| 摘要 |
PURPOSE:To obtain a linearizing signal having a wide linear range by arranging a nonlinear element converting a gain control variable in a form of a linear electrical signal into a circuit constituting an AGC negative feedback loop in applying AGC. CONSTITUTION:An AGC amplifier 1 suppresses a level fluctuation of a high frequency signal generated attended with fluctuation of an electric field strength of a received wave and outputs an output signal of a prescribed level as a variable gain amplifier. An output signal amplified by the AGC amplifier 1 is inputted to an AGC control section 2 and converted into a form of a DC voltage by a detection circuit and a filter. Then the converted DC voltage is compared with a prescribed reference voltage,and the result of comparison is outputted in a form of a voltage at a point Q as an AGC control signal (a). The AGC control section 2 uses the outputted AGC control signal (a) to control the negative feedback loop comprising a resistor R1, a transistor (T)1 and the AGC amplifier 1 for the AGC and applies current/voltage conversion to generate a linearized signal (6) shown in figure at a point P via resistors R1, R2, the TR1 and a diode D1. |
