Miles & Stockbridge P.C.
Variable gain amplifier
A variable gain amplifier of such configuration that can yield continuously and log-linearly variable gains in relation to control voltage and, at the same time, that does not use an attenuator, an element which otherwise would entail cause of increased noise. The amplifier includes a plurality of gm amplifiers connected in parallel with input signal, exponential multipliers connected respectively to the gm amplifiers, a control section to vary the multiplication coefficient of the exponential multipliers according to the external gain control signal, and an I-V converter circuit to aggregate current output after multiplication and convert the aggregated current output to voltage. A continuously variable gain characteristic can be obtained without the use of an attenuator but by varying multiplication coefficient according to control voltage.
Hitachi, Ltd.
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Hiroyasu Satoshi
Yoshizawa Hanazawa