US2396865A - Signal-generating system - Google Patents

Signal-generating system Download PDF

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US2396865A
US2396865A US481104A US48110443A US2396865A US 2396865 A US2396865 A US 2396865A US 481104 A US481104 A US 481104A US 48110443 A US48110443 A US 48110443A US 2396865 A US2396865 A US 2396865A
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signal
frequency
components
tube
target electrode
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English (en)
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Arthur V Loughren
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BAE Systems Aerospace Inc
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Hazeltine Corp
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Priority to BE470877D priority Critical patent/BE470877A/xx
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Priority to US481104A priority patent/US2396865A/en
Priority to GB5846/44A priority patent/GB579600A/en
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
    • H04N23/40—Circuit details for pick-up tubes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J29/00—Details of cathode-ray tubes or of electron-beam tubes of the types covered by group H01J31/00
    • H01J29/02—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof
    • H01J29/021—Electrodes; Screens; Mounting, supporting, spacing or insulating thereof arrangements for eliminating interferences in the tube

Definitions

  • This invention relates to signal-generating systems and is particularly directed to the reduction oi undesirable shading signals which are genery ally produced along with the desired signal components in those generating systems that utilize a camera tube as the signal generator. While the invention has a wide range of application, it is especially ysuited to television signal-generating systems, and in the description which follows, its apllication to suh ay system is described indeta In ay television signalvgenerating system oi the type under consideration, the camera tube may comprisea cathode-ray tube having a photosensitivemosaic target electrode, an electron gun for developing, accelerating and focusing anelectron beam on the target electrode, and means for scanning the target with the beam duringsuccessive scanning intervals.
  • an optical system establishes a charge distribution on the target electrode in accordance with an image to be translated so that during the scanning operation video-frequency signal components corresponding to the image are produced in the output circuit of the tube. It has been lfound, however, that undesired spurious signals, commonly referred to as' shading components; are v also produced duringthe scanning operation along' with the desired video-frequency signal components. If suchspuriQuS Signals ,arenas-remi wed. they' causellndesrblefshading in the reprbdug' ',fimage, n Y. p
  • the shading signal has compo- -nents which correspond infrequen'cy to the scan'- ning frequencies. It has been proposed, there,-
  • the scanning 4spot must be ofy neness comparable, nottdthe'tele'v'ision image structure..but to the 45; structure er the une raster. Present techniques where this requirement can be readily met so ⁇ that such arrangements have limited'practical value.
  • the ⁇ joutput signal consists of video-ffre-.xv quency-signalecomponents and shading compov nents'butwhenthe beam is incident upon anvjun-"z signalconv- Means are provided-@for deriving as e useful-signal rthe difev ference' between the signals obtained when scanthefvunexposed elementary v areas.Y While.
  • Fig. 1 is a circuit diagram, partly schematic.. of a complete television signal-generating .and transmittingl system embodying the present. invention: Figs. 2 to 7, inclusive, comprise curves used as an aid generating system of Fig. 1; Fig. 8 is a circuit diagram of a modification of a portion of the system of Fig. 1; and Fig.
  • the television signal-generating and transmitting system illustrated comprises a cathode-ray signal-generating tube I5 having a photosensitive mosaic target electrode i6, a
  • the system includes additional means for periodically and substantially decreasing the current of the beam from a predetermined value during the scanning interval at a frequency which is at least as high nal component generated, and frequency-responsive means coupled to the tube having a frequency characteristic related .to the frequency at which the beam current is decreased for deriving a signal which includes the desired signal components and which is substantially free of undesired shading components.
  • the beam current of-a cathode-ray type signal-generating tube is periodically interrupted during the scanning of the target electrode, the interruption frequency being high compared with the highest video-frequency signal component generated.
  • the signal produced in thetube includes both desired video-frequency signal components and undesired shading components.
  • the signal produced comprises only undesired shading components.
  • Stabilizing means coupled tothe output circuit of the tube derive a signal which effectively comprises the diii'erence between the signals produced when the beam is incident upon the target electrode and when the beam is interrupted. Consequently, ⁇ the derived signal includes the desired video-frequency signal y components andis substantially free of the undesired shading components.
  • means including a band-pass lter are coupled to the output circuit of the cathode-ray signal-generating tube for deriving therefrom a signal which includes desired video -i'requency signal components and which is substantially free ofundesired shading components.
  • a signal which includes desired video -i'requency signal components and which is substantially free ofundesired shading components.
  • source of beam current including anlelectron gun structure as well as focusing and accelerating electrodes lto which suitable operating potentials are supplied from a source Il, beam-deiiecting elements I8, AI8 and an output circuit including a load impedance 20.
  • An optical means I4 is provided for establishing a charge distribution on the target electrode in accordance with an image to be transmitted.
  • Deilecting voltages of saw-tooth wave form are supplied to deflecting elements I8, I9 from outputcircuits oi' a. linescanning generator 21 and a field-scanning generator 28, respectively, to cause the beam of signal-generating tube l5 to scan the target electrode in a series of elds oi parallel lines.
  • Blockout voltagesv are supplied from generator 28 through a blocking condenser 60 to a control electrode 38 of tube l5 to suppress the beam during retrace scanning intervals.
  • Output circuits of generators 21, 28, 28 are coupled to combining amplifier 2l to supply thereto synchronizing signals and block-'out signals for transmissionwith the radiated carrier wave.
  • These generators are synchronized by timing pulses from timing-impulse generator -30 which is preferably stabilized by means of a connection 3i to a suitable source of periodic voltage, for example,v to the powersupply circuit or to the synchronizing-voltage source of motion picture mechanism where such is employed.
  • a high-frequency generator 22 of conventional design produces a control potential whicn isapplied tothe control electrode of tube i5 for a purpose to be described more fully hereinafter.
  • thev system Ajust described comprises the elements of a television signal-generating and transmitting'system of conventional design and, since the various elements I4 to 2i, inclusive, thereof may be of any well-known construction, a detailed description ot the general systemand its operation is unnecessary. Brie'ily, however, the image of a.
  • the amplied composite signal is supplied to modulator 22 where itis so impressed upon the carrier wave generated by oscillator 23 as to develop a modulated-carrier i signal.
  • This signal is delivered to power amplier 24 for amplification therein and is thereafter impressed upon antenna system 25, 25 to be radiated.
  • the signal appearing acrossvload impedance 20 of signal generator I when the generator is utilized in a conventional television signal-transmitting system of the type just described will be considered now more particularly.
  • the curve of Fig. 4 representsthe variations in beam currentduring thel scanning'interval in response to .this-control potential.A ⁇ It will be seen that the beam current is periodically 1 video-frequency signal components and undeelectrode i6 acquire charges dependent upon the varying values of light in the corresponding elemental areas of the image focused thereon by the optical system M.
  • the curve of Fig. 2 is assumed to represent such a charge distribution for a portion of a single scanning line on the target electrode.
  • rzero value of charge represents the white level inthe image focused on the target and a charge value of -Ci vrepresents the black level in that image.
  • the polarities of the ordinate axis have been assigned in a manner opposite to conventional practice in order to facilitate a comparison of the charge-distribution curve with curves, to be discussed hereinafter, representing the generated signal.
  • the signal produced across load impedance 20 'under the assumed condition may be as represented by the curve of Fig. 3.
  • a comparivson of this curve with that of Fig. 2 shows that the undesired shading components are represented by the general slope of the curve of Fig. 3. If this slope is reduced to substantially zero value, the undesired shading components are removed and the resultant signal contains only the desired video-frequency signal components.
  • This unit comprises a videofrequency amplifier 38 having an input circuit coupled across load impedance 20 and an output circuit to which is connected a signal-stabilizing means-including Y a diode rectumbler 35, coupling condenser 36and' load resistor 31.
  • Amplier 34 is selected -to have a .substantially flat frequency-response characteristic for a range of frequencies including. the desired' video-frequency componentsI shading l components, and interruption-frequency compresent invention, through the addition oli-units '32 and 33 to the generating system.
  • Unit 32 comprises means for periodically and I ysubstantially decreasing the current of the beam in vgenerator l5 ⁇ from a predetermined, value, or
  • this unit 'delivers to control grid 38- of generator l5 a control potential havinga substantially rectangular pulse waveform and of such value that the beam current of the -ger'i- -erator is periodically interrupted Aeluring the' scanning of each line of the target electrode; Also, it is preferred that the frequency of interl ponents so that the signal from generator l5 vmay be translated .therethrough without distortion. Further, in order to ystabilize this signal,
  • the values of condenser 36 and resistor 31 are so chosen as to give the signal-stabilizing means a time constant which is long'compared with the period of vinterruption of the beam current and short compared with the line-scanning period of the signal generator.
  • unit 33 comprises frequency-responsive means coupled to tube IB having a frequency characteristic related to the frequency at which the beam current is decreased or interrupted for deriving a signal which induces the desired signal compo-r nents and which is substantially free Vof undesired shading components.
  • the described operation of unit 33 in removing the undesired shading components from the generated signal may be considered from a slightly diifer'ent view.
  • the signal voltages developed by the camera tube under the inuence -of the scanning beam are inversely related to the values of incident light in the ⁇ image focused on the targetl electrode. In other words. small values of signal voltage are obtained during the scanning of those portions of the target electrode that are brilliantly illuminated, while large values' of signal voltage are obtained during the scanning of asados l tentials are supplied from sources indicated as +B and Se.
  • the described amplifier arrangement may be substituted for video-frequencyl amplifier 34 in the television system of Fig. 1 for selecting the modulated carrier wave from the output circuit of the generator. After amplification, this wave is applied to diode 35 where its modulation components are derived and delivered tb combining amplifier 2l for transmission.
  • This modified form of the invention operates by virtue of the fact that a carrier wave modulated by the desired video-frequency signal components is produced ,across loadv impedance when the beam current of generator I5 is periodically interrupted at a carrier-frequency rate during the scanning interval.
  • the carrier frequency of this modulated wave is equal to the frequency of beam current interruption so that the darker portions of .the target. Accordingly,
  • the sig'- nal obtained from the generator should represent an absolute level of picture brightness comparable to the white level. Therefore, the periodic interruption of the beam current .effectively produces recurrent signal components having a predetermined datum level corresponding to the white level of the image to be transmitted.
  • Unit 33 in stabilizing the generated signal establishes the recurrent signal level which represents an absolute level of incident light at a xed potential and thus removes the undesired shading components.
  • the beam current control potential supplied by generator 32 should have a substantially rectangular pulse wave form. It is well known that vsignals of such wave form are rich in harmonics whereby a wide pass band is required to translateA them without distortion. 'I'he pass band requirement maybe reduced considerably -by utilizing a or other suitable system of Fig. 1 operates substantially as described to ldevelop a ⁇ television signal which includes the desired video-frequency components but which is substantially free of undesiredshading components.
  • Fig. 8 there is disclosed a modification of the frequency-responsive means which is coupled to generator Isin accordance with the present invention for deriving a signal that includes comprising a transformer v4 5 double-tuned by condensers Il, included in its output circuit.
  • Each i'llter section is tuned to the carrier frequency of a modulated carrier wave which, as
  • a self-biasing arrangement consisting of a resistor 5t, by-passed.. for high-frequency signals bycondenser 5l, is provided in accordance with conventional practice and suitable operating-porange from 0 to fr and include desired video-fre if the interruption frequency is at least twice as high as the highest video-frequency signal' component generatedfupper and lower sidebands of modulation components individually representing the desired video-frequency signal components are produced and may be readily selected from the output circuit of the generator through a bandpass filter arrangement of the type just described.
  • the undesired shading components do not appear as modulation on the carrier wave since the shading signal has substantially the same value during intervals when the beam is effective and sucneeding intervals when the beam current is interrupted so long as the period of interruption is high compared with the average transit time of the returning secondary electrons.
  • the modulated carrier wave available in the output circuit of the generator as illustrated by curve B of Fig. 9, comprises a carrier-wave component having a carrier frequency fz, a lower sideband of modulation components extending over the'frequency range fa-h, and an upper sideband of modulation components extending over the frequency range .f2-f4. the sidebands of modu. lation individually representing the desired videofrequency components.
  • the modulated carrier wave is spaced in the frequency spectrum from the range O-ji, it may be readily selected to the exclusion of shading components by adjusting the tuned circuits of the radio-frequency amplier to have a mean operating frequency f2 and a pass band corresponding to the frequency range fs-fl. If necessary, damping resistors may be added to the tuned circuits in well-known Y manner to obtain the required frequency range for the lter circuits. These resistors are indicated in dotted construction in Fig. 8 since they may be comprised in part or in whole of the inherent resistances of the tuned circuits.
  • the modulated wave is applied to diode 3'5 where its modulation components which represent the desired Vshading components. then beapplied to diode 'may be transmitted directly Vassesses components derived at theutilizingapparatus, all
  • generator 32 need not necessarily be operated at afixed frej video-frequency components are derived and supplied to combining amplier 2
  • cooperation with the quency-responsive means coupled to tube l having a frequency characteristic related to the frequency at which the beam'current is decreased or interrupted for deriving a signal for transmisthe radio-frequency amplifier of Fig. s in diode 35 comprises fre-l sion which comprises the modulation components l of the modulated-carrier signal developed in the tube and which is substantially freeof undesired shading components.
  • a radio-frequency ampliilerof the type disclosed in Fig. 8 may be coupled to the load impedance of tube
  • the pass-band characteristics ofthe amplier are to be chosen in the manner already described so that the amplifier comprises frequency-responsivemeans coupled to ,the tube having a frequency characteristic related tothe frequency at whichthe beam current is decreased or interrupted for deriving a signal which comprises the modulated carrier wave and which is .substantially free of undesired shading components.
  • the modulated carrier wave, after amplication, may be applied directly to an antenna system 'or it may be. applied to a frequency changer and heterodyned toa frequency more suitable for radiation. In these applications the necessary synchronizing signals may be conveniently transmitted to the utilizing apparatus by way of a separate channel or carrier wave.
  • the radio-frequencyamplifier may be adjusted, if desired, to select only one of the sidebands of modulation. It will'also be understood that the pass band of theamplifier need only be sufficiently wide to select those sideband com ⁇ ponents that represent the video-frequency-signal components which the associated apparatus is capable of utilizing. In other words.
  • the receiving apparatus is able to utilize only a limited portion of the video-frequency -signal components'produced in-the generator 15. Accordingly the phrase "desired'signal components asemployed.
  • generator '3 2 may l be operated at avfrequency comparable to that of the highest video-frequency signal component to 'l be generated. Inf such a case, however, it is necessaryl to adjust the tuned circuits of the radiofrequency amplifier to select theuppersideband #fof modulation components in order to obtain a signal which is substantially free of undesired
  • the selected signal may components are derived and supplied tofcomloining amplier 2l for transmission,
  • the phrase .means for periodically and substantiahy decreasing the ycurrent lof :the beam and similar expressions used'in the foregoingr de. lscription and 'in the appended' vclaims is intended to include both fixed-frequency and variable-frethis generator.
  • a signal-generating system comprising, a
  • a signal-generating ysystem comprising, a
  • a for scanning said target electrode during a scantrode in accordance with a signal to be generated a source of beam current in said tube, means for scanning said target electrode during a scanning interval with said beam to generate desired signal components having frequencies that extend over a range determined by the charge distribu- ⁇ tion on said target electrode and which also develops undesired shading components with saiddesired components, means for periodically and substantially decreasing the current of said beam from a predetermined value during said scanning interval at a frequency which is atleast twice as high as the highest-frequency signal component generated, and frequency-responsive means coupled tosaid tube having a frequency characteristic related to the frequency at which said beam current is decreased for deriving a signalV which includes -said desired signal components and which is substantially free of said undesired shading components.
  • a signal-generating system comprising, a cathode-ray signal-generating tube, a, photosensitive target electrode in said tube, means for establishing a charge distribution on said target electrode in accordance with a signal to be genersource of beam current in said tube, means ning interval with said beam to generate desired signal componentshaving frequencies that extend over a range determined bythe charge distribution on said target electrode and which also develops undesired shading components with said desired components, means for periodically interrupting the current of said beam during said scanning interval at a frequency which is at least as high as the highest-frequency signal component generated, and frequency-responsive means coupled to said tube having a frequency characteristic related to the frequency at which said beam current is interrupted for-deriving a signal -which includes said desired signal components and which is substantially free of said undesired shading components.
  • a television signal-generating system comprising, a cathode-ray signal-generating tube. a photosen'sitive target electrode in said tube, means for establishing a charge distribution on said target electrode in accordance with an image to -be generated, a source of beam current in said tube, means for scanning said target electrode during a scanning interval with said beam to generate detrode during a scanning interval with said beam ,u
  • VA signal-generating system comprising, a
  • cathode-ray signal-generating tube having a control electrode, a photosensitive target electrode in said tube, means for establishing a charge distribution on said target electrode in accordance with a signal to be generated, a source of beam current in said tube, means for scanning said target electrode during a scanning interval with said beam to generate desired signal components having frequencies that extend over a range determined by the charge condition of said target electrode and which also develops undesired shading components with said desired components, means for applying to said control electrode a control potential having a rectangular-pulse wave form for sired video-frequency signal components having frequencies that extend over a range determined by the charge distribution on said target electrode and which also develops undesired shadingA components with said desired-components, means for periodically and lsubstantially decreasing the current of said beam from a predetermined value during said scanning interval at a frequency which is at leasthas high as the highest videofrequency signal component generated, and frequency-responsive means coupled to said tube having a frequency characteristic related to the frequency at which said beam current is decreased for deriving a signal which
  • a signal-generating system comprising, a cathode-ray signal-generating tube having a control electrode, a. photosensitive target electrode in said tube, means for establishing a charge distribution on said target electrode in accordance with a. signal to be generated, a source of beam current in said tube, means for. scanning said target elecperiodically and substantially decreasing the current of said beam from a predetermined value during said scanning interval at a frequency which is at least as high as the highest-frequency signal componentl generated, and frequency-responsive means coupled to said tube having a frequency characteristic related to the frequency at which said beam current is decreased for deriving a signal which includes said desired signal components and which is substantially free of said undesired shading components.
  • a signal-generating system comprising, a cathode-ray signal-generating tube having a control electrode, a photosensitive target electrode in said tube, means for establishing a charge distribution on said target electrode in accordance with a signal to be generated, a source of beam current in said tube, means for scanning said target electrode during a scanning interval with said beam to generate desired signal components having frequencies that extend over a range determined by the charge distribution on said target electrode and which also develops undesired shading components with said desired components, means including a high-frequencyl generator for applying to said control electrode a control potential for periodically and substantially decreasing the current of said beam from a predetermined value during said scanning interval at a frequency which is at least as high as the highest-frequency signal component generated, and frequency-responsive means coupled to said tube having a frequency characteristic related to the frequency. at which said beam current is decreased for deriving a signal which includes said desired signal coinponents and which is substantially free of said undesired shading components.
  • a signal-generating system comprising,4 a cathode-ray signal-generating tube, a photosensitlve target electrodeI in said tube, means for establishing a charge distribution on said target electrode in accordance with a signal to be generdecreased for deriving y ning interval with said beam ated, a source of beam current in said tube, means for scanning said'target electrode during a scani to generate desired signal components having tribution on said target electrode and which also develops undesired shading components with said desired components, means for periodicallyand substantially interrupting the current of said beam during said scanning interval at a frequency which is at least as high as the highest-frequency signal component generated, and peak-rectifying means coupled to said tube having a time-constant which is long with respect to theperiod of' said interruption frequency for deriving a signal which includes said desired signal components and which is substantially free of said undesired Shad-- ing components.
  • a signal-generating system comprising, a
  • cathode-ray signal-generating tube a photosensitive target electrode in saidl tube, means for establishing a charge distribution on said target electrode in accordance with a signal to be generated, a source of beam current in said tube, means substantially interrupting the currentof saidk beam during said scanning interval at a frequency which is at least as high as the highest-frequency signal component generated to produce recurrent signal components having a predetermined datum level, and means coupled to said tube having a frequency characteristic related to the frequency at which said beam 'is interrupted for stabilizing said last-named signal components at a fixed signal level to derive a signal which includes said frequencies that extend over'a range determined by the charge disdesired signal components and which is substanv tially free of said undesired shading components.
  • a television signal-generating system comprising, a cathode-ray signal-generating tube, a photosensitive target electrode in said tube, means for establishing a charge distribution on said target .electrode in accordance with an image tob generated, a source of beam current in said tube, means for scanning said target electrode during a scanning interval with said beam to generate desired video-frequency signal components having frequencies that extend over a range deter- ⁇ mined by the charge distribution on said target electrode and which also develops undesired shadrupting the current of said beam during said l scanning interval at a frequency which is at least as high as the highest video-frequency signal component generated to produce recurrent signal components having a datum level correspondingfrequency signal component y a carrier signal modulated by said desired signal components, and frequency-responsive means t yteristic related v tion components.
  • a source of beam current in said tube means for scanning said target electrode during a scanning interval with said beam Ato generate desired signal components having frequencies that extend over a range dition ofsaid target electrode and which also develops undesired shading components with said desired components, means for periodically and substantially decreasing the current of said beam during said scanning which is at least twice'as high as the highestgenerated to develop coupled to said tube having a frequency charactothe frequency at which said beam current is decreased for deriving a signal which comprises said modulated carrier signal and which is substantially free of said undesired shading components.
  • a signal-generating system comprising, a
  • cathode-ray signal-generating tube afphotosensitive target electrode in said tube, means for establishing a charge electrode in accordance with a signal to be generated, a source of beam current inl said tube, means for scanning.
  • said target electrode during a scanning interval with said beam to generate desired signal components having frequencies that extend over a range charge distribution on said target electrode and which also develops undesired shading compo- ⁇ nents with said desired components, means forA periodically' and substantially decreasing the current of said beam during said scanning interval at a frequency which is highest-frequency signal component generated to develop r.
  • a signal-generating system comprising, a
  • cathode-ray signal-generating tube a photosenf sitive target electrode in said tube, ing components with said desired components
  • a signal-generating system comprising, a nal component generated to develop a carrier cathode-ray signal-generating tube, a photosensignal modulated by said desired signal compositive target electrode in said tube, means for nents, and frequency-responsive means coupled establishing a charge distribution on said target l0 to said tube having a frequency characteristic reeletrode in accordance with a signal to be translated to the frequency at which said beam curmitted, a source of beam current in said tube, rent is decreased for deriving a signal for transmeans for scanning said target electrode during mission which comprises4 modulation components a scanning interval with said beam to generate of said modulated carrier signal corresponding to desired signal components having frequencies )5 said desired components and which is substanthat extend over a range determined by the tially free of said undesired shading components. charge distribution on said target electrode and c ARTHUR V. LOUGHREN.

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US481104A 1943-03-30 1943-03-30 Signal-generating system Expired - Lifetime US2396865A (en)

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GB5846/44A GB579600A (en) 1943-03-30 1944-03-29 Television signal-generating system

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2658104A (en) * 1949-12-30 1953-11-03 Du Mont Allen B Lab Inc Television shading signal and clamping circuit

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB635068A (en) * 1946-09-10 1950-04-05 Cfcmug Improvements in or relating to circuit arrangements for use with television transmitting tubes

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2658104A (en) * 1949-12-30 1953-11-03 Du Mont Allen B Lab Inc Television shading signal and clamping circuit

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