| 摘要 |
PURPOSE:To reduce the variance of an output signal level due to noise, by controlling a bias voltage of photoelectric conversion element according to the amplitude of a DC component of an optical input signal. CONSTITUTION:A control means consisting of a DC/DC converter 14 having a constant output voltage is used for an input voltage having a constant value or more, voltage monitor circuit 34 and voltage controlled switch 32 are used. When the amplitude of an optical input signal is small, the AGC operation is made by detecting the DC component of the optical input signal through the use of a smoothing circuit 24 without peak detection, and the AGC operation by the peak detection is made if the amplitude of the optical input signal is greater, that is, the S/N is good, then the amplitude of the output signal can be avoided from being smaller than the specified value through noise, if the amplitude of the optical input signal is small and the S/N is worse. |
