US 3,940,708 A · Gain control circuit

Abstract

A gain control circuit of the balanced type whose gain is linearly controllable over a wide range and wherein the DC level at the circuit output is maintained at a constant value regardless of variations of the controlling current. The gain control circuit is comprised of a first differential amplifier which receives an input signal differentially applied thereto, and a second differential amplifier connected in series with the first differential amplifier. Unidirectional conductors are connected to the outputs of the first differential amplifier as a load impedance and variable currents are supplied to the first differential amplifier outputs to control the currents flowing in the unidirectional conductors and thereby vary the load impedances presented by the unidirectional conductors. The amplified output signal is derived from an output of the second differential amplifier.

Claims11

Dependent claims

A gain control circuit, comprising:

first differential amplifier means coupled to a first constant current source, said first differential amplifier means having input means for receiving an input signal differentially applied thereto and output means;
second differential amplifier means coupled to a second constant current source, said second differential amplifier means having input means connected to said first differential amplifier output means and output means for producing an amplified output signal;
unidirectional conducting means connected to said first differential amplifier output means as load impedance therefor;
and
means for supplying a variable current to said first differential amplifier output means to control the current flowing in said unidirectional conducting means and thereby vary the load impedance presented by said unidirectional conducting means.

2 more elements

Dependencies are inferred from the claim text.

Gain control circuit

Life of this patent

Gain control circuit

Life of this patent

Abstract

Claims11