Gain-controlled amplifier

Details Gain-controlled amplifier Gain-controlled amplifier

1982-08-13

1984-05-29

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including differential amplifier

330279, 330 85, H03F 345, H03G 320

Patent

active

044517980

ABSTRACT:
A gain-controlled amplifier having a gain which varies exponentially with a control voltage magnitude applied thereto comprises first and second transistor pairs, a driver circuit, a feedback circuit and a subtraction circuit. The first transistor pair comprises first and second transistors, and the second transistor pair comprises third and fourth transistors, all of the transistors being of the same conductivity tape. The emitters of the respective transistor pairs are joined together, the bases of the first and third transistors and the bases of the second and fourth transistors are joined together, respectively, and the two joined bases serve as input terminals of a control voltage. The driver circuit drives each of the joined emitters in opposite phase relation to each other in accordance with an input signal of the amplifier, the gain of the amplifier being controlled by the control voltage magnitude. A difference of the collector currents of the respective first and third transistors is used to effect a negative feedback of the amplifier, while a difference of the collector currents between the respective second and fourth transistors is used to deliver an output signal of the amplifier through the subtraction circuit.

REFERENCES:
patent: 4396891 (1983-08-01), Johansson et al.

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