| 摘要 |
PURPOSE:To obtain a stable output amplitude at all times, by providing a switching circuit between an amplitude detection circuit and an error signal generating circuit, switching it with an input signal of a gain variable circuit and generating a constant error signal at no signal input. CONSTITUTION:A signal detection circuit 7 is operated at no signal, a switch circuit 9 is changed over from Ito II through a delay circuit 8, and a voltage of a reference voltage source 10 is applied to an error signal generating circuit 5. In this state, the output amplitude of a circuit 2 is independent of the input, the gain is determined with the source 10 and set to prescribed value. At signal input state, the circuit 7 is operated, the circuit 9 is switched from IIto I through the circuit 8 and the circuit 2 is operated to be a prescribed output amplitude with an amplitude detection circuit 3 and the circuit 5. In this case, the voltage source 10 activates the circuit 5 until the detected voltage level of the circuit 3 reaches a prescribed level with the time constant of CR so that the circuit 5 outputs a stable error signal independently of the presence/absence of signals. Thus, the CR time constant can be set large and the stable output can be obtained. |
