Vhf and uhf automatic gain control circuitry derived from a single control voltage

Claim 2

In a television receiver of the type employing a VHF tuner for responding to transmitted television signals in the very high frequency band, and a UHF tuner for responding to transmitted television signals in the ultra-high frequency band, said VHF and UHF tuners each having a separate gain controllable radio frequency amplifier for respectively amplifying said VHF and UHF signals prior to conversion of said signals to video intermediate frequency signals, said receiver further including an automatic gain control circuit having an input responsive to the magnitude of a detected video signal to provide at an output a control signal indicative of the difference of said detected signal from a predetermined value, said control signal being conventionally applied to said radio frequency amplifier in said VHF tuner to control the gain thereof, the improvement therewith of apparatus for developing a second control signal to control the gain of said radio frequency amplifier in said UHF tuner, comprising, a. a first amplifier circuit having a high impedance input terminal and an output terminal, said input impedance of said amplifier being partly a function of the current conducted by said amplifier, b. means coupled to said input terminal of said firsT amplifier circuit responsive to said control voltage, for providing at said output terminal of said amplifier a second control voltage, c. means coupled to said output terminal of said amplifier and responsive to said second control voltage to limit said second voltage at a value determined according to the conduction of said amplifier to prevent said input impedance from substantially varying, and d. means coupled between said output of said first amplifier and said UHF radio frequency amplifier for applying said second control voltage thereto to vary said gain according to the magnitude of said second control voltage.

Claim 3

The apparatus according to claim 1 wherein said first amplifier comprises, a. first and second transistors each having a base, collector and emitter electrode, the collector electrode of said first and second transistors being connected together, the emitter electrode of said first coupled to the base electrode of said second transistor, b. a resistor, coupling the emitter electrode of said second transistor to a point of reference potential, c. means coupled to said collector electrode connection adapted for application thereto of a source of operating potential.

Claim 4

The apparatus according to claim 1 wherein said means coupled to said output terminal of said amplifier, comprises, a. a unilateral current conducting device, having first and second terminals and poled for easy current conduction from said first to said second terminals, said second terminal coupled to the output of said amplifier, b. a voltage divider, c. means coupling said first electrode of said current device to said divider to cause said device to conduct when a voltage at the output of said amplifier is less than the voltage on said first terminal of said current device.

Claim 5

In a television receiver having automatic gain control circuitry for providing an automatic gain control voltage adapted to control the gain of a VHF radio frequency amplifier having a maximum gain for a given positive voltage and a minimum gain for a predetermined negative voltage, said automatic gain control circuitry operating in response to a detected video signal to provide said control voltage between said predetermined negative level and said given positive level to accordingly control the gain of said VHF radio frequency amplifier, the improvement therewith of apparatus for deriving a UHF automatic gain control voltage, comprising: a. a first common base transistor amplifier configuration having an emitter input terminal and a collector output terminal, said amplifier having a gain characteristic which decreases according to an increase in current flow between the emitter to collector path, b. means coupled to said input terminal adapted to receive UHF television signals, c. a second common emitter transistor amplifier configuration having a large input impedance at the base electrode thereof determined in part by the current flowing through said transistor, said transistor having a collector electrode output terminal, d. means coupled to said base electrode of said second amplifier for applying said automatic gain control voltage thereto, to cause said amplifier to provide at said collector electrode a large positive voltage for said predetermined negative voltage and a smaller positive voltage for said given positive voltage, e. means coupled to said collector electrode of said second amplifier and responsive to said smaller positive voltage for limiting said voltage at a desired level, to prevent said input impedance of said second amplifier from decreasing, f. means coupling said collector electrode of said second common emitter transistor amplifier to the base electrode of said first common base amplifier for controlling the gain thereof and therefore the magnitude of said UHF signals.

Claim 6

In a television receiver having automatic gain control circuitry for providing an automatic gain control voltage adapted to control the gain of a VHF radio frequency amplifier having a maximum gain for a given positive voltage and a minimum gain for a predetermined negative voltage, said automatic gain control circuitry operating in response to a detected video signal to provide said control voltage between said predetermined negative level and said given positive level to accordingly control the gain of said VHF radio frequency amplifier, the improvement therewith of apparatus for deriving a UHF automatic gain control voltage, comprising: a. a first common base transistor amplifier configuration having an emitter input terminal and a collector output terminal, said amplifier having a gain characteristic which decreases according to an increase in current flow between the emitter to collector path, b. means coupled to said input terminal adapted to receive UHF television signals, c. a second common emitter transistor amplifier configuration having a large input impedance at the base electrode thereof determined in part by the current flowing through said transistor, said transistor having a collector electrode output terminal, d. means coupled to said base electrode of said second amplifier for applying said automatic gain control voltage thereto, to cause said amplifier to provide at said collector electrode a large positive voltage for said predetermined negative voltage and a smaller positive voltage for said given positive voltage, e. means coupled to said collector electrode of said second amplifier and responsive to said smaller positive voltage for limiting said voltage at a desired level, to prevent said input impedance of said second amplifier from decreasing, f. means coupling said collector electrode of said second common emitter transistor amplifier to the base electrode of said first common base amplifier for controlling the gain thereof and therefore the magnitude of said UHF signals.

Claim 7

The apparatus according to claim 4 wherein said means coupling said collector electrode of said second commoN emitter amplifier to the base electrode of said first common base amplifier, comprises, a. first and second series resistors coupled between the collector electrode of said second common emitter transistor amplifier and a point of reference potential, the junction between said first and second resistors being coupled to the base electrode of said first common base amplifier.

Claim 8

The apparatus according to claim 4 wherein said means coupled to said collector electrode of said second amplifier, comprises, a. a clamping diode having first and second terminals and poled for easy current conduction from said first to second terminal, said first terminal being connected to said collector electrode of said second amplifier, and b. a source of bias voltage coupled to said second terminal.