| 摘要 |
PURPOSE:To make a pilot signal, etc., needless to simplify a circuit constitution by detecting the DC light level in a light receiving unit and giving AGC. CONSTITUTION:The receiving signal of photo diode 1 is subjected to wideband amplification in 7 and is supplied to control circuit 8. Circuit 8 attenuates the input signal by a quantity corresponding to the control signal voltage and outputs the input signal, and an output signal is obtained through amplifier 4. At this time, the output DC voltage of circuit 8 is compared with reference voltage Es by control voltage generation circuit 9, and error components between both voltages are amplified and are applied to circuit 8 as a control voltage. Consequently, the output DC level of circuit 8 becomes always fixed for change of the input level. |
