Sampled data automatic gain control circuit

Claim 2

An automatic gain control circuit which comprises, in combination: a variable gain circuit for clamping an applied signal to a selected reference level; controllable means for selectively sampling the amplitude of said clamped signal; means responsive to said clamped signal for generating a signal to control selectively said sampling means; and means responsive to said sampled signal for developing a signal to control the gain of said variable gain clamp circuit.

Claim 3

The circuit as defined in claim 1, wherein said means for generating said sampling control signal includes: means for separating a selected signal portion from said clamped signal; and means responsive to said separated signal for selectively generating a trigger signal.

Claim 4

The circuit as defined in claim 1, wherein said variable gain clamp circuit further generates a signal as an indication that said received signal is clamped.

Claim 5

The circuit as defined in claim 3, wherein: said received signal is a composite video signal having synchronizing pulses; and said clamp indication signal indicates that individual ones of said synchronizing pulses are clamped to said reference level.

Claim 6

The circuit as defined in claim 4, wherein said sampling control signal generating means includes: means for separating said synchronizing pulses from said composite video signal; and means responsive to said separated synchronizing pulses and to said clamp indication signals for generating a sampling control signal only when each of said separated synchronizing pulses is in coincidence with its corresponding clamp indication signal.

Claim 7

The circuit as defined in claim 4, wherein said sampling control signal generating means includes: means for separating said synchronizing pulses, characterized by leading and trailing edges, from the composite video signal; means responsive to the trailing edge of each of said separated synchronizing pulses for developing first trigger signals; means responsive to said clamp indication signals for developing second trigger signals; AND gate means responsive to said first and said second trigger signals for developing third trigger signals; and pulse generator means responsive to said third trigger signals for selectively generating delayed pulse signals, said delay interval being predetermined so that a selected portion of said synchronizing pulse is sampled in amplitude.

Claim 8

An automatic gain control circuit which comprises: a variable gain amplifier having input and output terminals; means for applying a received composite video signal to the input of said amplifier; a clamp circuit having first and second outputs for clamping a gain controlled video signal developed at the output of said amplifier to a selected reference level and for developing a signal which is an indication that said video signal is clamped to said reference level, said clamped video signal being developed at said first output terminal and said clamp indication signal being developed at saId second output terminal; controllable means for selectively sampling the amplitude of a predetermined portion of said clamped video signal; means responsive to said clamped video signal and to said clamp indication signal for generating a signal to control selectively said sampling means, said control signal means being responsive only to a selected coincidence of said clamped video signal and said clamp indication signal; and means responsive to said sampled signal for developing a signal to control the gain of said variable gain amplifier.

Claim 9

An automatic gain control circuit which comprises: a variable gain amplifier having input and output terminals; means for applying a received composite video signal to the input of said amplifier; a clamp circuit having first and second outputs for clamping a gain controlled video signal developed at the output of said amplifier to a selected reference level and for developing a signal which is an indication that said video signal is clamped to said reference level, said clamped video signal being developed at said first output terminal and said clamp indication signal being developed at saId second output terminal; controllable means for selectively sampling the amplitude of a predetermined portion of said clamped video signal; means responsive to said clamped video signal and to said clamp indication signal for generating a signal to control selectively said sampling means, said control signal means being responsive only to a selected coincidence of said clamped video signal and said clamp indication signal; and means responsive to said sampled signal for developing a signal to control the gain of said variable gain amplifier.

Claim 10

The circuit as defined in claim 7, wherein said clamp indication signal denotes that individual ones of synchronizing pulses of the composite video signal are clamped to said reference level: wherein said sampling control signal generating means includes; means for separating said synchronizing pulses from the composite video signal; means selectively responsive to each of said separated synchronizing pulses for generating first trigger signals; means responsive to said clamp indication signal for generating second trigger signals; AND gate means responsive to coincident application of said first trigger signals and their associated second trigger signals for generating third trigger signals; and a pulse generator responsive to said third trigger signals for developing delayed sampling control signals, said delay being set at a predetermined interval so that a selected portion of said synchronizing pulses is sampled in amplitude

Claim 11

A controlled gain transmission circuit which comprises: means for clamping an applied signal having periodic intervals of similar signal characteristics to a prescribed reference level; means for determining that individual portions of said applied signal occurring during said periodic intervals have been clamped to said reference level, said determining means generating a signal representative of the portions of said applied signal which have been clamped; means responsive to the signal generated by said determining means for generating a control signal representative of the amplitude of said applied signal by comparing said applied signal to a predetermined signal level only during said periodic intervals in which said applied signal has been clamped; and means for utilizing said control signal to adjust the amplitude of said applied signal until a new control signal is produced.

Claim 12

A controlled gain transmission circuit which comprises: means for clamping an applied signal having periodic intervals of similar signal characteristics to a prescribed reference level; means for determining that individual portions of said applied signal occurring during said periodic intervals have been clamped to said reference level, said determining means generating a signal representative of the portions of said applied signal which have been clamped; means responsive to the signal generated by said determining means for generating a control signal representative of the amplitude of said applied signal by comparing said applied signal to a predetermined signal level only during said periodic intervals in which said applied signal has been clamped; and means for utilizing said control signal to adjust the amplitude of said applied signal until a new control signal is produced.

Claim 13

The circuit as defined in claim 9 wherein said control signal generating means includes means responsive to said determination signal for inhibiting the comparison of said applied signal with said predetermined signal during intervals in which said applied signal is not clamped.

Claim 14

The circuit as defined in claim 9 wherein said control signal generating means includes means responsive to said determination signal for initiating the comparison of said applied signal to said predetermined signal.