| 摘要 |
PURPOSE:To input stable distortion-free signals to a digital delay detecting means by providing an automatic gain controller which AC-amplifies the output signal of a phase detector and controls the gain of a high-frequency amplifying means based on the AC-amplified output signal. CONSTITUTION:An automatic gain controller AGC is a circuit which controls the output of a high-frequency amplifier 10 to maintain the input signal of an A/D converter 30 at a fixed level and is constituted of a peak detector 11 which detects the peak value of the output of an operational amplifier 27 at a time constant longer than beats and a comparator 12 which raises the gain of the amplifier 10 when the peak value is lower than a prescribed level and lowers the gain when the peak value is higher than the prescribed level. While the input of the peak detector 11 of the controller AGC is obtained from one of AC amplifiers which output orthogonal base band signals, the output of either AC amplifier is used when their gains are equal. |
