Sept. 17, 1946. 2,407,956 C. E. HALLMARK SYNCHRONIZING SIGNAL GENERATOR Filed NOV. 18, 1943 t0 mln 1. en mi .LA wvvll' Il l 1 mw\ ww, uti1l-4. INVENTOR ATTORNEY Patented Sept. 17, 1946 2,407,956 UNITED STATES PATENT OFFICE 2,407,956 SYNCHRONIZING SIGNAL GENERATOR Clyde E. Hallmark, Fort Wayne, Ind., assigner to Farnsworth Television andRadio Corporation, a corporation of Delaware Application November 18, 1943, Serial No. 510,759 4 Claims. (Cl. 178-7.2) 1 2 This invention relates :to frequency generators and particularly to scanning frequency gener ators for television systems. Where it is desired `to control the frequency of an oscillator automatically, it is customary to use a so-called LC type of oscillator for 4the rea son that a reactance tube may be employed as In television systems it is common practice to generate the scanning frequency voltages in such the frequency varying means. Howeverll it fre quently is desirable to use a Slo-called RC type of a manner that the frequencies of these voltages are maintained in a predetermined relationship oscillator but, a device of this character is not with a standardizing frequency. It generally is susceptible of automatic frequency control by convenient to utilize as the standardizing fre means of a conventional reactance tube. quency a 60 cycle alternating current derived 10 Another object of th'e invention is to provide a from a commercial power source. According to novel‘automatic frequency control for an RC type the present RMA standards video signals are of oscillation generator. transmitted at the rate of 30 frames per second. In accordance with the `present invention there Each frame comprises an odd number of scan is provideda means for producing oscillations of ning lines and, where a 2 to 1 interlaced Scanning a’distortedwave form at a submultiple frequency pattern is used, th'e field scanning frequency is of the standardizing source. The distorted wave 60 cycles per second. ` form contains a number of harmonics of the sub The scanning frequencies usually are derived multiple frequency, one of which is nominally from an oscillator which is operated either at a equal to Vthe frequency of the standardizing high or a low frequency. In the case of a low 20 source. This harmonic and the standardizing frequency oscillator its frequency ordinarily is frequency are compared'to develop an automatic 60 cycles per second and its output voltage is frequency control `voltage for employment in multiplied in frequency rto twice the line scan connection with the oscillator. ` ning frequency. Such an expedient is necessary The form :of oscillation generator utilized com for the reason that the line scanning frequency 25 prises a vacuum tube having the output and in for an odd number of scanning lines is not an put circuits thereof coupled by a phase shifting even harmonic of the 60 cycle oscillator fre network for the feedback of output circuit energy quency When a 2 to 1 interlaced scanning pattern to the input circuit. The network comprises a is used. 'I'he line scanning frequency is derived plurality of meshes, each including resistance from the voltage having twice the line scanning 30 and reactance of one type only. The resistance frequency by th'e use of a frequency divider. element of one of the phase shifting meshes con The 60 cycle frequency for the oscillator gener sists of the space discharge path of a vacuum ally is chosen for the reason that it conforms to tube. The `magnitude of this resistance element the ñeld scanning frequency and also to the fre is varied by the automatic frequency control Volt quency of the standardizing source. Numerous 35 age to vary the total phase shift of the feedback arrangements have been utilized for comparing energy and, thus, vary the frequency of oscilla the 60 cycle oscillator frequency with the 60 cycle tion. alternating current derived from a commercial For a better understanding of the invention, power source and for utilizing the output of the together »with other and Yfurther objects thereof, frequency comparator to control the oscillator 40 reference is had to the following description frequency so that it will be in agreement at all taken in connection with the accompanying times with the source of a standardizing fre drawing, and its scope will be pointed `out in quency. the appended claims. In an arrangement Wh'ere the oscillator is op In th'e drawing, the single figure isa schematic erated at a high frequency it also is necessary, 45 circuit diagram of a scanning frequency gener in order to derive the low frequency scanning ator and automatic frequency control apparatus voltages and a voltage suitable for Vcomparison embodying the invention. withthe standardizing source, to employ a num Having reference `now to the drawing, it is as ber of frequency dividers. sumed that `it is desired to generate scanning It is an object of the instant invention, there 50 voltages for a -televisionsystem employing an odd fore, to provide a novel means `for generatingtel number `of scanning lines per frame and 30 evision scanning voltages definitely` related `in frequency to a standardizing frequency and in >framespersecond with a 2 to 1 interlaced scan ning pattern. In such a case the frequency of which theuse Qf'frequency» dividing apparatus is obviated. 55 the field scanning 4voltage will be 60 cycles `per second. Also, in this case thesource of stand~ 3 2,407,956 4 ardizing frequency is assumed to be a conven tional 69 cycle source of commercial alternating current. In accordance with the invention then, the oscillation generator is arranged to de velop sinusoidal voltage at a sub-harmonic fre quency of the frame scanning Vfrequency of 60 cycles. For illustrative purposes the i'lrst sub harmonic of 30 cycles per second will be utilized. The oscillation generator comprises _a vacuum tube I which, in the present instance, is illus 10 trated as a pentode. However, it is contemplated Y that other types of tubes may be employed with 'Y equal facility without departing from the spirit or scope of the invention. The cathode ofthe tube I is connected to ground and-the anode is connected through a load inductor 2 to the posi tive terminal of a source of direct current such lector tube network includes series condensers 38, 39 and 4I, the latter of which preferably isV ad justable so as to provide for an adjustment in the natural oscillation period of the selector circuit. The shunt elements of the phase shifting net work are resistors 42, 43 and 44, the latter of which preferably is in the form of a potentiome ter„having an adjustable contact 45. The con tact` 45 is connected through a resistor 46 to the control grid 47! of the selector tube 32. The con-. >trol grid of this tube also is by-passed to ground by a condenser 43. Although the phase shifting networks associated with tubes I and 32 are similar, the output energy feedback to the input circuit, in the case of tube I, is suflicient to sus tain oscillation at a frequency of Y3!! cycles per second, whereas, in the case of tube 32, the feed as a battery 3, of which thelnegativeterminal ,is . back energy is insufñcient to sustain oscillation. connected to ground. The suppressor grid 4 of It is merely sufficient to enable the tube 32 to act the tube I is connected directly to ground and the 20 as a lfrequency selective amplifier responsive only screen grid 5 is connected through a resistor 6 to a frequency of 60 cycles per second. _ to the positive terminal-of the battery 3 and also In order to furnish a control voltage for driving through a by-pass condenser 'I to ground. the selector tube 32 at the desired frequency of The anode-cf the tube I’is connected to a triple 60 cycles per second, the anode of theY distortion mesh phase shifting network of capacitance and 25 tube 22 is coupled by an arrangement including resistance elements.` As illustrated, the network a condenser 43 and va resistor 5l to the control is formed of series condensers and shunt re grid 4l of the selector tube. Preferably, the sistors. It is contemplated that a network of resistor 5I is in the form of a potentiometer hav-series resistors and shunt condensers are within ing'an adjustable contact 52 >which is connected the scope of this invention. Condensers B, 9 and 30 bya resistor 53 to the potentiometer` contact 45 II comprise, respectively, the capacitance ele in the feedback circuit of the selector-tube 32 and ments of the first, secondïand third network also through a resistor 46 to the grid 4l of the meshes. The resistance elements of the succes tube. sive network meshes comprise, respectively, the The anode Vof the selector tube 32 is coupled space discharge path of a triode Vacuum tube I2, 35 by means of a condenser 54 and a potentiometer and‘resistors I3 and i4. The network is termi 55, having an adjustable contact 56, to the phase nated in a resistor I5, one terminal of which is comparator. This apparatus includes a diode 51 grounded and the other terminal is connected having an anode which is connected lto ground throughV a resistor I6 to the control grid Il of through a resistor 58 and also to the potentiome the oscillator tube I. The control grid also is 40 ter contact 55 through a condenser 59. YThe by-passed to ground by a condenser I8. cathode of the diode 5l is connected to an adjust- ' » 4The anodel of the oscillator tube I is coupled able contact 6I of a potentiometer 62, of which by a condenser I8 to the control `grid 2| of a the terminals are connected to a grounded source pentode vacuum tube 22 serving as the wave form of a standard 60 cycle alternating current sourc distorter, A resistor 23, connected between the 45 connected to the terminals 63. ' control grid of the tube 22 and ground,’serves as The automatic frequency control Voltage de the grid leak resistance for this coupling circuit. veloped by the phase comparator is impressed The screen grid 24 of the tube 22 is connected upon the frequency determining circuit of the through a resistor 25 to the positive terminal of oscillator tube I by means of a connection from the battery 3 and the suppressor grid 2B is con 50 the anode of the diode 5l through a resistor nected directly to ground. The anode of the 64 to the control grid of the triode I2. The con tube 22 is connected through an inductor 2l, trol grid of this tube is connected to an adjust which is by-p-assed by a condenser 28, and able contact 65 of a potentiometer 66 and also through the resistor 25 to the positive terminal of the battery 3. The cathode of the tube is con through a filter condenser 6l to ground. The 55 terminals of the potentiometer are connectedY to nected through a self-biasing resistor 29 to ground and a condenser 3l is connected to by pass the resistor 23. The self-bias voltage devel oped by this arrangement is to cause the tube to` operate in the anode current saturation'region. the terminals of a source of biasing voltagesuch as a battery 68. The anode of the. distortion tube 22 also is coupled to a high frequency selecting cir-cuit 69 by means of a condenser 1B. The selector 69 may be substantially similar to the selector in The apparatus for selecting the low frequency scanning Voltage of 60 cycles per second and the cluding the pentode tube 32, except that the phase voltage for comparison with the source of stand shifting network therefor is designed to operate ardizing frequency includes a pentode vacuum the high frequency selector at the line scanning ’ L tube 32. The cathode and the suppressor grid 65 frequency.33 of this tube are connected directly to ground. > 'I'he output circuit of the field scanning fre The anode of the tube 32 is connected through a quency selector including .the tube 32, is connect load resistor 34 to the positive terminal of the ed toa Vertical scanning generator 1l. Similarly, battery 3. The screen grid 35 is connected the output circuit of the line scanning frequency through a resistor 36 to the positive terminal of 70 selector 69 is connected to a horizontal scanning the battery 3 and also is by-passed to ground by ' a condenser 3l. As in the case of the oscillator tube I, the low frequency selector tube 32 is pro vided with a phase shifting network similar to that connected to the oscillator tube; The se generator 12. The scanning generators `-II «and 12 lmay be conventional and are not shown in detail herein for the reason that they form no part of the present invention. y Referring now to the operation of the illustra 5 atomes 6 tive embodiment of the invention, .assume that the oscillator tube l, together with Vits frequency determining circuit including the series con the condenser ‘50. .So long as the cathode and anode voltages arein phase the anode-to-‘cathotde potential of the diode remains constantxand vthe vdensers B, 9 and Il and the shunt triode I2 and current conduction .through .the .diodeand‘th'e 1re sistor 58 is'maintainedata .constant value‘w'hich is dependent upon the relative magnitudes :of the anode and cathode voltages. `A phase devia tion of .these `voltages effects a corresponding resistors I3, ld and l5, effects the generation of a voltage of sinusoidal wave form having a fre quency cf 30 cycles per second. This frequency is determined by the parameters of .the vphase shifting meshes connected between the output and input circuits of the tube. Each mesh, in change in the diode anode-.to-cathode potential cluding a series condenser, such as 9, and a shunt resistor, such vas I3, effects a Vphase shift, in `the instant embodiment of the invention, of approx imately 60° in the voltage of that portion of vthe energy delivered by the `output circuit ‘of the tube . to the `frequency Vdetermining circuit. Thus, « and, consequently„in .the value of .the current conduction through `the diode and the resistor 58. Thus, a unidirectional Voltageis developed in the resistor of a magnitude Vcorresponding `to the'rde gree of the phase deviation. This unidirectional voltage is combined with the biasing voltage derived from the potentiom eter 66 to form an `automatic frequency `control voltage. The magnitude and polarity of this con with the .three disclosed meshes of this charac ter, the voltage of Athis energy is shifted 180° in phase. trol voltage represents the instantaneousphase This phase-shifted energy is impressed upon the input circuit of the tube I in suiìicien-t 20 deviations of the oscillator derived 60 cycle volt-V age from the voltage derived from -the standard magnitude .to produce `sustained oscillations in izing source. The control voltage is` impressed the output circuit. The oscillator frequency may upon the grid of the triode l2 in the manner de be varied by adjusting one or more of the fre scribed. Any alternating current component qency determining circuit parameters, for ex ample, the value of one of the shunt resistors. 25 which may be present in the voltage derived from _ the output circuit of the diode 5l’ is substantially A modification of the shunt resistance consist eliminated from the frequency control voltage `by ing of the triode l2 will effect a change in the the ñlter condenser 6l. The control voltage im amount of phase shift produced by the first mesh. pressed upon the grid of the triode l2 effectively Consequently, a similar change will be effected in the total phase shift, thereby .to change the os 30 varies the impedance of the space discharge `path cillation frequency. of this tube. A variation in this impedance “ef fects a corresponding variation in the »degree >of The `.sine Wave voltage derived from the oscil phase shift produced in the first mesh' of the lator tube l is converted by the distortion tube 22 into a substantially rectangular wave form phase shifting network connected between the voltage having a frequency of 30 cycles per sec 35 output and input circuits of the oscillator tube i. Thus, the phase of the feedback energy impressed ond. The rectangular Wave form voltage is pro upon the input circuit of the oscillator tube is duced by driving the tube to saturation through the use of the self-biasing resistor 29. A rectan altered in one sense or the other, thereby to effect a corresponding change in the frequency of the gular Waveform `is referred .to merely for illus trative purposes, Substantially any distorted 40 generated voltage. The frequency of the voltage developed in `the wave form containing the desired harmonics will serve with equal facility. output circuit of the low frequency selector tube .A portion of the energy of the rectangular wave 32, ‘being 60 cycles per second, is suitable :for con trolling the generation of the field scanning volt form -voltage is employed to drive the low fre quency selector, including .the tube 32, in e, man 45 age since it is desired that this voltage @be `gener ated _at this frequency. The `harmonic of the ner to develop in the output circuit of this tube generated 30 cycle voltage, which the high- fre a substantially sinusoidal voltage having a fre quency selector G9 derives from the rectangular quency of 60 cycles per second which is the sec 30 cycle wave developed in the output circuit of ond harmonic of the generated frequency. The natural period of the network including the se 50 the distortion tube 22, produces a Voltage in the output circuit of the high frequency selector hav ries condensers 38, 39 and 4l and ythe shun-t re ing the desired line scanning frequency. sistors 42, 43 and 44 is substantially 60 cycles While it will be understood that the circuit per second. By means of the adjustment of the specifications of a scanning frequency generator potentiometer contact 45 the magnitude ofthe phase-shifted energy developed in the network is 55 embodying this invention may vary according to the frequency requirements of any particular maintained below the value necessary to sustain television system, the following circuit speci oscillations in the output circuit of the tube 32. fications for a generator employed to develop volt This energy is combined with enough 60 cycle en ages at 60 cycles per second and 15,750 cycles per ergy derived from the rectangular wave form voltage, as determined by the adjustment of .the 60 second are included, by Way of example only: potentiometer contact 52, to produce feedback Vacuum tubes 1 and 32 ______________ __ GAC?? Inductor 2 _________________ __henries" Battery 3 _____________________ __vo1ts__ `100 250 Resistors 6 and 36 ____________ __ohms__ 65 Condenser 7 ___________ __microfarads__ Condensers 8, 9 and 28 _________ __do____ 82,000 energy at 60 cycles per second of suiiìcient mag nitude to drive the tube 32 at this frequency. The phase comparator, including the diode 51, functions to detect deviations of the 60 cycle de rived frequency from .the standard 60 cycle fre quency. These frequency deviations are mani Condenser 11 _________________ __do___„ fested as phase displacements of .the derived volt Vacuum tube 12 _____________________ _l age wave with respect to the standardizing volt Resistors 13 ,14, 15, 34, 42, 43, 44 and age wave. iThe voltage of the diode cathode 70 53 ________________________ __ohnis_varies sinusoidally under the control of the stand Resistors 16 and 46 ____________ __do____ ardizing frequency voltage derived from the po Condensers 18 and 48____-micro-n1icro tentiometer 62. The voltage of the diode anode also varies sinusoidally under the control of the oscillator derived voltage impressed upon it by 75 farads ___________________________ __ 35 0.17 0.20 6C8G 10,000 330 200 Condenser 19 __________ __microfarads-- 4 Vacuum tube 22 _____________________ __ 6SJ7 2,407,956 7 8 Resistors 23, 58 and 66.A____ __megohm-Resistor 25 ________________ _\___ohms__ Inductor 27 ________________ __henries-- , 1 50,000` 17_ Resistor 29 --.___ ohms Condenser 31 __________ __microfarads“, Condenser 37 _________________ _»_do____ 25,000 0.5 40 Condensers 38 and 39 _________ __do____ 0.05 Condenser 41 _________________ __do____ 0.132 tions of a distorted wave for-m at a submultiple »frequency of a low frequency ñeld scanning volt~ age and containing a plurality of harmonics of Ul said submultiple frequency, means including a low frequency selector coupled to said oscillation producing means to produce a deilecting voltage for said television system at field scanning fre quency, and means including a high frequency Condensersl49~ and 70 _________ __do____ 0.5 Resistors 51 and 55 ________ __'___ol1ms__ 100,000 selector coupled to said oscillation producing Condenser 54 __________ __microfarads-- 1 television systemat line scanning frequency. Vacuum tube 57 ____________________ __ 6H6 means to produce a deflecting voltage for said 3. In a scanning frequency generator for a tele Condenser 59 __________ __microfarads-0.1 vision system, an electronic oscillation generator Resistor 62 __________________ __ohms__ 1,000 for producingsinusoidal oscillations at a submul Resistor 64 ___________________ __do____ 230,000 15 tiple frequency of a low frequency scanning volt Condenser 67 __________ _„microfarads__' 0.1 age, means for converting said sinusoidal oscilla Battery 68 _______________ __'_____volts__ 12 It is evident that a scanning frequency gen erator in accordance With the instant invention possesses a number of advantageous features not previously realizable in prior art systems. Since the line scanning frequency and the field scan ning frequency are not related harmonically in a system, where an odd number of scanning lines per frame and an even number of interlaced fields per frame are necessary, the generation of a sub-harmonic of the field scanning frequency makes it possible to dispense With the multiplicity of frequency dividers and/or frequency multi pliers required in prior art systems. -Also, when using an oscillator of the type described, the ap plication of an automatic frequency control volt tions into oscillations of a substantially rectangu lar Wave form, said rectangular oscillations being produced at said submultiple frequency and con-~ taining substantially all harmonics of said sub multiple frequency, a low frequency selector coupled to said Wave form converting. means to produce a control Voltage at the low scanning >fre quency, a generator coupled to said lowfrequency selector for control thereby to produce a deflect ing Voltage for said television system at ñeld scanning frequency, a high frequency selector coupled to said wave form Vconverting means to producea control voltage at the high scanning frequency, and another voltage generator cou pled to said high frequency selector Vfor control thereby to produce a deflecting volta-ge for said television system at line scanning frequency. age thereto in the novel manner disclosed makes 4. In a scanning frequency generator for a tele it possible to positively lock the frequency of the oscillator in a predetermined relationship to a 35 vision system, an electronic oscillation generator for _producing sinusoidal oscillations at a sub source of standardizing frequency. multiple frequency of a low frequency scanning K While there has been described what, at pres voltage, a distorting vacuum tube for converting ent, is considered the preferred embodiment of said sinusoidal oscillations into oscillationsof a the invention, itvwill be obvious to those skilled in the art that various changes and modifications 40 substantially rectangular wave form, said rectan gular oscillations beingproduced at said submulj may be made therein Without departing from the tiple frequency and containing .substantially all invention, and therefore, it is aimed in the ap harmonicsof said submultiple frequency, a loW pended claims to cover all such changes and mod- ‘ frequency selector including a driven oscillator iñcations as'fall within the true spirit and scope coupled tothe output circuit of said Ydistorting of the invention. tube to produce a control voltage at the low scan What is claimed is: ning frequency, the natural period of oscillation 1. In a scanning lfrequency generator for a tele of said low frequency selector oscillatorbeing Vision system, means for producing oscillations of equal to the low frequency scanning voltage, a a distorted Wave for-m at a submultiple frequency of a low frequency ñeld scanning voltage and ~ containing a plurality of harmonics of said sub multiple frequency, means coupled to said oscil lation producing means and controlled by a harmonicof said distorted Wave form oscillations to produce a deñecting voltage for said Vtelevision < system at field scanning frequency, and means coupled to said oscillation producing means and controlled by another harmonic of said distorted Wave form oscillations to produce a deflecting voltage for said television system at line scanning frequency. ` A 2. In a scanning frequency generator for a television system, Ymeans for `producing oscilla vertical scanning voltage generator coupled to said 10W frequency selector for control by said low frequency control Voltage to produce a de ñecting voltage for said television system at field scanning frequency, a high frequency selector coupled to the output circuit of said distorting tube to produce a control voltage at the high scanning frequency, and a horizontal scanning voltage generator coupled to said high frequency selector for control Iby said high frequency control voltage to produce a deflecting voltage for said television system at line scanning frequency. CLYDE E. HALLMARK.