Television receiver agc system keyed in response to time coincidence of sync and flyback pulses

Claim 2

A keyed automatic gain control system for a television receiver comprising: means for deriving, from a received television signal, a composite video signal having video components during spacedapart horizontal trace intervals and horizontal sync components during intervening horizontal retrace intervals; a horizontal sweep system controlled by said sync components and developing periodically recurring flyback pulses in time coincidence with said sync components when the operation of said sweep system is properly synchronized to said components; coincidence means for producing a keying pulse each time a flyback pulse occurs concurrently with a sync component; an AGC voltage Generator, keyed by the keying pulses, for developing an automatic gain control voltage having a magnitude determined by the peak amplitudes of those sync components that occur in the presence of flyback pulses; and means responsive to said automatic gain control voltage for regulating the gain of said receiver inversely with signal strength variations of the received television signal.

Claim 3

A keyed automatic gain control system according to claim 1 in which said AGC voltage generator includes a sampler for sampling said composite video signal in response to and during the occurrence of each keying pulse, and in which each sample is held until the next succeeding sample is taken.

Claim 4

A keyed automatic gain control system according to claim 1 wherein said AGC voltage generator includes a comparator which, in response to each keying pulse, compares the peak amplitude of the simultaneously occurring sync component with an AGC reference voltage to effectively determine whether said composite video signal has a desired peak amplitude, said AGC voltage generator utilizing such comparisons to control the magnitude of said automatic gain control voltage in order to establish and maintain said composite video signal at said desired peak amplitude and to establish and maintain the peak amplitude of said sync components at a predetermined AGC reference level.

Claim 5

A keyed automatic gain control system according to claim 1 in which said automatic gain control voltage is developed by a capacitor whose charge condition may be changed, thereby to vary the magnitude of said control voltage, only during the occurrence of a keying pulse.

Claim 6

A keyed automatic gain control system according to claim 1 in which said AGC voltage generator includes a capacitor for developing said automatic gain control voltage; and charging-discharging means, normally inoperative but keyed into operation by said keying pulses, for controlling the charge on said capacitor; and in which the charge condition of said capacitor is adjustable only when said charging-discharging means is made operable.

Claim 7

A keyed automatic gain control system according to claim 1 in which said AGC voltage generator includes a capacitor for developing said automatic gain control voltage, a charging circuit for charging said capacitor, and a discharging circuit for discharging said capacitor, and in which a controlled amount of current is translated through at least one of said circuits during the occurrence of a keying pulse when it is necessary to adjust the charge condition of said capacitor to reflect a change in the signal strength of the received television signal.

Claim 8

A keyed automatic gain control system according to claim 1 in which said AGC voltage generator includes a normally inoperative comparator for comparing the instantaneous amplitude of said composite video signal with an AGC reference voltage to effectively measure the peak amplitude of said composite video signal, a capacitor for developing said automatic gain control voltage, and normally inoperative charge-discharge circuitry to be controlled by said comparator to adjust the charge condition of said capacitor in accordance with variations of the amplitude of said composite video signal from a desired peak amplitude, and in which said comparator and said charge-discharge circuitry are rendered operative in response to each keying pulse.

Claim 9

A keyed automatic gain control system according to claim 7 wherein normally cut off gates, included in said comparator and in said charge-discharge circuitry, are rendered conductive by each keying pulse.

Claim 10

A keyed automatic gain control system according to claim 1 and including immunizing means for rendering said system immune to undesired noise components that may be included in said composite video signal.

Claim 11

A keyed automatic gain control system according to claim 1 and including means, effectively responsive to a sudden and substantial change in received signal strength, for developinG for application to said AGC voltage generator keying pulses that are independent of, and not necessarily in time coincidence with, said sync components.

Claim 12

A keyed automatic gain control system according to claim 1 in which said sync components are normally separated from said composite video signal and applied to both said horizontal sweep system and to said coincidence means, and wherein said sweep system is free-running and develops flyback pulses even in the absence of applied sync components; and including means, responsive to the absence of sync components applied to said coincidence means, for keying said AGC voltage generator with the flyback pulses alone.

Claim 13

A keyed automatic gain control system according to claim 1 wherein a clamp capacitor, which charges in response to said sync components, develops and maintains a bias voltage on said coincidence means in order that the keying pulses are normally produced only when the flyback pulses sync in time coincidence with the sync components; said capacitor discharging to remove said bias voltage in response to the absence of a minimum number of successive sync components; and said coincidence means, in the absence of said bias voltage and in response to the flyback pulses, producing output pulses for keying said AGC voltage generator.

Claim 14

A keyed gain control system according to claim 1 in which both said coincidence means and said AGC voltage generator are inductorless and lend themselves readily to circuit integration.

Claim 15

A keyed automatic gain control system for a television receiver comprising: means for deriving a composite video signal having video and horizontal sync components; a separator for separating said sync components from said composite video signal; a free-running horizontal sweep system normally controlled by the sync components from said separator and developing periodically recurring flyback pulses; a keyed AGC voltage generator for developing an automatic gain control voltage having a magnitude determined by the instantaneous amplitude of said composite video signal at the keying times of said generator; means for keying said AGC voltage generator in response to the time coincidence of the flyback pulses and the sync components, during normal operation when sync components are present at the output of said separator, and in response to the flyback pulses alone during transient conditions when there is a rapid and considerable change in received signal strength resulting in an absence of sync components at the output of said separator; and means responsive to said automatic gain control voltage for regulating the gain of said receiver.

Claim 16

A keyed automatic gain control system for a television receiver comprising: means for deriving a composite video signal having video and horizontal sync components; a separator for separating said sync components from said composite video signal; a free-running horizontal sweep system normally controlled by the sync components from said separator and developing periodically recurring flyback pulses; a keyed AGC voltage generator for developing an automatic gain control voltage having a magnitude determined by the instantaneous amplitude of said composite video signal at the keying times of said generator; means for keying said AGC voltage generator in response to the time coincidence of the flyback pulses and the sync components, during normal operation when sync components are present at the output of said separator, and in response to the flyback pulses alone during transient conditions when there is a rapid and considerable change in received signal strength resulting in an absence of sync components at the output of said separator; and means responsive to said automatic gain control voltage for regulating the gain of said receiver.

Claim 17

A keyed automatic gain control system for a television receiver comprising: means for deriving, from a received television signal, a composite video signal having video and horizontal sync components; a free-running horizontal sweep system the operation of which is to be synchronized to said sync components; a keyed AGC voltage generator for developing an automatic gain control voltage having a magnitude determined by the instantaneous amplitude of said composite video signal at the keying times of said generator; means, effectively operative when the peak amplitude of said composite video signal lies within a predetermined amplitude range, for keying said AGC voltage generator only during the occurrences of said sync components even though said sweep system may from time to time be out of synchronization with said sync components; and means responsive to said automatic gain control voltage for regulating the gain of said receiver inversely with signal strength variations of the received television signal.

Claim 18

A keyed automatic gain control system for a television receiver comprising: means for deriving, from a received television signal, a composite video signal having video and horizontal sync components; a free-running horizontal sweep system the operation of which is to be synchronized to said sync components; a keyed AGC voltage generator for developing an automatic gain control voltage having a magnitude determined by the instantaneous amplitude of said composite video signal at the keying times of said generator; means, effectively operative when the peak amplitude of said composite video signal lies within a predetermined amplitude range, for keying said AGC voltage generator only during the occurrences of said sync components even though said sweep system may from time to time be out of synchronization with said sync components; and means responsive to said automatic gain control voltage for regulating the gain of said receiver inversely with signal strength variations of the received television signal.