| 摘要 |
PURPOSE:To obtain a gain circuit with low noise and a low distortion factor, by providing a means which varies a circuit bias current automatically corresponding to the level of an input signal in addition to a variable gain function part. CONSTITUTION:The input signal of an input terminal 11 is supplied to a transistor(Tr)13 via a resistor 12, and also is supplied to a voltage-current converter 33. A voltage applied on the terminal 11 is converted to a current by the converter 33, and full wave rectification is applied at a full wave rectifier circuit 32. A rectified output is mixed with the output current of a constant current source 31, and its output current is distributed to Trs 13, 14, 18 and 19, and a current mirror circuit 34 by a current distributor 28. In such constitution, since the output current of the circuit 32 is decreased when a signal level is low, and thereby, the output current of an adder 30 is decreased, and the output current of the distributor 28 is also decreased, the noise of the circuit is decreased, and an S/N can be improved. Also, when the input signal applied on the terminal 11 is large, the output currents of the circuit 32, the adder 30, and the circuit 28 are also increased, and the dynamic range is increased, thereby, distortion can be reduced.
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