having a sloping portion and substantially the same duration as that of said low frequency pulses, means for setting said selected high frequency pulses upon said sloping wave portions to derive a frequency controlsignal, and means for controlling the frequency of one of said sinusoidal waves in accordance with said frequency con-ftrol signal.

7. A synchronizing system comprising a. low frequency oscillator for ydeveloping a low frequency sinusoidal Wave substantially atl a frequency f, a power line forsupplying a sinusoidal Wave substantially at said frequency said power line being loosely coupled to said low frequency oscillator, means for deriving low frequency pulses from said low frequency sinusoidal Wave, said low frequency pulses having the same frequency as said low frequency wave, a high frequency oscillator for developing a high frequency sinusoidal Wave substantially at a frequency nf, Where n is an integer, means for deriving high frequency pulses from said high` frequency sinusoidal Wave, said high frequency pulses having the same frequencyas said high frequency wave, said low frequency pulses having each a duration of the order of the reciprocal of said high frequency, means controlled by said low frequency Wave for selecting every nth of said high frequency pulses, means for shaping said loW frequency pulses to derive a wave having a sloping portion and, substantially the same duration. as that of said` low frequency pulses, means for superimposing said selected high frequency pulses upon ysaid sloping Wave portions to. derive 'afrequency control signal, and means for controlling said high frequencyv oscillator in accordance wit said frequency control signal.

v8. The method of synchronizingY two har'- monically related-Waves which comprises develop'- 1 and less than ing low frequency pulses substantially at a frequency j, developing high frequency pulses substantially at a frequency nf, where n is an integer, selecting groups of high frequency pulses at recuring time intervals equal to the reciprocal of said frequency f, shaping said low frequency pulses to develop a pedestal wave having sloping portions ofthe same frequency as said low fre-f quency pulses, said sloping wave portions having each a duration of the order of the reciprocal of said high frequency, mixing said selected groups of high frequency pulses with said pedestal Wave to derive a frequency control signal, and controlling the frequency of one of said pulses in accordance with said frequency control signal.

9. The method of synchronizing two harmonically related waves which comprises developing a low frequency sinusoidal wave substantially at a frequency f, developing a high frequency sinusoidal wave substantially at a frequency nf, where 1L is an integer, deriving high frequency pulses from said high frequency sinusoidal wave, said high frequency pulses having the same fre-- quency as said high frequency Wave, selecting groups of said high frequency pulses at recurring time intervals equal to the reciprocal of said frequency f, developing a wave having sloping portions and having the same frequency as said low frequency sinusoidal Wave, said sloping wave pore tions having each a duration of the order of the reciprocal of said high frequency, setting said selected groups of high frequency pulses upon said sloping wave portions to derive a frequency control signal, and controlling the frequency of one of said sinusoidal waves in accordance with said frequency control signal.

10. The method of synchronizing two harmonically related waves which comprises developing low frequency pulses substantially at a frequency f, developing high frequency pulses substantially at a frequency nf, where n is an integer, said low frequency pulses having each a duration of the order of the reciprocal of said high frequency, selecting every nth of said high frequency pulses, developing a wave having a sloping portion and having the same frequency and substantially the same duration as said W fre- 10 quency pulses, superimposing said selected high frequency pulses upon said sloping wave portions to derive a frequency control signal, and controlling the frequency of one of said pulses in accordance with said frequency control signal.

l1. The method of synchronizing two har-- monically related waves which comprises developing a low frequency sinusoidal Wave substantially at a frequency f, deriving low frequency pulses from said low frequency sinusoidal wave, said low frequency pulses having the same frequency as said low frequency wave, developing a high frequency sinusoidal wave substantially ata frequency nf, where n is an integer, deriving high frequency pulses from said high frequency sinusoidal wave, said high frequency pulses having the same frequency as said high frequency wave, said low frequency pulses having each a duration of the order of the reciprocal of said high frequency, selecting every nth of said high frequency pulses, shaping said low frequency pulses to derive a wave having a sloping portion and substantially the same duration as said low` frequency pulses, superimposing said selected high frequency pulses upon said sloping wave portions to derive a frequency control signal, and controlling the frequency of said high frequency sinusoidal wave in accordance with said frequency control signal.

CLYDE EDWIN HALLMARK.

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

Ser. No. 464,750, De France (A. P. C.), pub. June 8, 194B.

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