US2299945A - Direct current reinserting circuit - Google Patents

Direct current reinserting circuit Download PDF

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Publication number
US2299945A
US2299945A US367323A US36732340A US2299945A US 2299945 A US2299945 A US 2299945A US 367323 A US367323 A US 367323A US 36732340 A US36732340 A US 36732340A US 2299945 A US2299945 A US 2299945A
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US
United States
Prior art keywords
circuit
pulses
keying
resistor
diodes
Prior art date
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
Application number
US367323A
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English (en)
Inventor
Karl R Wendt
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RCA Corp
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RCA Corp
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Filing date
Publication date
Priority to BE475115D priority Critical patent/BE475115A/xx
Priority to NL73155D priority patent/NL73155C/xx
Application filed by RCA Corp filed Critical RCA Corp
Priority to US367323A priority patent/US2299945A/en
Application granted granted Critical
Publication of US2299945A publication Critical patent/US2299945A/en
Priority to FR989230D priority patent/FR989230A/fr
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
    • H04N5/18—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level by means of "clamp" circuit operated by switching circuit
    • H04N5/185—Circuitry for reinsertion of DC and slowly varying components of signal; Circuitry for preservation of black or white level by means of "clamp" circuit operated by switching circuit for the black level

Definitions

  • a further object of my invention is to provide an improved D. C. reinserting circuit which is both simple in design and effective in operation.
  • a further object of the invention is to provide an improved and simplified si nal correction circult of the type in which a condenser in the circuit is keyed for both charge and discharge.
  • a still further object of the invention is to provide an improved signal correction circuit of the keyed type in which the keying pulses are balanced out and prevented from mixing with the sisna
  • a still further object of the invention is to provide an improved signal correction circuit .in which any sawtooth waves that may be produced in the keying circuit are balanced out.
  • Still another object of the invention is to provide an improved method of and means for obtaining a level setting voltage in keyed signal correction circuits.
  • the charge of a condenser in the grid circuit of a vacuum tube is controlled by means of two diodes which are keyed by periodically recurring pulses, such as synchronizing pulses.
  • a synchronizing or keying pulse Upon the occurrence of a synchronizing or keying pulse, one of the diodes is rendered conducting and the condenser will discharge therethrough a certain amount if its charge should be reduced to provide the correct D. C. reinsertion', or it will charge a certain amount through the other diode if its charge should be increased.
  • bothdiodes are held nonconducting by means of a biasing voltage. Since both diodes are biased in this way, the reinserting circuit may be operated with an applied signal of either polarity.
  • the diodes are provided with a level setting voltage which is produced automatically by the keying circuit.
  • FIG. 2 is a circuit diagram of another embodiment of my invention.
  • Figure 3 is a group of curves which are referred to in explaining the operation of the circuits of Figures 1 and 2, and
  • Figure 4 is a group of curves which are referred to in explaining the operation of the circuits of Figures 1 and 3 for the case where the polarity of the signal is reversed as compared with the polarity indicated in Figure 1.
  • the invention is shown applied to a television system in which there is produced a composite signal consisting of picture signals, periodically recurring line synchronizin pulses and periodically recurring framing pulses.
  • a composite signal consisting of picture signals, periodically recurring line synchronizin pulses and periodically recurring framing pulses.
  • the peaks of the synchronizing pulses have been made to go to a fixed voltage level such as a fixed number of volts beyond black in the picture before the direct current and low frequency have been suppressed.
  • This may be accomplished in various ways, as by varying the clipping level 01' a vacuum tube in the way described in .Patent No. 2,192,121, issued February 27, 1940, in the name of Alda V. Bedford, or by utilizing a suitable mask with a scansistor R2.
  • Pulses positive polarity are supity that it appears in the output circuit with the synchronizing pulses of positive polarity as indicated at H.
  • the pulses ii are line synchronizing pulses set on a black" or blacker than black level or pedestal indicated at i2.
  • Picture signal is shown at l3.
  • the tube It supply an output signal in which the peaks of all the synchronizing pulses go to a fixed voltage level. If this is done, correction is made for signal components that have been lost (1, e.,
  • the amplifier tubes i0 and i6 which may be conventional tetrodes or pentodes, are coupled by a coupling condenser C which, as will be explained hereinafter, has a suitable capacity value to permit, first, the necessary initial charging and, later, the necessary additional charging or discharging in cooperation with the complete circuit for the desired correction or reinsertion of lost components.
  • the reinserting circuit comprising a pair of diodes 2
  • and the plate of diode 22 are connected together and both connected through a conductor 26 to the control grid of amplifier tube Hi.
  • and 22 are connected together through a reor to discharge through the diode 2
  • the keying pulses may be supplied over a conductor 36, through clipping tubes indicated at 35, through switches 31 and 38, and through a coupling condenser 39 to the grid of tube 3
  • may be properly biased by means of a biasing battery 4
  • is provided with both a plate resistor RI and a cathode replied from resistor R
  • the resistors RI and R2 are of equal resistance so that the keying circuit is balanced to prevent the keying Pulses from appearing on the grid of the tube l6;
  • the clipping means 35 may consist of two resistance coupled amplifier tubes, at least one of which is so biased as to pass only the synchronizing pulses H, as is well understood in the art.
  • and 22 are so connected that they are made conducting by a negative pulse on the grid of tube 3
  • is sumcient to drive the tube 3
  • the conductor 26 (and, therefore, the grid of tube I6) is driven to the potential of the alternating current midpoint of the resistor 21.
  • this A. C. midpoint is at the middle of resistor 21; It follows that the grid of tube i5 is driven to a potential with respect to ground which is determined by the potential of the said A. C. midpoint with respect to ground. This potential is the previously mentioned level setting voltage.
  • the preferred method of obtaining the level setting voltage is the one employed in the circuit oi Figure 1 where a resistor 46 is connected between ground and a point on the resistor 21 through a variable tap 41.
  • the level setting voltage is then the voltage between the A. C. midpoint and the tap 41 as indicated by the legend, Level setting, this voltage resulting from current fiow through the resistor 21 which is produced as follows:
  • Each keying pulse causes current to flow through the coupling condensers 28 and 29 and the diodes 2
  • the condensers 28 and 29 receive a charge.
  • the condensers 28 and 29 discharge a certain amount through a path including the resistor 21, whereby, between keying pulses, there is always direct current fiowing through resistor 21. This discharge path may be traced from the condenser 29, through the resistor 21, the condenser. 2
  • the condenser C acquires a slight additional charge through diode 22 ii the synchronizing pulses II have increased in amplitude with respect to the A. C. axis of the signal, and that condenser C discharges a small amount through diode 2
  • the circuits of Figure 1 and 2 are the same I except that in Figure 2 the level setting voltage is obtained from a biasing source such as a battery 5
  • Such a sawtooth wave may be produced by the action of the comparatively long duration framing pulses, which, like the line pulses, cause the condensers 28 and 29 to charge suddenly, after which they discharge slowly through th resistor 21.
  • Any saw-tooth voltage that may be produced by the line pulses II is usually of such small amplitude as to be negligible even if not balanced out.
  • the keying pulses may be supplied from points other than the output circuit of amplifier It.
  • the'switch 38 may be connected to a conductor 52 leading from the input circuit of the amplifier l0. With this connection, however, it may be desirable to provid additional ampliil cation just preceding the tube 3 I.
  • the keying pulses may be supplied over a conductor 53 from a separate source, such as the synchronizing pulse generator of the television transmitter, by connecting the switch 31 to the conductor 53.
  • the reinserting circuit keyed only during the occurrence of the pedestal l2. This may be accomplished by properly delaying the keying pulses, as by means of a delay circuit 55 which is shown included in the circuit leading from the above-mentioned pulse generator (not shown).
  • circuits of Figures 1 and 2 may be employed regardless of the polarity of the signal applied to the grid of tube i 6. If the synchronizpoint, the clipper circuit 35 should be designed so that negative keying pulses still are-supplied to the grid of tube 3
  • the level setting voltage must now be increased in value. Whereas a small level setting voltage, such as one volt for example, was satisfactory before (see Figure 3), it is now necessary to have a level setting voltage suflicient to prevent picture signal peaks from driving the grid of tube l6 positive. In other words. the level setting voltag should now be greater than the signal voltage measured from the level setting point (which is peak of pulse H in Figure 4) to the peak of the picture signal I 3.
  • the bias on the grid of tube It is the D. C. voltage across condenser C minus the plate voltage on the tube I0.
  • the keying pulses of opposite polarity may be applied to the diodes 2
  • the circuit should be balanced if the full capabilities of the correction circuit ar to be utilized.
  • a circuit for correction of a signal supplied from a certain source and having recurring control periods the combination of an amplifier tube having a control grid and a cathode, a condenser connected in series with said source and said control grid, and a charging and discharging circuit for said condenser which comprise a pair of diodes so connected that said condenser may charge through one of them and discharge through the other one when the diodes are conducting, and keying means for making said diodes conducting during portions of said control periods and nonconducting between said control periods, said keying means comprising a circuit for applying keying pulses of opposite polarity to said diodes.
  • said last means comprises a balanced circuit whereby said keying pulses do not appear on said control grid.
  • suping pulses II are of negative polarity at thisplied from a certain source and having recurring control periods, an element to which it is desired to apply a corrected signal, a condenser connected in series with said source and said element, a pair of diodes each having a cathode and a plate, a direct current connection from the cathode of one diode and the plate of the other diode to said element, a resistor connected between the other cathode and other plate of said diodes, means for providing keying pulses during said control periods, and means for applying said keying pulses to one end of said resistor with a certain polarity and for applying said keying pulses to the other end of said resistor with the opposite polarity.
  • an amplifier tube having a control grid and a cathode, a coupling condenser connected to said control grid, means for feeding said composite signal through said coupling condenser to said control grid, and a charging and discharging circuit for said condenser which comprisesia pair of diodes so connected that said condenser may charge through one of said diodes and discharge through the other of said diodes when said diodes are made conducting, means for so biasing said diodes that said condenser can not discharge therethrough during certain signal intervals, means for producing keying pulses of opposite polarity, and means for applying between said intervals keying pulses of one polarity to one of said diodes to render it conducting and for simultaneously applying keying pulses of the opposite polarity to the other of said diodes to render it conducting.
  • an element to which it is desired to apply a corrected signal in series with said source and said element, a condenser connected in series with said source and said element, a pair of diodes each having a cathode and a plate, a direct current connection from the cathode of one diode and the plate of .the other diode to said element, a resistor connected between the other cathode and other plate of said diodes, means for providing keying pulses during said control periods, keying circuit condensers, and means for applying said keying pulses through one of said keying circuit condensers to one end of said resistor with a certain polarity and for applying said keying pulses through the other of said keying circuit condensers to the other end of said resistor with the opposite polarity.
  • a circuit for correction of a composite signal supplied from a certain source and consisting ofsignals and recurring control pulses the combination of an amplifier tube having a control grid and a cathode, a condenser connected in series with said source and said control grid, and a charging and discharging circuit for said condenser which comprises a pair of diodes so connected that said condenser may'charge through one of them and discharge through the other one when the diodes are conducting, and keying means for making said diodes conduct ing between said signal intervals and-nonconducting during said intervals, said keying means comprising a balanced circuit for applying keying pulses of opposite polarity to said diodes.
  • a circuit for correction of a composite signal consisting of signals and recurring control pulses the combination of an amplifier tube having a control grid and a cathode, a coupling condenser connected to said control grid, means for feeding said composite signal through said coupling condenser to said control grid, and a charging and discharging circuit for said condenser which comprises a pair of diodes each having a plate and a cathode, the plate of one diode and the cathode of the other diode being connected to said control grid, the other plate and cathode of said diodes being connected to each other through a resistor, means for holding a point on said resistor at a certain potential with respect to ground, said potential being of such polarity that the diodes are nonconducting during the signal intervals, and means for applying keying pulses of opposite polarity to the ends of said resistor for making said diodes conducting between said signal intervals.
  • a circuit for correction of a composite signal consisting of signals and recurring control pulses, said pulses having an amplitude at least as great as said signals of like polarity the combination of an amplifier tube having a control grid and a cathode, a coupling condenser connected to said control grid, means for feeding said composite signal through" said coupling condenser to said control grid, and a charging and discharging circuit for said condenser which comprises a pair of diodes each having a plate and a cathode, the plate of one diode and the cathode of the other diode being connected to said control grid, the other plate and cathode of said diodes being connected to each other through a resistor having an alternating current midpoint, a second resistor connected between ground and a point on said first resistor which point is removed from said midpoint whereby said midpoint is held at a certain potential with respect to ground, said potential being of such polarity that the diodes are nonconducting during the signal interval

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US367323A 1940-11-27 1940-11-27 Direct current reinserting circuit Expired - Lifetime US2299945A (en)

Priority Applications (4)

Application Number Priority Date Filing Date Title
BE475115D BE475115A (enrdf_load_stackoverflow) 1940-11-27
NL73155D NL73155C (enrdf_load_stackoverflow) 1940-11-27
US367323A US2299945A (en) 1940-11-27 1940-11-27 Direct current reinserting circuit
FR989230D FR989230A (fr) 1940-11-27 1947-07-30 Circuit-correcteur

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US367323A US2299945A (en) 1940-11-27 1940-11-27 Direct current reinserting circuit

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US2299945A true US2299945A (en) 1942-10-27

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US367323A Expired - Lifetime US2299945A (en) 1940-11-27 1940-11-27 Direct current reinserting circuit

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US (1) US2299945A (enrdf_load_stackoverflow)
BE (1) BE475115A (enrdf_load_stackoverflow)
FR (1) FR989230A (enrdf_load_stackoverflow)
NL (1) NL73155C (enrdf_load_stackoverflow)

Cited By (33)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2443434A (en) * 1944-05-23 1948-06-15 Press Wireless Inc Automatic signal bias control means and apparatus
US2457268A (en) * 1946-06-08 1948-12-28 Rca Corp Signaling
US2525106A (en) * 1946-11-21 1950-10-10 Rca Corp Electronic keyer for direct current restoration
US2547648A (en) * 1946-01-25 1951-04-03 Hazeltine Corp Automatic contrast control system for television apparatus
US2547020A (en) * 1944-12-26 1951-04-03 Int Standard Electric Corp Method and means for the transmission of low-frequency calls intelecommunication systems by interrupting the carrier
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2554317A (en) * 1946-12-18 1951-05-22 Rca Corp Clamp circuit
US2559719A (en) * 1948-09-25 1951-07-10 Rca Corp Frequency-stabilizing method and system
US2564017A (en) * 1949-06-04 1951-08-14 Bell Telephone Labor Inc Clamp circuit
US2591088A (en) * 1945-11-30 1952-04-01 Us Navy Video blanking circuit
US2636080A (en) * 1949-01-26 1953-04-21 Bell Telephone Labor Inc Balanced diode clamper circuit for low-frequency restoration
US2647161A (en) * 1947-09-17 1953-07-28 Motorola Inc Double triode clamping circuit for direct current reinsertion
US2675424A (en) * 1950-07-11 1954-04-13 Pye Ltd Low-frequency interference suppressor
US2692333A (en) * 1951-08-02 1954-10-19 Rca Corp Wave shaping circuit
US2710310A (en) * 1948-11-20 1955-06-07 Sylvania Electric Prod Variable level synchronizing signal clipper
US2760008A (en) * 1950-08-30 1956-08-21 Rca Corp Amplifier having controllable signal expansion and compression characteristics
US2792496A (en) * 1953-09-24 1957-05-14 Rca Corp Stabilized direct current setting apparatus
US2802102A (en) * 1951-06-08 1957-08-06 Gen Electric Co Ltd Electrical pulse slicing circuit
US2802101A (en) * 1951-06-23 1957-08-06 Raytheon Mfg Co Pulse stretchers
US2833862A (en) * 1953-09-11 1958-05-06 William A Tolson Multiplexing commutators
US2836719A (en) * 1955-08-23 1958-05-27 California Research Corp Methods and apparatus for shifting seismic record timing pulses
US2843737A (en) * 1954-09-20 1958-07-15 Rca Corp Sweep expander bias circuit
US2861185A (en) * 1956-01-27 1958-11-18 Bell Telephone Labor Inc Compensated plate type limiter
US2894131A (en) * 1955-07-18 1959-07-07 Hoffman Electronics Corp Electronic selective circuit or the like
US2898457A (en) * 1954-11-30 1959-08-04 Underwood Corp Amplifier circuit
US2929015A (en) * 1955-10-26 1960-03-15 Fleming Lawrence Electrically variable impedance
US2947864A (en) * 1955-12-05 1960-08-02 Minnesota Mining & Mfg Apparatus for recording television signals
US2975371A (en) * 1958-11-24 1961-03-14 Ibm Clipping level control circuit
US2976356A (en) * 1955-09-09 1961-03-21 Thompson Ramo Wooldridge Inc Slow sweep television system
US2979567A (en) * 1956-09-27 1961-04-11 North Ameircan Philips Company Frequency-shift telegraphy receiver
US3003028A (en) * 1956-12-15 1961-10-03 Philips Corp Circuit arrangement for re-introducing the direct current component of a video signal
US3121224A (en) * 1958-09-08 1964-02-11 Bendix Corp Clutter residue reduction for mti radar systems
US3432763A (en) * 1966-12-13 1969-03-11 Hewlett Packard Co Amplifier employing nonlinear dc negative feedback to stabilize its dc operating point

Cited By (33)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2443434A (en) * 1944-05-23 1948-06-15 Press Wireless Inc Automatic signal bias control means and apparatus
US2547020A (en) * 1944-12-26 1951-04-03 Int Standard Electric Corp Method and means for the transmission of low-frequency calls intelecommunication systems by interrupting the carrier
US2591088A (en) * 1945-11-30 1952-04-01 Us Navy Video blanking circuit
US2547648A (en) * 1946-01-25 1951-04-03 Hazeltine Corp Automatic contrast control system for television apparatus
US2457268A (en) * 1946-06-08 1948-12-28 Rca Corp Signaling
US2525106A (en) * 1946-11-21 1950-10-10 Rca Corp Electronic keyer for direct current restoration
US2550178A (en) * 1946-11-21 1951-04-24 Rca Corp Direct current reinsertion circuit for television systems
US2554317A (en) * 1946-12-18 1951-05-22 Rca Corp Clamp circuit
US2647161A (en) * 1947-09-17 1953-07-28 Motorola Inc Double triode clamping circuit for direct current reinsertion
US2559719A (en) * 1948-09-25 1951-07-10 Rca Corp Frequency-stabilizing method and system
US2710310A (en) * 1948-11-20 1955-06-07 Sylvania Electric Prod Variable level synchronizing signal clipper
US2636080A (en) * 1949-01-26 1953-04-21 Bell Telephone Labor Inc Balanced diode clamper circuit for low-frequency restoration
US2564017A (en) * 1949-06-04 1951-08-14 Bell Telephone Labor Inc Clamp circuit
US2675424A (en) * 1950-07-11 1954-04-13 Pye Ltd Low-frequency interference suppressor
US2760008A (en) * 1950-08-30 1956-08-21 Rca Corp Amplifier having controllable signal expansion and compression characteristics
US2802102A (en) * 1951-06-08 1957-08-06 Gen Electric Co Ltd Electrical pulse slicing circuit
US2802101A (en) * 1951-06-23 1957-08-06 Raytheon Mfg Co Pulse stretchers
US2692333A (en) * 1951-08-02 1954-10-19 Rca Corp Wave shaping circuit
US2833862A (en) * 1953-09-11 1958-05-06 William A Tolson Multiplexing commutators
US2792496A (en) * 1953-09-24 1957-05-14 Rca Corp Stabilized direct current setting apparatus
US2843737A (en) * 1954-09-20 1958-07-15 Rca Corp Sweep expander bias circuit
US2898457A (en) * 1954-11-30 1959-08-04 Underwood Corp Amplifier circuit
US2894131A (en) * 1955-07-18 1959-07-07 Hoffman Electronics Corp Electronic selective circuit or the like
US2836719A (en) * 1955-08-23 1958-05-27 California Research Corp Methods and apparatus for shifting seismic record timing pulses
US2976356A (en) * 1955-09-09 1961-03-21 Thompson Ramo Wooldridge Inc Slow sweep television system
US2929015A (en) * 1955-10-26 1960-03-15 Fleming Lawrence Electrically variable impedance
US2947864A (en) * 1955-12-05 1960-08-02 Minnesota Mining & Mfg Apparatus for recording television signals
US2861185A (en) * 1956-01-27 1958-11-18 Bell Telephone Labor Inc Compensated plate type limiter
US2979567A (en) * 1956-09-27 1961-04-11 North Ameircan Philips Company Frequency-shift telegraphy receiver
US3003028A (en) * 1956-12-15 1961-10-03 Philips Corp Circuit arrangement for re-introducing the direct current component of a video signal
US3121224A (en) * 1958-09-08 1964-02-11 Bendix Corp Clutter residue reduction for mti radar systems
US2975371A (en) * 1958-11-24 1961-03-14 Ibm Clipping level control circuit
US3432763A (en) * 1966-12-13 1969-03-11 Hewlett Packard Co Amplifier employing nonlinear dc negative feedback to stabilize its dc operating point

Also Published As

Publication number Publication date
FR989230A (fr) 1951-09-06
NL73155C (enrdf_load_stackoverflow)
BE475115A (enrdf_load_stackoverflow)

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