| 摘要 |
PURPOSE:To control an amplification signal to be in little distortion by keeping the bias of a bias control pole constant and altering the electric potential of a source or an emitter. CONSTITUTION:In order to make the voltage VGS between a gate and the source zero V, a G point and the source S are set in the same electric potential by a resistance RG and an FET always executes an A-grade amplifying action. An automatic gain control electric potential VAGC is supplied to the source side so as to alter the voltage VDS between a drain and the source. If a large amplitude input is introduced in a circuit, the VAGC is automatically increased by feedback and a current flows in the resistance RS. Then a source electric potential VS rises and the VDS is decreased. And the gain lowers, so that a signal output in an amplification limit is outputted. Thus, an output wave with little distortion can be obtained by lowering the gain corresponding to the large amplitude input wave.
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