Gamma control circuit

Claim 2

A gamma control circuit including in combination: a driver amplifier, the gain of which is to be controlled and which includes an amplifier transistor having collector, base, and emitter electrodes; first and second voltage supply terminals for connection across a DC supply voltage; first impedance means coupled in circuit between one of said voltage supply terminals and one of the collector and emitter electrodes of said amplifier transistor, the other of the collector and emitter electrodes of said amplifier transistor being coupled in circuit with said other voltage supply terminal; means for applying input signals to the base of said amplifier transistor; second impedance means; a switching transistor having base, emitter, and collector electrodes; means for connecting said second impedance means and the emitter and collector of said switching transistor in series across said first impedance means in the order named with the collector of said switching transistor being coupled with said one of said voltage supply terminals; voltage divider means connected between said first and second voltage supply terminals, with the magnitude of impedance of said voltage divider means being substantially greater than the magnitude of impedance of said second impedance means; means coupling the base of said switching transistor with said voltage divider means for establishing a predetermined reference potential on the base of said switching transistor, said switching transistor being rendered conductive with the potential on the emitter thereof attaining a value sufficient to forward bias said switching transistor into conduction.

Claim 3

The combination according to claim 1 further including third impedance means connected at a first junction to said first impedance means and wherein the collector electrode of said amplifier transistor is connected to said first voltage supply terminal, with the emitter electrode of said amplifier transistor, said third impedance means and said first impedance means being connected in series in the order named to said second voltage supply terminal, and said second impedance means and the emitter and collector of said switching transistor are connected in series in the order named between said first junction and said second voltage supply terminals.

Claim 4

A gamma control circuit including in combination: first and second voltage Supply terminals for connection across a source of DC supply potential; driver amplifier means, the gain of which is to be controlled, including an amplifier transistor having base, collector and emitter electrodes, the collector of which is connected in circuit with said first voltage supply terminal; means for applying input signals to the base of said amplifier transistor; first impedance means connected in circuit between a first junction coupled with the emitter of said amplifier transistor and said second voltage supply terminal; a plurality of second impedance means; a plurality of switching transistors, each having base, emitter and collector electrodes, the collector and emitter of each switching transistor being connected in series with a different second impedance means in the order named between said second voltage supply terminal and said first junction; and high-impedance voltage divider means connected between said first and second voltage supply terminals, said voltage divider means having a plurality of taps corresponding in number to the number of said plurality of switching transistors, with different ones of said taps connecting predetermined points on said voltage divider means to the bases of each of said switching transistors, each said switching transistor being rendered conductive when the voltage on the emitter thereof attains a level sufficient to forward bias said switching transistor, the magnitude of impedance of said voltage divider means being substantially greater than the magnitude of impedance of each of said second impedance means.

Claim 5

A gamma control circuit including in combination: first and second voltage Supply terminals for connection across a source of DC supply potential; driver amplifier means, the gain of which is to be controlled, including an amplifier transistor having base, collector and emitter electrodes, the collector of which is connected in circuit with said first voltage supply terminal; means for applying input signals to the base of said amplifier transistor; first impedance means connected in circuit between a first junction coupled with the emitter of said amplifier transistor and said second voltage supply terminal; a plurality of second impedance means; a plurality of switching transistors, each having base, emitter and collector electrodes, the collector and emitter of each switching transistor being connected in series with a different second impedance means in the order named between said second voltage supply terminal and said first junction; and high-impedance voltage divider means connected between said first and second voltage supply terminals, said voltage divider means having a plurality of taps corresponding in number to the number of said plurality of switching transistors, with different ones of said taps connecting predetermined points on said voltage divider means to the bases of each of said switching transistors, each said switching transistor being rendered conductive when the voltage on the emitter thereof attains a level sufficient to forward bias said switching transistor, the magnitude of impedance of said voltage divider means being substantially greater than the magnitude of impedance of each of said second impedance means.

Claim 6

The combination according to claim 3 wherein said amplifier transistor is of one conductivity type and said switching transistors are of an opposite conductivity type.

Claim 7

The combination according to claim 1 further including first and second power supply terminals adapted to be connected across a power supply, wherein the driver amplifier includes an amplifier transistor of one conductivity type having collector, base and emitter electrodes, with the collector electrode of the amplifier transistor being connected in circuit with the first power supply terminal, and with the emitter electrode of the amplifier transistor being connected through the first impedance means to the second power supply terminal, and the switching transistor is of opposite conductivity type to the amplifier transistor with the collector of the switching transistor connected with the second power supply terminal and the emitter of the switching transistor connected through the second impedance means with the emitter of the amplifier transistor, the switching transistor being rendered conductive when the relative potentials applied to the base and emitter thereof forward bias the switching transistor.