| 摘要 |
PURPOSE:To improve the stability of amplification by adding an external circuit with variable impedance to a common-emitter type variable gain amplifying circuit. CONSTITUTION:Loads Z1 and Z2 including the variable impedance element of common-emitter type amplifying circuit 1 are brought under the control of control circuit 2. To the base of the transistor of amplifying circuit 1, PIN diode D1 and resistance R1 is connected as external circuit 6 and control circuit 7 controls the impedance of diode D1. In high-gain operation, the impedance of diode D1 decreases and as low-gain operation changes from the above-mentioned state, the impedance of diode D1 increases. As a result, the lowering of the gain of external circuit 6 increases to facilitate the lowering of the gain of a high-frequency part, where the increase of the gain of amplifier circuit 1 is canceled, so that the stbility of the operation can be improved. |
