| 摘要 |
PURPOSE:To attain suppression of fluctuation of a control voltage and to attain high speed response by providing a high pass filter having a cut-off characteristic in a feedback loop generating a gain control voltage corresponding to an output signal amplitude of an automatic gain control circuit and controlling the gain corresponding to the amplitude of an output signal of the high pass filter so as to reduce the time constant of a smoothing circuit. CONSTITUTION:The high pass filter comprising capacitors 6, 7 and resistors 8, 9 has a cut-off characteristic of 6dB/DCT at a cut-off frequency 1/2piRCHz, where C is capacitance of the capacitors 6, 7 and R is the resistance of resistors 8, 9. A rectifier 4 applies full-wave rectification to an output signal of the high pass filter 11 and the smoothing circuit 3 smoothes the rectified signal. An operational amplifier OPA2 gives a signal proportional to a voltage difference between the smoothed signal being the output signal of the smoothing circuit 3 and the voltage of a reference power supply 5 to a gain control terminal of a voltage gain amplifier GCA1. The automatic gain control circuit AGC acts like making the output signal of the smoothing circuit 3 equal to the voltage of the reference power supply 5. |
