PURPOSE:To obtain a feedback type amplifying circuit having an optimum noise index despite a single power supply system by adding a source resistance and a source by-pass capacitor to a field effect transistor. CONSTITUTION:A field effect transistor FETQ contains a feedback resistance Rf and a feedback capacitor Cf. At the same time, a gate resistance Rg is provided between the gate and the earth of the FETQ. Then a source resistance Rs and a source by-pass capacitor Cs are put between the gate and the source of the FETQ. Thus the minus voltage, i.e., the gate bias voltage is generated between the gate and the souece of the FETQ. Thus it is possible to control properly the working point of the FETQ by selecting properly the value of the resistance Rs and then applying the set gate bias voltage to the gate of the FETQ. In such a way, a feedback type amplifying circuit having an optimum noise index can be obtained even when a single power supply system.
展开▼
