US2421521A - Interlacing system - Google Patents

Description

June 3, 1947. W, 1 PQCH 2,421,521

INTERLACING SYSTEM Filed July 26, 1945 62 U 7 U I Ll MMT/317470K INVEN TOR.

ATTORNEY:

Patented June 3, 1947 UNITED INTERLACING SYSTEM Waldemar J. Poeh, Moorestown, N. J., assigner to Radio' Corporation of America, a corporation of Delaware Application July 26, 1945, Serial No. 607,112

(Cl. U23- 7.7)

7 Claims. Y l

This invention is directed to television apparatus, with particular emphasis being placed on a simplified form of arrangement whereby the interlaced patterns are obtained.

The many advantages of interlaced scanning are well known in the art, and the broad features thereof? have already been set forth, for instance, insuch prior art citations as the Ballard U. S. Patent No. 2,152,234, granted March 28, 1939, and in the Bedford U. S. Patent No. 2,178,218, granted Gctober 31, 1939. In scanning systems of this type, the successive line traces of one scannedraster or image field fall halfway between the scanning lines Of each of the preceding' and succeeding rasters or image fields. The result is that the traced image or raster appears to have twice" the number of lines that it actually has" and the' quality of the image' resulting is consi'd'eralblyV improved.

Various Ways" and means to achieve interlacing have already been proposed inr the art and, broadlyV speaking, the resultsv of interlacing are achieved by displacing the line scannings of successive fields" by one-half line length for alternate image fields. 4

This' effect is obtained by having a proper relationship' in frequency' between the horizontal and vertical or, inother Words, between the line and the field scannings. With present standard's,- the image fields are repeated at the rate of 60V per second, with two' neld's forming one complete' image frame, which frames occur at the rate of 30' perv second. The horizontal or line scannings now occur at a rate of 15,750 line traces per second. It thus'becomes' apparent that within the time allotted to scan' one raster or image' field (now 1/@0` second), provisions are ac- 'tuallly made for scanning only 2621/2 lines; but

with the 2621/2 linesv traced in the next succeeding raster' or image field, a 525 line image raster is' produced at' the' frame frequency, with the line" traces of each eld being placed intermediate those of the succeeding and preceding 'elds.

With" apparatus' of the prior art, the complexities of suctipattern' traces usually' require that a vccniplex sync signal generator be associated with the'V vi'de'o or image signal producing equipment- OneV example of a form of sync generator for such'v a purpose has been exemplified by patents already granted to J. P. Smith, such as U. S. Patent Nos. 2,132,654 and 2,132,655", to name but two such-l patents way of example. Further representations of this general form of apparatus may be foundl alsobyjreference to the Seeley'UL S, Patent No;v 2,256,530', the Bedford U'. s. Patent No 2,258,943, andthe Schlesinger U. S. Patent No.v 2,350,536-, granted June 6, 1944.

In the present invention, effortsl have been inade, lio-Wever', to simplify very considerably the the instrumentalities used to develop the linel i sync pulses are keyed on to the control of the assumed 60-cycle field frequency pulses in such away that any two successive image Iields or rasters are scanned with one-half line time delay so that exact displacements between the lines: of successive image iields` are obtained, and an odd number of fields, for instance, trace the oddnumbered lines of the complete image frame, and even-numbered fields trace the even-numbered lines of the complete image frame.

Broadly speaking, these results are achieved through the utilization of an appropriate ferm of line frequency pulse generator-` Which is keyed on and off completely under the control of the unit which brings about the field deflection, so that the line frequency sync pulse generator has its operation completely arrested for avery limited time period under the control of the' field frequency pulse in order that it may be restarted to bring about the desired form of deection control pulse. Thisl procedure thus brings about a so-calledsynthetic, even though' effective, interlacing method.

It, accordingly, becomes an object of this invention to provide a simplified form of system to bring about adequate and proper interlacing of successive scanned image rasters.

It is also an object of this invention to provide a form of scanning unit in greatly simplified form which overcomes one or more defects found to exist in presently used apparatus and, at theY same time, to provide highly efficient units of economical construction.

Other objects and advantages will' suggest themselves promptly to those skilled in the art to which the invention is directed when the invention is considered in the light of the accompanying drawings, of which the single gure, together with the diagrammatic representations of wave forms shown adjacent to signicant portions thereof exemplify in one form a suitable and efficient arrangement to bring about the results above set forth.

Referring now to the drawing for a further understanding of this invention, line frequency output signals for triggering a suitable horizontal discharge tube (not shown) which is associated with cathode ray beam deflection control apparatus, for instance', are developed by a line frequency or horizontal multivibrator unit generally represented at I I'.

This multivibrator unit I I comprises essentially a pair of thermionic tubes I2 and I3' which are cathode coupled With the cathode elements I4 and I5 thereof being. connected by a conductor I6 which connects to ground I'I by way of a variable cathode load resistor I8. The grid or control electrode I9 of the rst tube l2 connects to ground I'I by Way of the resistors 120 and 2|. The grid or control electrode 22 of the second tube I3 connects through resistor 23 to the junc-y tion point of the resistor elements '25 and 2l.

Likewise, through the well known coupling condenser 24, the output signals from the plate or anode 25 of the first tube I2 are supplied to the grid or control electrode 22 of the second tube I3. Each of these tubes I2 and I3 has the plate or anode element 25 and 26 thereof, respectively, supplied with a suitable positive voltage by way of resistors 21 and 28, respectively, which connect to a terminal point 29 whereat the positive terminal of a suitable source of voltage (not shown) is connected. This voltage source preferably has its negative terminal suitably grounded.

The same voltage source provides the plate Voltage for a keying tube 30, later to be explained, by way of its connection through conductor 3l to the plate or anode 32 of such keying tube and the resistor element 3.3 forms a part of the plate load of the keying tube. The cathode element 34 of the keying tube 3l) connects by way of the conductor 35 to each of the cathodes I4 and I5 of the multivibrator tubes I2 and I3 so that the tube 30 may serve, in a manner later to be explained, either to initiate or to interrupt operation of the multivibrator unit.

The output pulses from the multivibrator unit above explained are pulses which occur in accordance with circuit constants or parameters selected for the circuit of the multivibrator unit. These pulses are of short duration as compared to their interruption period and occur for presently proposed forms of standard apparatus at a repetition frequency of 15,750 pulses per second. The output pulses thus obtained are shown diagrammatically adjacent conductor I6 between the cathode elements I4 and I5 of the tubes I2 and I3. These same pulses are fed to the output conductor 36, for instance.

Simultaneously with the development of the pulses for controlling the horizontal discharge tube, other pulses known as the vertical or eld frequency control pulses are developed from a completely separate oscillator unit, schematically represented at 4I The vertical pulses occur at a frequency of 60 per second, for instance. The vertical oscillator may be of any desired type and, for instance, might be a multivibrator of the general type above described for developing the line frequency pulses except that the circuit constants would be of considerably different values to provide the difference in frequency of the output from each of the multivibrator units.

Also, while a multivibrator unit has been shown above as developing the line frequency pulses, it will, nevertheless, be apparent that it is within the scope of this invention to utilize other forms of pulse generators, such as the well known blocking oscillator, for instance, to accomplish the end objectives obtained by the multivibrator.

The vertical pulses developed in the unit 4I are then fed through a vertical discharge tube of Well known character, which is schematically represented at 42. The output from this vertical discharge tube is then supplied through a condenser 43 to the grid or control electrode 44 of a vertical output tube 45. This tube has its grid or control electrode 44 connected through the leak resistor 46 to ground I1. Its cathode 41 is 4 provided with bias through the cathode resistor 43 connecting to ground.

Output signals which appear at the plate or anode 49 of the output tube 45 may be generally of sawtooth wave formation as represented diagrammatically by the curve adjacent the output terminal. Suitable plate voltage for the output tube is provided at a terminal point 5I to which a source of Voltage (not shown) is connected in a manner similar to the connection specified at terminal point 29. This voltage feeds through the primary Winding 52 of the output transformer 53. Any output signals correspending to those indicated are then suitably fed into the transformer secondary 54 to be supplied to suitable deflection coils, for instance (not shown).

Also connected to the plate or anode 49 of the output tube 45 is a differentiating circuit comprising the serially connected capacitor 55 and the shunt connected resistor 56, having one terminal thereof connected to the side of the capacitor remote from the tube anode 49 and the other terminal thereof grounded at II. Output signals of the indicated wave form are, therefore,

differentiated by means of the differentiating network so that at the point '51, wave forms of generally short pulse character appear, as is in.. dicated by the curve shown adjacent this point.

These pulses are supplied through the resistor 58 to the junction point 59 whereat they are mixed and combined with the differentiated output pulses from a 30 cycle multivibrator unit, generally designated as 60 and later to be described. The combined pulses Will then be fed by way of the coupling condenser 6I to the grid or control electrode 62 of the keying tube 30, heretofore described, which is suitably biased by a source of negative potential connected at terminal 63 at the lower end of the grid resistor 64. This operation will later herein be described.

The pulse signal available at the point '5l is supplied in reduced amplitude through the conductor 61 which is adjustably connected to the resistor 56 in accordance with the position of its slider point 68 thereon. The signals thus supplied through conductor 51 then serve to trigger and suitably control the multivibrator unit 60 through application directly upon the grid or control electrode 69 of the rsttube Ill of this multivibrator unit.

The multivibrator unit 60 is of essentially the same character device as the line frequency multivibrator II except for its circuit constants. It comprises a first tube 'I0 and a second tube 1I. The cathode elements I2 and 'I3 are connected together through the conductor I4 and to ground I1 through the variable cathode resistor 15. The plate electrodes i6 and 'I1 receive plate voltage from a source (not shown) connected with the terminal point 'I'I in a manner similar to the above explained connection at terminal point 29. The output from the first tube 'Ill is fed from the plate 76 thereof to the input grid or control electrode 'I9 by way of the coupling condenser 8| in the manner already explained above. The grids or control electrodes of each of tubes 'I0 and 'H connect to ground, for instance, through resistors 82 and 83, respectively.

Output pulses from the multivibrator unit will be developed under the influence and control of the keying pulses made available at point 68 by reason of the differentiating network 55, 56 so that pulse output signals repeating at 30 pulses per second may be made available from the unit .5 -60 `where lthe :circuit parameters are appropriately chosen 4so that the unit :triggers once -for every second pulse available at the point 51 or 68.

:Pulse -output .at the -30 c-ycle frequency may tbe obtained in this manner in the conductor .'81 and it will fbe of the general wave .-formindicated immediately thereabove. As these pulses "are then supplied through `a serially connected Adifferentiating Ine'tvvork'comprising .the capacitor `88 -and the resistor-:89connecting to ground, as-indicated, they -will be Adifferentiated -and assume a Wave form :somewhat like that shown -above "the Vjunction poi-nt 90. The Wave form thus is aninteryrupted series of 4pulses which `Will be found to extend in both the lnegative and positive #directions by reason -of .the drlTerentiation v of -the Wave appearing :in conductor 89. 'Ille differentiated .pulse may then be -supplied `by way of the mix-ing or combining resistor 93 to combine at the `junctionpoint 59 with lthe pulseoutput appearing at the :point 51.

The complete signal series of the schematically indicated wave for-m is such that `the portionla' of Athe Idifferentiated output signal from the multivibrator unit '160 coincides substantially inits initiation with the commencement of the pulse portion a of the signal output available at the point 51. However, since the multivibrator unit lill provides output pulses at 30 cycles, which is half the Yfrequency at which thepulses -available lat point 5.1 occur, there Will 'be-no'output signal from the multivibrator unit 60 available at the point l59 when lthe signal pulse b larrives at V*this point. The next pulse a will, however, commence coincidentally with the next following ,pulsen which appears at point 51.

By adjusting the 1resistor 93,"the amplitude of the gpulses .a `which are vmade available at the combining point 59 can be controlled. Accordingl-y, with an additive combination-of the differentiated pulse series from vthe ymultivibrator unit .Gill and the Vdifferentiated output pulses from .the output tube 44, it will be appreciated :that `the negative Aportion A'a' of .the output from Ithe multivibrator unit EU will tend -to subtract from the .pulse c so as to remove effectively .the leading portion vthereof. In this way, the effective time of commencement of the pulse a in the circuit beyond vpoint 579 can be changed relative to the timeof commencement of the pulse b so that by 4properly adjustingthe resistor value.93, the -leadving `edge of the pulses a, vfor instance, can be shifted in time relationship with respect -to xthe vpulses b .by a time period which would coincide vwith the time allotted to exactly a one-half line .f

scanning period, or to .one-half lthe time represented -.by 'thefseparation .of the output pulses of horizontal .frequency available vin the conductor 36.

. If now the'combined pulse series which -is available at Ljunction -point 59 issupplied Ito the grid or -control `electrode yB2 of the keying'tube 1,30, `it Will be yappreciated vthat this tube immediately commences .to draw -plate current during each positive pulse portion. With the cathode output from the keying tube being derived across the cathode resistor 8 and with the cathode 34 of the keying tube .39 following the potential of the grid .62 .any application 4of .pulses of positive polarity on the grid 62 causes thecathode 34 immediately to assume a positive potential.

The connection of this cathode element 34 throughconductor 35 to the-.cathodes I4 and t5 of 'the 4multivibrator tubes |12 sand i3, completely arrests the operation of the multivibrator unit .|:I Leach time a positive y:pulse appears on the control grid 'B2 of the keying tube. Since suc- ,cessi-ve .pulses of positive polarity on the grid ,62 of the :keying tube -30 :are shifted in time relationship with respect to each other, ,fat a `time period coinciding with one-half the period .between Asuccessive -line frequency pulses, it becomes apparent that for each :successive `vertical field, Vthe lline :pulses are devloped at ldiilerent times. This, fthenprovides-an yalternate start land interruption .of the -line frequency multivibrator in `accordance with the control rdirectly exercised thereon tby ithe vertical :oscillator YM and causes the :line .of successive fields 'to `be scanned 'one haii dine tperiod apart so `as synthetically :to give the 'elect `of `interlacing the lines of successive elds and to cause each traced raster to Ahave its lines luniformly'displaced with respect to each lpreceding :and succeeding raster.

In connection with vthe invention the 4broad lfeature Vof ,the 'control :is that of keying the line frequency generator under .the control of Vthe neld 4"frequency pulses which are modified by the lower Tfrequency `pulses -so as to start -at idiierent time wperiods relative to each other.

Having 'now described the invention what .fI claim is:

l. "In a :television circuit vfor developing .signal -pu'lses ,for controlling the linear 4deilection fof Aa cathode ray `Ybeam utilized to trace :a predetermined lraster which comprises, :in combina-tion, a :substantially :stable oscillator means -to generate line :control pulses at ;a selected line i-requency frate, :means to `develop `supplemental foontrol pulses occurring at .substantially 1a desired rastereld repetition rate, `means for producing from the supplemental pulses asequence =.of oscil lator control pulses spaced in time relationship Vsuch that successiye pulses :cocu-rat time :periods which are eunequal'ly :spaced fro-m 'the vpreceding and 'succeeding lpulses, vand `means responsive -to the produced oscillator 4control pulses rior-rendering the dine frequency pulse generator inoperative during :periods ,at which the `said .control pulses are-produced :and for initiating an :operation of .1i-,he line frequency pulse ,generator during periods zintervening Ebetween successi-ve pulses.

2. In :a ftelevision circuit for y"developing signal pulses Yfor controlling `the linear deflection voi aa cathode :ray ib'eam .utilized vto .trace a predetermined `caster which comprises, 4gin combination, a substantiallystable oscillator means vto gencrate line control 'pulses rat a selected .line frequency irate, .means to Adevelop fsupplementalcontrol pulses loccurri'ng iat substantially a desired raster field erepetition irate, means for producing Ifrorntloe supplemental'gpulses a sequenceofosci'llater 'control 'gpuglses :spaced i-n time :relationship such'th-at successivefpulses occur at 'time lafieriods which Lare unequally yspaced `trom the preceding andfsucceedingfpulsesnand a keying tube responsive to the ,produced :oscillator control pulses :for interrupting oompletelytheoperation of the line frequency -pulse generator during periods at which Vthe Asaid ,control -pulses are :produced and Ifor Vinitiating :an opera-tion of .the yline lfrequency pulse ,generator immediately -upon cessation cof the Ycontrol pulses and vfor time :periods 'interi/en ing between r*successive pulses.

3. In -a television `circuit Vfor developing signal pulses yfor controlling the :linear A.dei-iection :of a cathode fray Fbeam v:utilized to -tiace a ipredetermined raster which comprises, lin combination, a substantially .stable oscillator means to gencrate line control pulses at a selected line frequency rate, means to develop supplemental con; trol pulses occurring at substantially a desired raster field repetition rate, means for producing from the supplemental pulses a sequence of oscillator control pulses spaced in time relationship such that successive pulses occur at time period which are unequally spaced from the preceding and succeeding pulses, and a keying tube having its input circuit connected to receive the produced oscillator control pulses and its output circuit connected to control the operation of the line frequency generator by rendering the line frequency pulse generator inoperative during periods at which the said control pulses are produced and by initiating an operation of the line frequency pulse generator during periods intervening between successive pulses.

4. In a television circuit for developing signal pulses for controlling the linear deflection of a cathode ray beam utilized to trace a predetermined raster and to synthetically interlace successive rasters which comprises, in combination, a Substantially stable line frequency oscillator means to generate line control pulses at a selected line frequency rate, a second substantially stable oscillator means to develop supplemental control pulses at a selected raster repetition rate, means for producing under the control of the supplemental control pulses a sequence of nonuniformly spaced line frequency oscillator control pulses so spaced in time relationship that successive pulses occur in time periods which are unequally spaced from the preceding and succeeding pulses, and a keying tube having its input connected to receive the combined series of pulses and its output connected to the line frequency generator, said keying tube means operating under the control of said last named pulses and being adapted to render the line frequency pulse generator inoperative during periods coinciding with oscillator control pulses and to initiate the stable operation of the line frequency pulse generator during periods intervening between successive oscillator control pulses.

5. In a television circuit for developing signal pulses for controlling the linear deection of a cathode ray beam utilized to trace a predetermined raster and to synthetically interlace successive rasters which comprises, in combination, a substantially stable line frequency relaxation oscillator means to generate line control pulses at a. selected line frequency rate, a second substantially stable oscillator means to develop supplemental control pulses at a selected raster repetition rate, means for producing under he control of the supplemental control pulses a sequence of non-uniformly spaced line frequency oscillator control pulses so spaced in time relationship that successive pulses occur in time periods which are unequally spaced from the preceding and succeeding pulses, and a keying tube having its input connected to receive the combined series of pulses and its output connected to the line frequency generator, means for energizing said keying'tube under the control of said last named pulses and thereby applying a biasing voltage upon the line frequency pulse generator to render it inoperative during time periods coinciding with the duration of oscillator control pulses and for removing the biasing voltage and initiating stable operation of the line frequency pulse generator during periods intervening between successive oscillator control pulses.

6. In a television circuit for developing a plurality of signal pulses for controlling the deflection of a cathode ray beam to trace a predetermined raster which comprises, in combination, means to develop eld frequency control pulses normally produced at a predetermined rate, means to generate line control pulses normally produced at a substantially constant rate, means to develop supplemental control pulses at a rate such that successive supplemental pulses occur coincidently with substantially alternate eld frequency control pulses, means for differentiating the eld frequency and supplemental pulses and for combining the said pulses additively whereby the additive series comprises a sequence of pulses which are each non-uniformly spaced in time relationship with respect to the preceding and following pulse, and a keying tube having its input connected to receive the combined series of pulses and its output connected tothe line frequency generator, said keying tube being adapted to render the line frequency pulse generator inoperative during periods coinciding with pulses ofthe combined series o-f pulses and to initiate an operation of the line frequency pulse generator during periods intervening between Vsuccessive pulses of the combined series.

7.In a television circuit for developing a plurality of signal pulses for controlling the deflection of a cathode ray beam to trace a predetermined raster which comprises, in combination, means to develop iield frequency control pulses normally produced at a predetermined rate, means to generate substantially constant frequency line control pulses at a frequency which is a selected non-integral multiple of the field frequency pulses, the non-integral relationship being such that line frequency pulses of a number corresponding to nl-m normally occur within the time period between each successive field frequency control pulse, where n is a whole nurnberand m is a fraction of the order of one-half, means to develop supplemental control pulse energy at a rate such that one supplemental pulse is developed following a pluralitf,T of eld frequency control pulses, means for differentiating each of the neld frequency pulses and the supplemental pulses and for combining the said pulses additively whereby the additive series comprises a sequence of pulses non-uniformly spaced in time relationship with the variance in spacing between the successive pulses being of a time period corresponding substantially to the order of a fractional part of the time intervening bctween two successive line frequency pulses at the selected repetition frequency, and a keying tube having its input connected to receive the combined series of pulses and its output connected to the line frequency generator, said keying tube being adapted to render the line frequency pulse generator inoperative during periods coinciding with pulses of the combined series of field and supplemental pulses and to initiate an operation of the line frequency pulse generator during periods intervening between successive pulses of the combined series.

WALDEMAR J. POCH.

REFERENCES CITED FOREIGN PATENTS Country Date Great Britain Oct. 28, 1935 Number

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