US 3,942,181 A · Variable-gain amplifier

Abstract

A variable-gain amplifier comprises a transistor with an emitter connected in a degenerative emitter-follower circuit which includes a PIN diode traversed by a current injector in the form of an operational amplifier, the PIN diode forming part of a negative-feedback path extending from the output to the inverting input of the operational amplifier. To achieve a gain characteristic whose logarithm varies linearly with a control voltage, this control voltage is fed to the same inverting input through an amplifier circuit with an exponential characteristic, including another operational amplifier provided with an input transistor. A temperature-compensating circuit, preceding that input transistor, comprises still another operational amplifier having a further transistor inserted in its negative-feedback path. The variable-gain amplifier may be included in one of two conjugate (sum and difference) channels of a monopulse radar.

Claims10

Dependent claims

A variable-gain amplifier comprising:

semiconductor means provided with an input electrode connected to a source of high-frequency signals and with two further electrodes including a reference electrode whose potential relative to that of said input electrode determines the conductivity of said semiconductor means, one of said further electrodes being connected to a load;
degenerative circuitry connected to said reference electrode for applying thereto a negative-feedback voltage;
a PIN diode in said degenerative circuitry;
biasing means for said PIN diode including an operational amplifier provided with an inverting input, a non-inverting input, an output, and a negative-feedback path connected between said output and inverting input thereof, said PIN diode being inserted in said negative-feedback path;
and
a source of gain-controlling voltage connected to one of the inputs of said operational amplifier.

3 more elements

Dependencies are inferred from the claim text.

Variable-gain amplifier

Life of this patent

Variable-gain amplifier

Life of this patent

Abstract

Claims10