| 摘要 |
PURPOSE:To easily remove an amplitude noise through an electric circuit behind a photodetector by detecting a light signal by an avalanche photodiode during optical reproduction, detecting variation and feeding it back to a power source negatively, and controlling an operating bias to the avalanche photodiode. CONSTITUTION:A specific reverse bias voltage is impressed from a DC-DC converter 31 to the cathode of the avalanche photodiode 28 and an output signals corresponding to a light signal from the anode side is supplied to and amplified by a head amplifier 32. This amplified information signal is supplied to a limiter 33 to perform amplitude control, and part of the information signal is supplied to a DELTAP detector 34 to perform envelope detection, detecting variation of the information signal. This detection signal is fed back to the DC-DC converter 31 negatively through a smoothing circuit 35 and its output voltage, i.e. reverse bias voltage is controlled according to the variation. The avalanche photodiode 28 varies in amplification factor with the reverse bias voltage, so when the variation is large in amplitude, the amplification factor is decreased by lowering the reverse bias voltage and the level of the conversion output drops. |
