| 摘要 |
PURPOSE:To improve the residual noise characteristic of a voltage gain control circuit by using DC feedback so as to suppress the fluctuation of an output DC voltage attended with the gain control. CONSTITUTION:An input signal is converted into a current I by a transistor (TR) Q3. The current I is branched by TRs Q1, Q2. A DC feedback circuit 1 is connected to the TR Q2. The DC feedback circuit 1 compares the signal output with a reference voltage to make the collector voltage of the TR Q2 constant so that the output DC level is always constant. Through the constitution above, the generation of noise due to excess circuits is eliminated and the gain is decreased and then the noise is decreased.
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