| 摘要 |
PURPOSE:To obtain an AGC circuit having a large attenuation, by applying an amplified output to a varactor diode after amplifying an AGC voltage and controlling the attenuation of an input signal in response to the change in the AGC voltage with the capacitance ratio of two capacitance circuits. CONSTITUTION:When the signal input is small and the AGC voltage is low, since a voltage applied to a connecting point A is maximum via an inverting circuit 5, a potential difference across a varactor diode 2 is the highest and its capacitance value is the lowest. Thus, suppose that the capacitance value of the 1st capacitance circuit 1 is set larger than the minimum value of the varactor diode 2, an input signal is outputted to a circuit of the next stage via the circuit 1 without almost being divided. As the AGC voltage increases, the potential difference across the varactor diode 2 is decreased and the capacitance value is increased, then the capacitance ratio of the 1st and the 2nd capacitance circuits 1, 2 is changed, the input signals is attenuated greatly when the varactor diode 2 is the largest, and the signal output to the circuit of the next stage is minimized. |
