US2249532A - Synchronizing and rackground control for television receivers - Google Patents

Description

July 15, 1941. H. M'JLEwls sYNcHRdNIzING AND 'BACKGROUND CONTROL' Fon TELEVISION REGEIVERS 'Filed neo. "2. 1937 4 Sheets-Sheet` 1 ATTORNEY HjM. L EIwlsi l2,249,532

Filed Dec. 2,.,1237 4 Sheets-Sheet 2 LD M. LEWIS INVENTOR July-15, 1941.

sYNcnRoNI-zme im BACKGROUND conTRQL Fon TELEvIsIoN REcmvEns ATTORNEY July 15,1941.v H. MLx:w|s

'sYNcHRoNIzING AND BACKGROUND CONTROL FOR TELEvIsIIoN REcEIvERs Filed Dec. 2. 1937 sheets-sheet 5 zu: mmm

4 ATTORNEY HJM. L Ewls r 'sYNcHRoNIzING -AND mwmsfRoLmD lcoNllRoI. Fon TELaVIsrL-RECEIVERS July *'15,v 1941.

Filed Dec. 2 2, 11337 4 sheets-sheet 4 J f c c c @9mm c E P c c c t c o dos. L F r .mda

mda 4 4 l P @am u .vdi

INVENTOR H RoLD M;|.|:w|s BY 2 i! ATTORNEY- j Panarea July 1s. 1941,.'

'Beleid G ND BACK-GROUND 00N- mli l'lLlVlSIOHECEIVEBS fil. N. Y... mime to a vcorporation oi Delaz. rsa1. sensi Nt. r1-mss' invention relates to television synchronixing and background control systems for tele vision receivers adapted to receive and video-frequency components, bachground-illumi nation components, and synchronizipgeompccents-including linefsynchronizingand deldvsyn chronising impulses having values outside the.'

amplitudeQrange of the videoireqllenCY ments.

K comprises a carrier, modulated (hiring sucessive intervals or trace periods by `video` irequency' components representative of the iightand -shade vaiuesoi an image being transmitted. ,Quring retrace intervals, between the trace periods.` thecarrier' ismodulated oy synchronizing impulses or-components which correspond to the initiations ot successive lines and elds inthe scan if-ot the image. There is also usually devel- `operi Vat the transmitter s unidirectional voltage whichcorresponds to the average background illumination of the image. While this voltage may be lost during transmissiomthe signal as received includes a component from which aunidirectional voltage representative of background illumination may be reproduced. At the recelver,'a beam is so deflected as to scan and illuminate a target in a series o! neids oi parallel lines. The videofrequency `and background illumination components of the received signal are utilized to control the intensity of the beam.v The iineand ilcldfscanning synchronizing components are separatedfrorn the video-frequency components andi-trom each other and utilized to synchronize I V the "operation of the receiverline and ileldapparatus rwith the similar apparatus utilized at the transmitter in developing the signaL The transmitted imase is thereby reproduced on the target of the receiver.

Iii-scanning oi the interlaced type. the line and.

neld frequencies are so related that successive nelds are stlered, the lines oi oneiieldialiinl between or inter-lacing those of a preceding iieid due to persistence of yisiom-the optical eitect'iiroduced is as though each frame or will! o! n elfcomprised a multiple o( the actual nuxit-- berfoi lines scanned per neid and the' iramcscaniiingfreouency equalled the held-scanning Various types ci carrier signal modulation- Vandl-.synchronizing methods and alwa- `ratus 4heretofore Yh've been The time or usual-which n required loraiuce a video-irequency signal. 'iipbined (cuirs-1.5)

narily depends upon the type signal employed and the type oiscanning utilised.

Eoresample. in certain systems negative modulati'on isempIPyedLthat is, ai decrease in carrier by increases in the carrier amplitude where inc ir-v ative`video modulation is employed and by de#- l5 creases in carrier amplitude where positive vide modulation is employed.

vIn interlaced scanning systems. certain ofthe held-.synchronizing impulses necessarily occur between line-synchronizing impulses. In order that lthe lineand frame-synchronizing impulses may be successfully separated from".I the video-frequency components and from each other and uti; iized, various types of synchronizing signals and separating apparatus have been proposed, such -as ion-example signals in winch the field-synchronizing impulses are of greater height or of longer duration than the line-synchronizing impulses, ad separating apparatus comprising amplitude discriminating or integrating circuits. 30

z to be subject to various objections such as being unstable, requiring an 'undesirably large portion ciuding video-frequency'components,background.

illumination components and combined synchro- -nizing components, thevideo-irequency compo-f so nents and a unidirectional voltage representative tively separating the synchronizing components iromeaohother.- l

invention. a television mtem for receiving and reproducing n video amplitude 'corresponds to an increase in iilumiA natioovhlle io' other srstmspositive vmorluls- 'Y tion-is L.utilized in which an increase" in carrler amplitude corresponds to an' increase in iiluni nation; -r'ihefsynchronizing components'oi the" In accordance with present television practice'. t there is developed and transmitted c signalylhich Such arrangements, however. have been found oi the total carrier amplitude, and involving rela-` oi the background illumination, well as eiiecchronizing impulses from each other.

components, and synchronizing componentsA including line-synchronizing and field-synchronizing impulses having amplitude values outside the amplitude 'range of the video-frequency components comprises, a single rectifier and associated load circuit for simultaneously deriving from the signal a unidirectional-bias voltage representative of background illumination and effectively separating the line-synchronizing and field-syn- 'I'he system comprises also means for utilizing the effectively separated synchronizing impulses for synchronizing separate scanning operations of the system and means responsive to the above-mentioned bias voltage for controlling only the background illumination of the image reproduced by the system.

In the preferred embodiment of the invention, the line-synchronizing impulses have leading edges of steeper slope than their trailing edges while the field-synchronizing impulses have trailing edges of steeper slope than their leading edges, these respective impulses being separately developed and combined to develop the composite synchronizing signal. Dii'ierentiating apparatus at the receiver derives from the composite synchronizing signal, a synchronizing signal in which the line-synchronizing and framesynchronizing impulses are poled in opposite senses. Hence, this derived signal may be utilized to effect synchronization of line-scanning apparatus entirely independently of the frame- Vquency components, background-illumination wave generator I2, the output circuits of these generators being connected to. the scanning elements of the signal generator Il in the usual manner. In order to block out the cathode-ray of the generator Il during the retrace scanning periods, there is provided a block-out wave generator I3 having its output circuit suitably connected to the signal generator Il. For providing impulses to suppress undesirable Signal impulses during retrace scanning periods and to insure proper form of the modulation signal to be developed, there is provided a pedestal imexample, to the power Supplyv circuit or fo the synchronizing impulses and to effect synchronization of the frame-scanning apparatus entirely independently of the line-synchronizing impulses by simply applying the synchronizing wave to the scanning apparatus with the proper polarities.

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 its scope 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 useful in generating a television signal for application to a receiving and reproducing system constructed in accordance with the invention: Fig. 2 is a circuit diagram, partially schematic, of a complete television receiving system embodying the invention; and Figs. 3-9 are curves illustrating the wave forms of periodic current or voltage waves developed at different points in the systems of F188. 1 and 2 to aid inI the understanding of the invention.

Referring now more particularly to Fig. I of the drawings, there is illustrated a television transmitting system of a type useful in generating a television signal including combined videofrequency components, background-illumination components, and synchronizing components including line-synchronizing and field-synchronizing impulses having amplitude values outside the amplitude range ofthe video-frequency components for application to a receiving and reproducing system in accordance with the invention, and comprising a signal generator Iliwhich may be of a conventional design including the usual cathode-ray Signal-generating tube and scanning elements. For developing scanning voltages or currents for thegenerator Ii, there synchronizing voltage source of a motion picture mechanism, where such is employed.

.Connected in cascade to the output circuit of the signal generator Il, in the order named, are video-frequency amplifiers Il, I! and 2l, a modulator 2| and associated coupled carrier-frequency oscillator 22. a power amplifier 23, and an antenna system 24, 2i, all according to conventional practice. The output circuit of the'pedestal generator Il is coupled to the video-frequency amplifier Il, while the output circuit of the synchronizing signal-generating apparatus Il is coupled to the video-frequency amplifier 20. Suitable means (not shown) may also be provided for developing a unidirectional background control voltage and applying the same to the amplifier Neglecting for the moment the details of the synchronizing signal-generatingA apparatus Il,

and accelerated toward the target in the usual manner.A Scanning or defiecting currents or voltages developed bythe generators II and Il, areappliedtothescanningelementsofthegemerator Il to provide electric fields which serve to deflect the Acathode-ray horizontally and verticalLv thereby to scan successive series of. parallel lines or fields upon the target. The defiecting currents or voltages and, hence, the scanning fields, are of well-known saw-tooth wave form.

providing a relatively slow linear trace and rapid retrace. The number of lines per field is determined by the relative value of line`- and framescanning frequencies.A The frequency is preferably a multiple (which. is an integer plus a fraction) of the eld frequency so that the succesaieneldsofparallellinestracedonthe target interlaced in the well-known manner. The scanning frequency may, for example. be 13,2# cycles and the field-scanning frequency assassin.

il for synchronization, while its output circuit 60 cycles per second, respectively. Block-out impulses developed bythe generator 'are applied to the control electrode of the cathode-ray tube to suppress or block out the beam during retrace portions oi the scanning cycles. while pedestal impulses developed by-the generator il are applied to the amplifier II to suppress surges which is coupled to a so-called short memory ciroccur and set the level at black during each line and field retrace interval.

The synchronizing impulse signal developed by the apparatus I is applied tothe modulation ampliiler. while the timing impulses developed by the generator It are applied to the generators lI-UL inclusive, in the apparatus Il to lock these generators and apparatus in synchronlsm.

The photosensitive elements of the target in the cathode-ray tube of the generator Il being electrically affected to an'extent dependent upon the varying values of light and shade at the corresponding lncremental areas of the image io- The device Il may comprise a pentode vacuum tube 3| havinga condenser 32 included in its anode circuit in parallel with a high impedance teed resistor u. by way ot which operating potential is supplied to the anode of the tube from a suitable source as indicated atV +B. while a suitable potential is applied to its -screen ironi a source indicated at -i-Sc. The input circuit of a liiniter and amplifier. M is connected across cused thereon, as the cathode-ray scans the tarf get, a video-frequency voltage of correspondingly. varying amplitude is deveolped in the output circuit oi the generator'l il and applied to the video-frequency amplifierl Il. whereinthis 'voltage is ampliiied and from which it is'translated to the amplifier I9. Where a unidirecpliiler 2l as'explaied above.

tional. back-ground illumination voltage has been developed by suitable means (not shown) it may also be applied to the ampililer` Il. Here the video-frequency voltage is further amplled and c mixed with the unidirectional voltages and with pedestal impulses supplied from the generator i4. The amplified mixed voltages' in the output v circuit of the amplifier r-ls are thereupon applied to the amplifier 20, wherein they are further amplified and mixed with the synchronizing impulse signal supplied from the apparatus Il.

The modulation voltages are thereupon supplied to the modulator 2i, wherein they are so liripressed upon the carrier wave generated by the oscillator 22 as to .develop a positivelymodulated-carrier such as described above. Theresultant modulated-carrier signal is delivered to the power ampliner 23 for ampliiication and'is thereafter impressed upon the antenna system,

24, 25 to be broadcast.

Referring now more particularly to the apparatus i5 provided for the purpose oi developing line-synchronizing impulses, there is provided'a generator 2E, which may comprise signal-generating apparatus oi any suitable conventional' type adapted to develop `periodic impulses o! linescanning frequency, for example. 13,230 cycles per second, and of rectangular or peaked impulse wave form, as indicated immediately below the generator 20. The input circuit of this generator is coupled to the timing generator il for inthe operation of the synchronizing signalgenerating apparatus l5, the generator 2G, synchonized by the timing generator Il. serves to develop a periodic rectangular or peaked impulse A`wave oi'l line-scanning frequency and to deliver this wave by waywoi'the limitera and ampliiiers I'l and 2l wherein, dueto their limiting and amplifying action, there vare developed periodic,.linesynchroniz1ng impulses having leading edgesA of steeper slope than theirtrailing edges. as indicated4 by the wave adjacent the limiter andampliiler 2l.

The generator 29, synchronized by the timing generator II, serves. to develop.- a periodic rec'- tangular impulse wave ot the desired iield-scaning irequency'and this wave is applied to' the grid oi the tube 3l of the short-memory circuit I. with auch polarity that the grid is positive during the trace portion of each cycle, that' is din-ing the periods between the impulses. when path across the condenser l?. During the short retrace periods, that is. for duration of the impulses, the grid is made highly negative so that the condenser charges exponentially by way of the resistor il. .Y At the termination of each Y impulse. the condenser I2 is again shorted bywayoi' the anode-cathode 'conductance of the tube-and discharges more raidly, .The resultant voltage impulses developed across thecoudenser Il. therefore, have leadingedgesof relatively synchronization, while its output circuit is cou- 4pierre s' limiter and` amplifier i1 having its ouput circuit connected in-turn to a further limiterl and ampiliier' 28. The limiters and amplifiers may comprise any 'suitable conventional circuit arrangement, including, for example, vacuum tubes so biased as to cut oif predetermined portions of the applied waves.

For the purpose oi' developing frame-synchro-l nizing impulses there is provided a generator 2l, which may be of any suitable conventional construction adapted to develop a periodic impulse' wave oi the' desired iield frequency. for example, '60 cycles. thciinpulses of which are of ri'a'ctan'gular form as indicated immediately 3-9. inclusive. below this generator. The input circuit of the i 'generator 2Iis"'coupled to the-timing generator 16 tem there illustrated comprises a gradual slope and terminating edges of steep,-

.slope as indicated by the cu'rve immediately below tube li. The limiters'and amplliiers 3l and ll serve to cut oi! the upper and lower portions of these impulses. thereby to develop held-synchronizingimpulses of. thedesired wave form, 1

such as indicatedV adjacent the limiter and ampliiier Il. -v n nie line-synchronizing and field-synchronizing impulses are combinedin the mixing ampliiier Il and applied to the amplinerllas mentioned above. The significance oi' shapes of the synchronizing impulses will be better u nderstood in connection with thejriollowi'ng 7o scription of receiving ,apparatus es'nbodylng .the

the systeminconnectionwiththecurvesoi'ligs.

Referring more particularly to rig. a'. uis systhe tube Il Y constitutes a low resistance shunt lilcd to the output or the video-frequency ampliiier 4I by way ot suitable synchronizing signal-separating apparatus Il and to the scanning elements of the cathode-ray tube. umts I`|44, inclusive, 4i and 46, may all be of conventional well-known construction so that detailed illustrations and descriptions thereof are deemed unnecessary herein.

Reierring briefly to the operation of the recelving system, television signals transmitted,v for example. from a system such as shown in Fig. 1 .and intercepted by the antenna circuit 31, 38. are selected and ampliiied in the radio-frequency ampliiier 39 and supplied to the oscillator-modulator 4l wherein they are converted to intermediate-frequency' signals which, in turn, are selectively amplified in the intermediate-frequency -ampliiier 4I and delivered to the detector 42.

The modulation components of the signal are derived by the detector 42 and are supplied to the video-frequency I amplier 43 wherein they are ampliiled and from which they are supplied to a brilliancy-control electrode of the cathode-ray tube 44. '.lllie intensity or the electron beam of the tube 44 is thus modulated or controlled in accordance with the video-frequency voltages impressed upon the control electrode of the tube in the usual manner. The modulation components are also supplied to the apparatus I3, wherein `synchronizing components are separated :from

:the video-frequency components and the linesynchronizing and trame-synchronizing impulses are effectively separated trom each other. as further explained hereinafter, and applied tothe generators 4I and 46, respectively. Saw-tooth current or voltage scanning waves are generated by the line-frequency and trame-frequency generators 4i and 4I, which "are controlled by the .synchronizing impulses supplied from the apv paratus and the scanning waves are applied tothe scanning elements of the cathode-ray tube 44, to produce electric scanning fields, thereby todeilecttherayverticallyandhorlmntallyso astotracesuccessive interlaced nelds of parallel linesonthescrccnoi'thetube,toreproduce the -Reterring now more particularlyto the por- The stages or from the signal a back-ground illumination control voltage as well as for effectively separating the line-synchronizing and trame-synchronizing impulses from each other. Moreover,'with this embodiment of the invention the scanning wave generators of the receiver may include synchronizing circuits which are both adapted to be controlled by syncnronizmg impulses of the same polarity.

In tnis system, the output of the video-irequency oi the ampliiier 43 is connected to the control grid of the cathode-ray tube 44 by way or a coupling condenser 52 and is also coupled to tne generators 45 and 46 by means of rectiiying and separating apparatus indicated generally at b3. 1ne.generators 45 and 4i include synchronizing circuits adapted to be controlled by positive synchronizing impulses. The rectifying means comprises a diode 54 connected across the output of the amplifier 43 through an inductance 55 in series therewith, as shown, and a source of biasing potential, indicated by the battery 5i, a resistor 51 being connected across the diode I4 and inductance 55. The electrical valuesy of the condenser b2 and the resistor 51 are very large and provide a large time constant for the rectiiler. The battery 56 provides an initial negative bias for the c ontrol grid oi the cathode-ray tube to ensure proper operation thereof and also provides a negative bias to the vacuum tubes at the input of geenrators 45 and 46 whereby only the positively poled synchronizing pulses are eilective.

The diode 54 acts as a peak rectifier passing i current only during the synchronizing impulses,

cutting oil the video-frequency components. 'I'he inductance 55 provides a load or output circuit across which are developed synchronizing imtiono!thesystemotlig.2embodying'thepres.

y:'entinvventioratheunitllispcovidedfourthepur- -pose of'deriving the eiiectively separated lineaynchronisingandi'rame-synchronizinghnpulses. lo-thattheymaybe'appliedtothegenerators 4I and ireerrommutual interferenceandforthe pm'poseofstabilisingthesignalinrmttocathode- Y raytubej44. y y

'lhisarrangenentisadaptedforuseinasystemin which the cmnposite modulation lign!! includes combined video-frequency components,

back-graind'illumination components', the latter ontheblack'sideotitszemaxiaandsynchronizing components of'th'e type described 'lhisarrangementprovidesasinglerectiiierand associated load circuit responslveto the amplitudeoandtheslopesoi'theedgesothesyhchronising pulses for simultaneously deriving'ls pulse voltages. The flow ot these impulses or current through the inductance il is effective to develop a voltage, which is the derivative ot the current, across inductance I5, thereby serving effectively to separate the line-synchronizing and frame-synchronizing impulses from each 1.

other. A reversing inductance 58 is coupled to the inductance and the inductance: Ii and Il vare connected `to the synchronizing circuits ot the generators. and 46, respectively.

In the operation o! the system ot Fig. 2, considering a signal of the type described above to have beenreceived and developed in the output circuit ot the ampliiier 4I, the diode passes current onlyduring occurrences of the synchronizing impulses as stated above. this being determined by the large time constant circuit comprising the condenser i! and the resistor Il and the initial bias provided by the battery It. Hence, during each of the synchronizing impulses, current ilows through the inductance' element II in series with the diode and there are developed across this element synchronizing therethrough so that a. periodic voltage wave is developed thcreacross comprising A impulses the form oi which is dependent upon the wave forms o! the applied impulses, particularly the relative slopes'oftheleadingandtrailingedgeaotthe synchronizingimpulses. Since'thesignalcomthantheir leading edges. The synchronizing components developed by differentiation across the inductance element Si are of the form of double impulses,- one-half of each double impulse being a relatively narrow pulse oi substan- 6 tial amplitude and the other half being oi inappreciable amplitude. 'Moreover, since the corresponding diflferences in slope of the line-synchronizing and field-synchronizing impulses are opposite 'in sense, the resultant line-synchronizing l0 and: frame-synchronizing pulses oi substantial amplitude are of the opposite polarity. The inductance 5 8 being coupled to the inductance il to provide a reversal of polarity, the voltage across the inductance 5l may be applied di` l5 rectly to the synchronizing circuit o! the linetrequency generator 45. This is possible since the line impulses thus developed, which are oi appreciable amplitude, are then positively poled as applied to generator IS. The frame pulses 20 level of the signal as applied to the tube. Thediode derives from the signal output o! the am- 30 pliiier I! a positive unidirectional voltage equal to the peak value of the composite modulationsignal on the black side oi its zero airis, this voltage appearing across the resistor il and being applied to the control grid of the cathode-ray tube m op- 8'5 position to the initial ilxednegative bias ot the battery 56 to control only the background illumination of the image reproduced by the system. The resultant video-frequency signal applied to ananas and frame frequencies may be, as has 'been stated, 13,230 and 60 cycles, respectively.- After the line-synchronizing and frame-synchronizing impulses have been combined in the mixing ampliiler ll and have been further combined in the amplifier -20 with the video-frequency signals, the combined signal appearing in the output circuit of the amplifier 20 is of a form such as shown by the curves of Figs. 6 and 7, where again the two curves represent the signal as it appears during alternate held-scanning cycles, the backgroundillumination component oi the signal being represented by the peak value of the signal in the black direction. In Fig, 6 there is indicated by the letters w, b and s, the respective signal levels representing white, black, and the peak amplitude of the synchronizing impulses in the black direction. Since this signal, as shown, is applied tothe carrier wave as modulation, it will be apparent that increases in the amplitude of the carrier correspond to increases in illumination of the image, while the synchronizing impulses are all represented by decreases in carrier amplitude.

25 The curves oi Figs. 6 and 'I also represent the wave forms of the signals developed in the out-'- put circuit oi.' the amplifier 43 of the receiver of Fig. 2. 'The video-frequency portions of the curves being removed, as explained above, by virtue of the biasing of the diode 54 in the system oi' Fig. 2, the synchronizing signal voltages and resultant currents through the inductance element 55 are, therefore. of the form shown by the lower portions b-s of these curves. Since these currents are diilerentiated by the inductance element 55, the resultant voltages developed acrossthis element is'of the forms shown by the curves oi' Figs. 8 'and 9 where, as explained above, the only pulses of each resultant double the control grid, therefore. is of a desired wave 0 impulse of the respective line-synchronizing and iorm which includes the unidirectional and lowfrequency background components'as well as the y video-frequency picture components oi the signal.

be readily explained by reference to the curves of Figs. '3-9, inclusive, which' illustrate the wave forms oi' waves developed at various points in the systems oi Figs. land 2, time being represented by abscissae and relative amplitude by ordinates 5 in each instance. lThe curve of Fig. 3 represents the wave form of the frame-synchronizing impulse wave developed in the output circuit oi the limiter l! in thesystem of Fig. l. For simplicity,

an synchronizing impulses are shown in Figs. a-v, 55 inclusive, with negative polarity. It will be noted that the impulse o! this curve is characterized by a leading edge oi relatively gradual slope and a trailing edge ot relatively steep slope. The curves of Figs. 4 and 5 represent the wave forms ot the 00 periodic line-synchronizing impulses, developed in the output circuit of the limiter and amplifier 2l, as they appear duringgalternate iield-scanning cycles, that is, during the intervals when the held-synchronizing pulse occurs.' The unique 05 feature of the line-synchronizing impulses is that their leading edges have relatively steep slopes and their trailing edges have relatively lesser slopes, vitgthus being seen that the line-synchromung and neid-synchroniserg4 impulses have 7 leading and trailing edges of a predetermined diierence in slope, the corresponding diiierences in :loro of the line-synchronizing and nels-synchronizingimpulsesbeinginoppositesenses. In,

a preferred arrangement. for example, the liii e.

frame-synchronizing components of appreciable amplitude are oi opposite polarity. l

While there have been described what are at present considered to be the preferred embodi- The general operation oi the entire system may 45 ments of this invention, it will be obvious to those skilled in the art that various changes and modiilcations may be made therein without departing-from the invention, and it is, therefore, 'aimed in the appended claims to cover all such changes and modiilcations as fall within the true spirit and scope of the invention.

What is claimed is:

l. A television system tor receiving and reproducing a video-frequency signal including combined video-frequency components, backgroundillumination components. and synchronizing components including line-synchronizing andl neldsynchronizing impulses having amplitude values outside the amplitude range of the videofrequency components, comprising a single rectiiier and associated load circuit for simultaneously deriving from said signal a unidirectional bias voltage representative oi background illumination, and effectively separating the line-synchronizing and held-synchronizing impulses from each other, means for utilizing said etl'ectively separated synchronizing impulses for synchronizing separate scanning operations of the system, and means responsive to said bias voltage for controlling only the background illumination of the image reproduced by the system.

2. A television system for receiving and reproducing a vvideo-frequency signal including combined video-frequency components, background-illumination components, and synchro- I nizing components including line-synchronizing and nem-synchronizing impulses having amplitude values outside the amplitude range ofthe l video-frequency components and'having leading and trailing edges of a predetermined diierence in slope, the corresponding diierences in slope o! said line-synchronizing and eld-synchronizlng impulses being in opposite sense, comprising V'a single rectiiler and associated load circuit and responsive to the amplitude of, and to the slopes of tbe-edges o f, said synchronizing impulses for simultaneously deriving from said signal a unidirectional bias voltage representative of backgroamd illumination. and line-synchronizing and ddd-synchronizing impulses eirectiveiy separated from each other, means for utilizing said effectively separated synchronizing impulses for synchronizing separate scanning operations of the system, and means responsive to said bias voltage for controlling only the background illuminatlon of the image reproduced by the 3. A television system for receiving and re'- producing a video-frequency signal including combined video-frequency components and synchronizing components including line-synchronizing and Bold-synchronizing impulses having amplitude values outside the amplitude range of proportional to said peak value o! said signal. and responsive to the slopes of the edges of said Synchronizing impulses for developing from said signai impulses corresponding to said line-synchronizing and frame-synchronizing' components etiectively separated from each other. means 'for utilising said synchronizing impulses tor synchronizing separate scanning operations of the system. and means for utilizing said bias voltage.

for continuing only the background-uniminstion Aoi the image reproduced by the system.

' diode rectifier for deriving vfrom said signal a said video-frequency components having leading and trailing edges of a predetermined diilerence in slope, the corresponding diierences in slope of said line-synchronizing and held-synchronizing impulses being in opposite senses, the background-illumination being represented by the peak value of the signal in the black direction, comprising a single rectiiying means and associ- 4ated loadcircuit forderivingi'romsaidsignal a, background-illumination control-bias voltage.

bias voltage proportional to said peak value oi' said signal. an inductance element in circuit with said rectiner for deriving from said signal linesynchronising and mld-synchronizing impulses effectively separated from each other, means for utilizing said eneiveiy separated synchronizing impulses for synchronizing the separate scanning operations of the system, and means responsive jointly to both said bias voltages for controlling only the' backgroimd-illumination of the image reproduced by the system.

CERTEICATE oF CORRECTION.

' I Ju'ly 15, 19141.

'-HARoInmLEws.

. 1s h'ereb'yfeertified that error appears`in lthe above numbered petent Y corretion as fol-lows In the drawing, strike out Sheet 5 contaihis Fis. 5; 11:11:11@ heading'xo sheets 1 and 2, for' "A sheets" read '5 Sheetsa-f intheheading tothe lat sheet of drawing, for ."h. Sheets- Sheet 1|." reali-f5 Sheets-Sheet 5pm; and for thefigures -now numbered 1+, 5,-

6, 7,. 8, 9,:ad-10 rfead5 11,' 5; 6, Y, 8, and9 respectively; in the printed 'speeifictionQ page 5`, eeond4 column ,line 55 fo/z` raidly re'ad-rapidly-- Y pega l).l., senon-d collmn, line 5l', for geenrators read -'generatorsf; and

' -that the 'ad Lettera Patent should .he read with this correction therein that the`ame mgylcoform tothe re'rdof the case in the Patent Office.

s1gneq angsealed m1550111 day of september, A.. D. 19111.'

Henry van Arsdale, l (Seal) Y Acting Commissioner of Patents.

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