US2302425A - Television apparatus - Google Patents

Television apparatus Download PDF

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Publication number
US2302425A
US2302425A US363021A US36302140A US2302425A US 2302425 A US2302425 A US 2302425A US 363021 A US363021 A US 363021A US 36302140 A US36302140 A US 36302140A US 2302425 A US2302425 A US 2302425A
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United States
Prior art keywords
amplifier
components
resistor
signals
circuit
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Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
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US363021A
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English (en)
Inventor
Franklin M Deerhake
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General Electric Co
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General Electric Co
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Filing date
Publication date
Priority to FR959967D priority Critical patent/FR959967A/fr
Priority to BE479144D priority patent/BE479144A/xx
Application filed by General Electric Co filed Critical General Electric Co
Priority to US363021A priority patent/US2302425A/en
Application granted granted Critical
Publication of US2302425A publication Critical patent/US2302425A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/16—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N5/00—Details of television systems
    • H04N5/14—Picture signal circuitry for video frequency region
    • H04N5/16—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level
    • H04N5/165—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level to maintain the black level constant

Definitions

  • My invention relates to television apparatus, and in mrticular to apparatus for reinserting, at the output a video amplifier, low frequency and set current components of video signals transmission than-black region.
  • an image to be tratted is usually scanned in a series of lines, and electrical signals are developed which are representative of the brightness of -each elemental picture component of the image.
  • These signals mint, in general, convey two kinds of information: first, the relative brightness oi'the picture elements, determined by the details 0! the image, and second, the average absolute ing to the absolute monly designated as the infra-black or blacker- Since the fixed level 0! the pedestal portions of the video signal corresponds to black in thepicture image, it provides a very convenient reierence level to which may be referred the instantaneous picture signal intensity, correspondments of image.
  • the sigmust represent both instantaneous and steady state conditions and contain a wide range or frequency components down to and including following specification, ii a video amplifier is capable oi transmitting, without substantial distortion, the wave form oi the pedestal portions and allbut the lowest frequency components or the picture signal portions, a peak rectifier cirt current components. -All these components must be present in the final signals which are utilized in they receiving apparatus to reproduce the image, if distortion is to be c uencies and direct currents, as'well as higher frequencies extending over the wide range of frequencies present in television video signals, are
  • the synchronizing pulses which comprises impulses of greater amplitude superimposed on the pedestals and extending into the region comvideo signal is one in which increases in signal amplitude are reprecuit coupled to the amplifier output may be utiheed to develop signals substantially proportional to the non-transmitted low irequency and direct current components. These may then be mixed with the amplifier output and supplied to a utilizationcircuit. usually a final video amplifier or a modulator.
  • the types of amplifier and modulator tubes which are now available for television service require a low impedance input circult for stable operation.
  • the rectifier output must inherently be 0! high' impedance and the problem is presented of coupling it directly to the utilization circuit without causing circuit instability.
  • the reinserted components must bear the proper amplitude relationships to the transmitted Si nal components.
  • FIG. l diagrammatically represents portions 0! a television apparatus embodying-my invention
  • Figs. 2a through 2d are representative oi the wave i'orms oi video-signals which will be referred to for a better understanding of the operation of my invention.
  • Whlleths video amplifier ill or 1 has been illustrated as a single stage, it will he observed that it may comprise a-plurallty oi stages each of which may be similar to the one just described.
  • a rectifier l8 illustrated as a duo-diode having its cathode electrodes and anode electrodes respectively connected together to function as a single diode rectifier.
  • the cathodes of the rectifier is are connected to the anode of the video amplifier ill through a capacitor 2d and the anodes are connected to the cathode oi the amplifier it through a bypass capacitor ill.
  • the anodes are also connected to a movable tap-23 on a bias potentiometer ii.
  • the potentiometer H is connected across a suitable source of potential, indicated by the terminals 22 and i8, which is oled to maintain the right-hand end of the potentiometer negative.
  • the unidirectional potential of the anodesof the rectifier HQ with respect to ground may be adjusted by adjusting the movable tap of the shunt type for rectifying the'slgnals ap The peering in the output or" the amplifier id.
  • the resistor is also included in the grit ircuit of a triode amplifier This amplifier is connected in a cathode-coupled circuit, sometimes called a cathode-follower circuit.
  • the anode'oi the amplmer 25 is connected directly to the positive terminal ll of the source of anode potential and the cathode thereof is connected to the grounded terminal ill of this source through resistors 26 and 27 and the potentiometer ii.
  • the grid is connected directly to th upper ter mluul of the load resistor 26.
  • the amplifier When operated in this fashion the amplifier has a gain somewhat less than unity, which is practically constant for relatively lowfrequencles down to and including unidirectional components.
  • the gain is always less than unity but it can be made very nearly equal to unity by using a high gain amplifier.
  • this circuit permits stable operation with a relatively high value of resistance in its grid circuit and low resistance in its common cathode circuit.
  • the resistor 21 is connected across the termlnals of a suitable utilization circuit. As illus trated, it is connected between the grid and cathode of a tetrode 28 through the bias potentiometer 28.
  • the tetrode 28 and associated circuits may constitute 21 final power amplifier for the video signal; or, in a. television transmitter, it may comprise a modulator stage.
  • a portion of the video signal output of the amplifier as, appearing across the load circuit elements l4, l5 and i6, is also coupled to the grid of the amplifier 28 through the capacitor 29.
  • the video signal including the picture signal portions 39 and also the pedestal and synchronizing portions 4
  • the pedestal portions ii of the signal assume a reference level corresponding to blacliin the pic ture image. This level is indicated by line 32.
  • the synchronizing pulses extend. a defimte distance above this level into the infra black region.
  • the direct current component of the video signal during the interval represented is proportional to the distance between the axes tit and ii.
  • the ped-. estals ti and synchronizing pulses d3 lie on the some threshold level 42 as before.
  • the pedestal portions must establish components will necessarily be attenuated or lost in transmission through the capacitor 52.
  • the signals of Fig. 2a and Fig, 2?) will appear on the grid of amplifier to generally as represented in Figs. 2c and 2cZ,-respectlvely. 1f
  • the capacitor i2 is large enough, the wave forms of the pedestals M, the synchronizing pulses 33 and the picture signal as will be preserved, but the signal will be referred to the arbitrary alternating current axis so such that the areas of the video signal above and below this axis are su'ostantlally equal.
  • this axis has no relation to the background illumination age level so of the stout of the capacitor and resistor 24 is mode long relative to the interval between adjacent pedestals. Therefore, through detector action as fixed reference level 44 for the rectified signed is established Just slightly below the tips of the synchronizing pulses.
  • resistor 24 Therecrifled potentials appearing on resistor 24 correspond to the distance from this level to the avervideo signals.- The slight difierence between this new reference level and the level of the blorimhg estsls is nearly constant since the height of the synchronizing pulses is is easily eliminated by a sim pie adjustment of other portions of the reinsercoustent, and this tiou circuits now to be described.
  • time constout of cspscltor 2d and resistor 2d should be long enough to permit rectification of the peaks oi the synchronizing pulses, it should not be too long. Otherwise, variations in the intensity of the background illution will not be ialthfully reproduced. As at rough criterion the time constout should be short relative to the time inreuuired to scam one complete picture image. 1
  • the potentiometer 2i periorms several important functions. in. the first piece, by reason of the potehtied drop across the portion of this potentiometer to the right of the top 2%, e small current how is meintoined through the diode i8 and resistor t8 This provides an initial bias on the diode is which insures linearity of operation even in the presence oi very weak signals. In the second piece, the potential drop across the resistor 2 bioses the grid of the amplifier 25, which in turn determines the minimum current flowing through resistors 26 and Ti. Itwill be observed that e.
  • the rectified potentials developed on the resistor 2d are substantially proportional to the components to be reinserted at the grid of ampliher so, it might be assumed that plifier 28 could be directly coupled to this resistor.
  • the resistor 2d will have 9. high resistance of severel'megohms. The in clusion of a high resistance of this order in the grid circuit oi amplifier 28 wouldnot be satisfacefllciency as the higher frequency components of the well-known amplifier 2! from the Il'ld of thecmpliner 28- in order to obtain better high frequency response.
  • this resistance isolates the capacity between the cathode of amplifier and ground from the grid of amplifier 28 and thus reduces attenuation of high frequency currents transmitted through capacity 28 by this cathode to ground capacity.
  • This resistance 26 may be relatively small compared to resistor 21 so that most of the amplifier output appears on the latter resistor.
  • the reinserted low frequency and direct current components developed on resistor 21 have amplitudes somewhat less than they would have bad if transmitted directly through the video amplifier H) with the same the video signal.-
  • the detector is actually establishes a reference level for the rectified signal which differs very slightly net result is that a.
  • the cathode-coupled. amplifier 2! introduces a small amount of desmplification and 9. further loss occurs due to the drop through the decoupling resistor 28.
  • the cathodecoupled amplifier 25 chars on efiective solution to this problem.
  • such it circuit permits stable operation with a. high veins of resistance in its grid circuit and a. relatively low value of resistance in its output circult. It also permits the use of a. smell triode of a. type that is less susceptible to instability than the type of tube required for amplifier do, which will generally be e. power tube.
  • the resistor Ed is employed to decouple the unavoidable shunt capacity of the cathode of the perfect restoration of all video signal components at the inputto amplifier 28 is achieved. Obviously, it can also be made greater or smaller should over-compensation or under-compensation be desired.
  • Resistor l3 ohms Resistor l4 do 1,000 Resistor l6 do 10 Capacitor 28 microfa.rad .01 Resistor 2
  • a source of signal electromotive force having frequencies extending over a band including low frequency and unidirectional components varying with respect to a predetermined signal level, said electromotive force having recurrent portions of an amplitude substantially equal to said level, alternating current translating means for said composite signals, a utilization device having low impedance, and means to reproduce from the output of said translating means currents in said utilization device having said high frequency, low frequency,
  • said path for low frequency components including a peak rectifier having a high impedance load, and a cathode follower amplifier connected between said high impedance load and said low impedance utilization device, the cathode of said cathode follower amplifier oscillating motive force but too*low.
  • a cathode follower am plifier connected between said load and said input impedance tos'upply low frequency and unidirectional components 2mm .said load to said amplifier for amplification, and a separate high frequency path between said source and said input impedance to supply high frequency components of the televised picture to said amplifier for amplification thereby.
  • a source of electromotive force varying in accordance with a televised picture and its background brilliance and having only alternating current components varying with said background brilliance a utilization device, means to supply to said utilization device high frequency current varying in accord with v said televised picture and low frequency and unidirectional currents varying in accord with said background brilliance,' said means comprisin separate paths between said source and said utilization device for said high frequency currents and for said low frequency and unidirectional currents, said low frequency path having a peak rectifier for said alternating electromotive force, a load resistor therefor, and a cathode follower amplifier connected between said load resistance and said utilization device to transmit to said utilization device said low frequency and backforce varying in accord with a televised image and'ithackground brilliance and having only alternating current components, a peak rectifier for said alternating electromotive force having a load resistance on which appears unidirectional electromotive force varying as the low frequency and background components of said telev
  • means for rectifying said amplified components comprising a diode detection circuit having a time constant which is long relative to the longest interval between said' portions, a thermionic amplifier having an output impedance common to its grid and anode circuits, means conductively coupling said detection circuit to said grid circuit, a video signal amplifier having its input circuit conductively coupled to said impedance,

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Picture Signal Circuits (AREA)
US363021A 1940-10-26 1940-10-26 Television apparatus Expired - Lifetime US2302425A (en)

Priority Applications (3)

Application Number Priority Date Filing Date Title
FR959967D FR959967A (en(2012)) 1940-10-26
BE479144D BE479144A (en(2012)) 1940-10-26
US363021A US2302425A (en) 1940-10-26 1940-10-26 Television apparatus

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US363021A US2302425A (en) 1940-10-26 1940-10-26 Television apparatus

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US2302425A true US2302425A (en) 1942-11-17

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2472577A (en) * 1946-05-31 1949-06-07 Rca Corp Double time-constant circuit for direct-current restoration
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2569289A (en) * 1945-08-31 1951-09-25 Rca Corp Automatic gain control system
US2618703A (en) * 1947-12-13 1952-11-18 Hazeltine Research Inc Keyed direct current reinsertion circuit
US2675423A (en) * 1949-07-22 1954-04-13 Hazeltine Research Inc Direct-current restorer system for compensating for the finite impedance of restoring tubes
US2708687A (en) * 1949-05-10 1955-05-17 Motorola Inc Combined direct current reinserter and synchronizing pulse separator
US2953639A (en) * 1955-01-12 1960-09-20 Hell Rudolf Dr Ing Apparatus for automatically adjusting the operation of a facsimile transmitter

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2569289A (en) * 1945-08-31 1951-09-25 Rca Corp Automatic gain control system
US2472577A (en) * 1946-05-31 1949-06-07 Rca Corp Double time-constant circuit for direct-current restoration
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2618703A (en) * 1947-12-13 1952-11-18 Hazeltine Research Inc Keyed direct current reinsertion circuit
US2708687A (en) * 1949-05-10 1955-05-17 Motorola Inc Combined direct current reinserter and synchronizing pulse separator
US2675423A (en) * 1949-07-22 1954-04-13 Hazeltine Research Inc Direct-current restorer system for compensating for the finite impedance of restoring tubes
US2953639A (en) * 1955-01-12 1960-09-20 Hell Rudolf Dr Ing Apparatus for automatically adjusting the operation of a facsimile transmitter

Also Published As

Publication number Publication date
FR959967A (en(2012)) 1950-04-07
BE479144A (en(2012))

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