Circuit with electrically controlled gain

Details Circuit with electrically controlled gain Circuit with electrically controlled gain

1979-03-26

1981-02-17

Mullins, James B.

Amplifiers

With semiconductor amplifying device

Including gain control means

330288, 330289, H03G 330

Patent

active

042517788

ABSTRACT:
A gain control circuit includes a first transistor with direct-coupled collector-to-base feedback converting current, applied to its collector, to logarithmically related voltage appearing between its emitter and base. This logarithmically related voltage is incremented or decremented by a voltage .DELTA.V.sub.1 proportional to T and applied to the emitter-base junction of a second transistor used as a logarithm of voltage to current converter, T being an absolute temperature close to that at which the first and second transistors are operated. .DELTA.V.sub.1 is developed as the potential drop across a resistive element R1, responsive to the output current of a current-to-logarithm-of-current converter circuit, making the conversion with a scaling factor proportional to T divided by the resistance R.sub.1 of resistive element R1. Accordingly, the gain setting of the gain control circuit is unaffected by change in T.

REFERENCES:
patent: 3828266 (1974-08-01), Okada et al.
patent: 4055774 (1977-10-01), Ahmed

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