US2402096A - Control circuit - Google Patents

Description

Annu...

mix

F. J. SOMERS CONTROL CIRCUIT Filed Nov.I 20, 1943 june i1, 194s.`

INVENroR. Frank rl'omer BY nun www

Patented June Il, 1946 CONTROL CIRCUIT Frank J. Somers, Rockville Centre, N. Y., assignor to Radio Corporation of America, a corporation oi Delaware Application November 2o, 1943, serial No. 511,179

appear to icker or Vary in brilliance, and in order that relatively fast moving objects may be satisfactorily reproduced at the television receiver. In such systems, particularly Where high delity and good detail are desired, the band width oi? the transmitted' television signais must be quite wide, and in order to transmit such images without requiring an excessively wide transmission channel, it is common practice to suppress at least a portion of one side band of the modulated carrier. Such systems necessarily require relatively wide lband intermediate frequency amplifying channels and video signal amplifying channels in order that none of the video signals will be attenuated during the transmission.

` In the present system, however, it is contemplated that television be used for transmitting information obtained from a meter or a series of metersior similar information) from one location to another. In the application of tele- Vision to this or similar purposes, it is not necessary that the eld deflection frequency or the line deection frequency be as great as in the transmission of television images for entertainment purposes since the rate -of movement to be observed will not be excessively rapid.

Accordingly, for illustrative purposes, in the present invention the fleld or frame deection frequency has been chosen to be of the order of cycles per second, with the line deflection at approximately 3000 cycles per second. In such a system both side bands are transmitted, with the result that the radio frequency transmission channel occupies approximately 750 kilocycles while' the video band width is approximately 375 kilocycles. Furthermore, in the present system no interlacing is employed, as is usually the case in the transmission of television images for entertainment purposes.

In order that the produced image on the screen or target ofthe image producing television tube will not iiicker an appreciable amount, an image producing tube having a relatively long persistence screen should be used, and by proper choice of an automatic volume control circuit any objectionable flicker may be substantially removed. Inasmuch as theapparatus is to be used near other electrical or mechanical equipment, it is possible that. in some instances, such equipment may introduce radio frequency carrier modulations which would cause objectionable brightness changes on the screen of the television image vproducing tube. The automatic volume control circuit proposedin the present invention is also so designed to eliminate such brightness variations, and is sufliciently eiiective that the television transmitter may be located in an airplane without resulting in any objectionable M changes in, image or `picture brightness at a.

remotely located television receiver.

Since the present invention is to be used for in conventional television used for entertainc ment purposes as is well known tol those skilled in the art, but instead the automatic volume control circuit may be responsive to the entire K video signal envelope which may be considered as including both the rvideo or image signals and the synchronizing signals.

Accordingly, the present invention provides,

after suitable intermediate frequency ampliiil cation, a demodulating `device for producing the y video signal series, this series of signals being subsequently applied to an automatic volume control rectifier where the desired automatic volume control potential is developed. By proper choice of the time constants associated with the automatic volume control circuit, the desired maintenance of signal strength may be accomplished and an image may be produced which is relatively free from any objectionable effects oi' rapid signal strength variations.

It is therefore a purpose of the present invention to provide in a television receiver an automatic volume control circuit which may be effectively used to eliminate the effects of rapid signal Variations in a television system wherein .A relatively low field and line deflection frequencies are employed.

y Another purpose of the present invention relates to an improvement in a television receiver for use in telemetering or similar purposes wherein an automatic volume control circuit is provided which is responsive to the entire video A signal series for producing the desired control action.

Still another purpose of the present invention resides in the provision of an automatic volume control circuit in a television receiver for use in a telemetering or similar service wherein the time constants associated with the automatic volume control are such as will produce the desired results. A

Still other purposes and advantages of the present invention will become more apparent to those skilled in the art from the following detailed description, particularly when considered in connection with the drawing wherein:

The gure shows a preferred form of the present invention.

Referring now to the drawing, the transmitted suitable antenna element I and are impressed upon a radio frequency amplifier I2, An oscillator I4 is also provided and'energy from the" oscillator is supplied to a-mixer tube where these oscillations, voperating in conjunction with the the order of 72.7 megacycles and to operate the' receiver oscillator at 96.2 megacycles. With the choice of these two frequencies, an intermediate frequency carrier of the order of 23,5 megacycles is produced.

The intermediate frequency carrier available from the radio frequency amplifier and mixer I2 is then impressed upon the control electrode of an intermediate frequency ampliiler tube ii which includes, in addition to the control electrode, at least 4a cathode and an anode. 'I'he intermediate Afrequency carrier is applied to the control electrode of tube i8 by way of coupling condenser I8. The cathode of tube II is connectedA to ground' by way of cathode resistance 2l, while the control electrode of the amplifier tube is connected to an automatic volume control conductor The amplified intermediate frequency carrier obtainable from the anode of tube 38 is impressed upon the control electrode of a third intermediate frequency amplifying tube M, the -coupling arrangement between tubes 38 and 5I being similar to the coupling arrangement between tubes it and 38, The control electrode of tube I4, however, as indicated in the drawing, isnot connected to the automatic volume control conductor but instead is connected to ground by way of grid resistor. 'I'he cathode of tube I4 is also consignals from' an appropriate television transmit- Y ter, such as referred to above, are received by 22 by way of grid resistance 2l and isolating resistance 28. A relatively small-condenser 2l is connected between the Junction of these two resistances an'd ground in order to provide an appropriate carrier frequency path.

'I'he anode of tube lS-is connected to positive terminal 3l by way of tunable inductance 32 and resistance 34, these elements being connected in series. The condenser Il is connected between the Junction of these elements and ground.' 'Ihe coupling between the first intermediate frequency amplifier tube Il and the next succeedingintermediate-frequency amplifier tube ll includesin addition, tunable inductancev 40 and couplingy condenser l2, inductance Il being tapped into inductance 32 so as to provides suitable mutual inductance between coils 22 and 40 to obtain` a suitable band-pass transformer characteristic.

The intermediate frequency amplifier tube ll also includes a cathode and an anode. The cathode is connected to grond by way-of resistance 4I, while the anode is connected to positiveterminal 43 by way of tunable inductance 4I and-re-- sistance The control electrode of tube 2l is connected t0 the'automatic volume control conductor 22 by way of series resistances Il and B0, and the junction of these reslstances is connected to ground by way of a relatively small condenser nected to ground by cathode resistor 5l. The anode of tube 54 is connected to positive terminal VBil by tunable inductance 82 and resistance Il. A condenser is connected in parallel with resistance I4 for illtering purposes.

` 'I'he coupling elements between the ilnal inter-mediate frequency amplifying tube Il and a 'demodulator tube 6I are similar to the coupling arrangement used between the preceding stages of intermediate frequency amplification. l

The demodulator comprises a pairv of diodes including cathodes I8 and v1li and anodes 1 2 and 14. The cathode 1I of one diode is connected to the anode 'l2 oi' the other diode, and the ampliiled intermediate frequency carrier is applied to these elementsby way of coupling condenser 1l.'

The cathode .1li and the anodeff|2 are also connected to ground by way oflresistance 1l.

As is well known to those skilled in the art, a conventional television transmitting system for entertainment purposes employs vestigial -side band suppression with the result that one complete set of side bands is transmitted, whereas only ay portion of the other set of side bands is permitted to leave the transmitter. In the pres- -ent system, however, both side bands are transmitted, with the result that the amplified intermediate frequency cafrier envelope is substantially symmetrical a ut an alternating current axis. "i:

Separate load circuits are provided for the two diodes contained within the demodulator Il; the

load circuit for cathode ligand anode Il beingv resistance 80, while the loaii circuit for cathode B8 and anode I2 is inductance 22, resistance element of potentiometer Il and a further series resistances` 88. A relatively large condenserl.

is connected between ground and the-junction of resistance It and potentiometer Il, and the purpose of condenser Il and resistance Il will be explained later.

Since the load circuit associated with cathode is connected between the cathode and ground, the potential of the cathode Il will increase in a positive direction for increases in the intermediate frequency carrier intensity. In the present system, the synchronizing signals are 'transmitted at substantially full carrier intensity,

andthe intensity of the transmitted carrier is decreased or reduced for image signals representing increases in light intensity. This is conventional modulation in television transmitting systems. Accordingly, the potential oi the cathode l will be most positive during synchronizing signal intervals, and the positive potential o! this element willdecrease whenysignslsare trans-r mitted representing white in the picture.

A conductor Il is connected between the Junc-I tion of the inductance I2 and the potentiometer resistance M, and is for the purpose of supplying the demodulated Ivideo signal to the control electrode of synchronizingsignal amplifier tube' 92 which includes a cathode, Va control electrode and an'anode. The .cathode of the tube .lis

connected to ground by way of resistance,

the value of thisfresistance is' so chosen that the amplier` is most eective for signalintensities Vsuch as those developed during synchronizing intervals. The anode of. tube 92 is connected-to positive terminal 96 by way of load resistance 08. The amplified synchronizing signals that-*are f present at the anode of tube 92 extend in aneging` signal. separating-device |00'.

eficaces`v This-element provides a background control for the imageproducing tube.

. The .ampli'ed video signalsas applied to the control electrode of the electron gun structure therefore modulate the current intensity of the developed cathode ray beam to' produce an image on the viewing screen or target of theimage :producing tube |l0I ina manner well known to those iskilledin' the art; p

In orderthat the receiver will be most effectiveto produce television images of substantially constant apparent `light intensity with a minimum oi` flicker, and in order to overcome any unage variations of proper intensity and wave form, .such that when the developed potential variations (or current variations) are applied todeecting coils |00 and |08, the cathode ray beam developed in the Kinescope or image producing device I I Il` will be caused to be deflected in a desired manner and at a' desired rate in synchronism with the deection of the scanning cathode ray beam in thetelevision transmitter.

Demodulated video signals are also obtainable from theA movble contact associated'with the potentiometer 84, and these video signals are ap plied tothe control electrode of video amplifier tube ||2 by way of conductor H4. The potentiometer 84 operates as a contrast control to desired or spurious modulations of the radio frequency carrier by reason of the action of airplane propellers .or similar moving apparatus located adjacent thetransmitter, an appropriate auto- 'inatic volume control circuit must be provided to alter the'gain of thetelevisionreceiver. rilie gain control is preferablyexercised onjat least some of the` intermediate frequency amplifying tubes, and in the particular' circuit shown in Figure 1 'of the drawing, tubes' I6 and, 30 ofthe intermediate frequency channel are subjected to automatic volume control potentials.

For developing the desired automatic volume control potentials, the video signals developed at the anode 14 (across load resistance 00) are utilized. At this diode the video signals have a-polarvary the intensity of the video signals applied to the video amplier tube. tube ||2 includes at least a cathode, a control electrode and an anode,y and the cathode is connected to grund by Way of resistance I5 while the anode is connected to positive4 terminal IIB by-way of loadv resistance H8, peaking induct-v ance |20 and decoupling resistance |22.l -A relativelylarge lter condenser |24 is connected between ground and the junctionof the decoupling resistance |22 and the inductance |20.

The video amplifier.

ity such that the synchronizing signals extend in a negative'direction.

In order' that desirable `automatic volume con!` trol potentials may be developed, an automatic volume control. rectifier tube is provided which includes a 4 cathode v|42 and-an anode |44; The

cathode |42 is connected directly to the anode 1li .of-,one of the demodulator diodes, while the' anode |44 is connectedt'o ground by'way of load rex sis'tance I 46. y The cathode |42 is normally maintained at a positive potential relative to the anode,

- and for maintaining such a potentialdifference, the cathode |42 lis connected to a source of low Amplified video Signals will then be present at the anode of tube H2, and the polarity of thesesignalswill be such that the synchronizing signals extend in a negative direction. These amplified video signals are then applied. 'tothe control electrode Vof the electron 'gun structure |26 contained within the picture reproducing tube 0 by way of coupling condenser |28.

The image producing tube may be a. 'conventional "Kinescope with the secondanode thereof`havng applied to it an appropriate high volttage for imparting the desired velocityto the developed cathode ray beam. The electron gun structure |25- of lthev image producing 'tube includes, in addition to the control electrode, a cathode and a first accelerating anode |30. The rst accelerating anode |30 is connected to positive terminal 132,. and a pair`of resistances |34 and |36 are connectedin seriesbetween positive terminal |32 'and'groun'd. The resistance |36 is preferably the resistance element of a potentiometer and thefmovable contact' of the potentiometer is connected to the control electrode of the electron gun structure by resistance |38.

The cathodeof the electron gun structure is voltage positive potential (such as, for example, l2 volts) by way of resistance I 48. With the cathode |42 normal-ly maintained at a positive potential with respect to the anode |44, the automatic volume control rectier tube |40 is rendered non-conductive.

'As statedabove, however, the potential of the video signals developed at the anode 'Ill of one of the demodulatorvdiodes is such that the synchro- `nizing 'signals extendina negative direction, and

. when the' intensity of thesynchronizing signals connected to the junction of resistances I 3 4 and 'y |36. By this arrangement the control electrode of the electron gun structure is `maintained at an average negative potential with'. respect to the cathode, the degree of potential difference der] pending upon the ad'lustment'of the vmovable contact along the potentiometer resistance |38.

or of the image signals is in excess oi the bias voltage applied to the cathode ofthe automatic volume control rectifier tube |40, the cathode will be driven negative with respect'to the anode |64.

`'I'he rectifier |40 is then rendered conductive, and

current is permitted to pass through the `resistance |46 with the result that a negative potential is developed at the anode I 44 of the rectifier tube. The intensity of this negative potential depends upon-theintensity of the videosignals applied to the cathode |42 in anegative direction in excess of the |49. If the received signals are ofrelative1y low in normal bias potentiallapplied to terminal tensity, itis possible that the intensity of the video signals as applied to the automatic volume control rectier may not at any time exceed the positive biasapplied, to the cathode |142. and under such. circumstances no1 automatic volune control potential' will bey developed across resistan'e I 4G.

By reason of the Vapplication of the positive potential to the cathode' |42. a delayed automatic' volumel control action will result, and accordingly" y the television receiver willv operate at' full gain. i

If, however, the received signalsV increase in .i the three intermediate frequencyV tubes, butif desirable or necessary, this action intensity,.then the .biasipotential applied to the,

automatic' volume control tube, M0 y may be exceeded at various intervals, and particularly during the intervals of synchronization, since the the bias'potential appliedto the'automat'ic volunie control rectifier tubevmay be exceeded for 'an appreciable portion of each line ldeflection Ithas been'founcl that for-best operation off `the receiver, the automatic volume-control action should befrelatively rapid and-should be responsive to relatively sudden increase in lreceiver carrier intensity. Filter .condenser I 50 is connected in parallel with the load resistance |46 to provide a slight filtering action, .but-,the size of -`this con'- Ldenser is relatively small in order to afford the desired: rapid automatic volume control action. A resistance |52 isconnected between the anode i |44 and the automatic volume control' conductor 22 for isolation purposes, and in order to illterout any undesired fluctuations-:that may be in-.

With the arrangement as above described; and when the time constant of :theautomaticvolume control circuit (resistance :I O and condenser I 50) is made relatively short, ecbepteme television im-q ages may beproduced` at ltheirnafge producing tube which are substantially free from objectiony'able flicker or pulsation due tolthe low deection` lrate or due vto -any disturbing influence intermediate the transmitter andthe receiver; v Thevfast actingI automatic volume-control ac-l tion, however., results'4 in aV degeneration of thelower videoirequencies as well as the vertical carrier'istransmitted at full intensity during these lintervals. Should anexceedingly strong radio frequency signal be received, it is possible that frequency input ampliier.

sacaban may also be applied, i0 e11- ef the intermedia frequency amplifying tubes', and to .the4 radio It is preferable that the tubes used the inmediate frequency amplifier be of the screen slidvariable mu remote cut-olf type in ordenthiitthe" sired. When such tubes are used, the suppressor f electrode is normally connectedv to ground w iirlf i i1e. gy the screen electrode lhas applied theretol a.` tential somewhat less than the potential applied to the anode, and, as indicated in the-nauw.

reduced poientiai is obtained by', 'a voitegedropg across `a screen grid resistor v.and ,the potential of they screen grid is held substantially constantby use ofvailtering condenser. In most applications it will not be'-necessary-- transmitters, a tuning arrangement-inthe radio frequency amplifier .and in theoscillator could,

conveniently be applied.

r the band of frequencies to be -amplied and thcff 40 particular frequency of the intermediate fre-i" bianking and synchronizing/signals. Iihesvbeen.

found,"l however,A that the lowy frequencies 'couldV be eifectively and'satlsfactorily restored and syn-v chronization improved by means of,l a low boost" ycircuit associated with the demodulator diode usedy for supplying video and synchronizing'sig'nals to tubes and H2. Resistance 8B and condenser 88 are therefore included in the circuit. and -if the condenser 88 is made relatively large, a potential l variation may be produced across vthefresistance I0 which'will assist in ,inereasing the rvoltage variations in the .low frequency end -of the imagefslgnal. frequency spectrum` If further accentuation of the low frequenciesisr desired, this could undoubtedlyibe accomplished `by providing a` fast direct current component inserter orcliitxnpcirf.v

' cuit in the receiver, or by the inclusion offan vfor the particular frequencies employed.; r

claim as new and desire Letters Patent is: f l. A television receiver for receiving@ video n signal modulated radio frequency carrier including a carrierampli'er channel for increasing the amplitude of the received signals, means .todcf It is immaterial what vfil/'pe image producingyy. tube-'is used, i and although' electromagnetic dei-*"-` y iiection is shown in the drawing, it vis to. be un' derstood that either electromagneticor electro.` i static deilection may be used, or acombination-x lof such deflections.

The particular type coupling used lb etyiveen in--` .termediate frequency amplifying tubes isr more j or less immaterial insofar as the'presentinvention is concerned, and the choice of thecoupling circuit and transformers used will depend `.upon

quency carrier. 'I'hose ,shownj and 'descrlbedwdi herein have been foundy satisfactory,`how ever."

'Various alterationsand modifications may made in the present invention without-departing from the spirit and scopethereof, and'itis de sired that any and allfsuch alterations andmodi'' -ncations be considered within the purview or4V -th`e present invention, except as limitedby hereinafter appended claims.

Having new described my inveniion, wiiet I to have protected blt;-y

i ,I y:modulate the amplified signals to' produces videox,I .arrangement foraccentuatlng the low frequencies simL a diode rectifier including a cathode and mrgmmtr before mfdulatmn and' tla'nsf 00 anv anode, means for normally maintaining .the cathode positive with respect :to itsassociated :A anode.- means for applying thep'rodi'ice'cl. video.=f" `4 signal to the cathode ofr said diodewhereby sigi ume control are overcome, 'and as a result a satgg'rlxsdgtigxnce te tildifo pgfi wmlmml www, mddmable television imaged-is prof lnegative control potentia'iat theanodeitheeo; dweilen uw Viewing am@ .f the .m'fpm' e' surname-constant mier associated-with the ducmg tube 'In' n anode of-s'aid diode, means for applying the lpro From .the descriptionof the. circuit-,arrange. duced negative control potential to the met.. 11181158110 in the nlirei'thrmtemediatgf' `1o amplifying channel io eontroitne gam-thereof.; quency' amplifying tubes-areispecifically Areferred 'means .taapply mg produced'vide-o @M .tg to, although it is to be understoodthat a greater television., imagd producing device' and or lesser number 'of tubes may beused; Furtherassociated with mi@ last-name@ means farma; more, .aSShOWn in the figure, y the autOmat centuating the low frequency component of volume control potentials are applied t0 two 0i 76 video signal to compensate foi-'the attenuation et s the "iowtoostf ySii-cuitiii mended,- as described'above,the undesired-effects on the low.

frequencies producedby `the fastautomaticvoli such component by reason` of the controlled variation in the gain. of the amplifier channel and modulate the amplified signals to produce a video signal, a rectifier, means for normally biasing the rectier against conduction, means for applying the produced video signal to said rectifier Whereby signals in excess of the bias potential will cause conduction of the rectifier to produce a varying negative control potential, a short time constant filter associated with said rectifier, means for applying the varying negative control potential to the carrier amplifying channel to alter the gain thereof, means to apply the produced video signal to a television image producing device, and means associated with said last'named means for accentuating the low frequency component of the video signal to compensate for the attenuation of such component by reason of the short time constant filter land the controlled alteration in the gain of the ampliiier channel.

Y '3.'A television receiver wherein relatively low frequency horizontal and vertical deiiection frequencies are employed comprising an intermediate frequency carrier amplifying channel for in-` creasing the intensity of the received signals, means to demodulate the intermediate frequency carrier to produce a video signal series, means to rectify the video signal series 'to generate a direct current potential having a value determined by the intensity of the video signal in excess of a predetermined value, means to apply the generated direct current potential to the intermediate frequency amplifier to control the gain thereof, a short time constant lter associated with the rectifying means, a second demodulator having a load circuit for producing a second video signal series, and means for applying said second video signal series to an image producing device, 'said load circuit and said last namedmeans includ-l ing circuit elements for accentuating the low fre quency component of the second video signal series to compensate for the attenuation of such v carrier to produce a video signal series, means to rectify the video signal series to generate a varying direct current potential having a value deterlmined by theiintensity of the video signal, means to apply the varying direct current potential tol theintermediate frequency amplifier to control the gain thereof, a short time constant filter associated with the rectifying means, a second demodulator responsive to said intermediate frequency carrier for producing a second video signal series, and means for applying the second video signal series to an image producing device, said last named means including circuit elements for accentua the low frequency component of the second video signal series to compensate for the attenuation of such components due to the fast automatic gain control action.

4 i0 5. A television receiver comprising a signal carrier amplifying. channel for increasing the intensity of the received signals, means to demodulate the signal carrier to produce a video signal series, means to rectify the produced video Asignal series to generate a variable direct current potential having a value determined by the intensity of the video signal, means to apply the variable direct current potential to the amplifier to vary the gain thereof, a low capacity electron storage element associated with the rectifying means, a second demodulator responsive to the signal carrier to produce a second video signal series, and means for applying the second video signal series to an image producing device, said last named means including circuit elements for accentuating the low frequency component of the second video signal series to compensate for the attenuation of such components due to the relatively rapid variations in gain control action produced by the variable direct current potential.

carrier amplifier havingv a plurality of discharge tubes, means to apply the amplified video signal carrier to a pair of demodulating elements to produce two separate series of video signals. means to rectify one of the produced series of video signals to generate an automatic Volume control potential having a value determined by the intensity of the video signals in excess of a predetermined value, a short time constant filter associated with the automatic volume control circuit, means to apply the automatic volume control potential to the video signal carrier amplifier to control the gain thereof, and means to apply the other video signal series to an image producing tube, said last named means including elements to accentuate thelow frequency components of the said other video signal series thereby to compensate for the attenuation of such components due to the fast acting automatic volume contro1 action whereby a `visual image of substantially constant average light intensity may be produced on the image vproducing tube.

A television receiver including a video signal carrier amplifier having a plurality of discharge tubes, means to apply a video signal carrier amplified thereby to a pair of demodulating elements to produce two separate series of video signals, means to rectify one of the produced series of video signalsto generate an automatic volume control potential having a value,deter mined bythe intensity of the video signals, a short time constant filter associated with the automatic volumecontrol circuit for decreasing the rate of change of the generated control potential, means to apply the automatic volume control potential to the video signal carrier amplier to control the gain thereof, and means to apply the other video signal series to an image constant light intensity may be produced on'the.

image producing tube. 4 FRANK J. SOMERS.

6. A television receiver including a video Signatv

Images