| 摘要 |
PURPOSE:To make the circuit operation stable with no adjustment, by providing a switch circuit sonstituting with differential pair transistor (TR) to an output side of a differential amplifier so as to change one of control signals to an avalanche photodiode and a varable gain control circuit in response to an output voltage of the amplifier. CONSTITUTION:The variable gain control circuit is provided with the avalanche photodiode APD receiving an optical signal, a variable gain control amplifier AGCA to which the output of the APD is applied and a post-stage amplifier PSA. A feedback circuit comprising a peak detector PD, a comparison amplifer OPA, a switch SW and a control converter DC-DC is connected to the amplifier PSA. The switch SW is provided with DFT1, DFT2 of a differential pair comprising TRs Q5-Q8 and the bases of the TRs Q6-Q7 are connected in common. Further, one of output voltages V2, V3 applied to the converter DC-DC and the amplifier AGCA is changed depending on the relation between an output voltage V1 of the amplifier DPA and a reference voltage Vth and the circuit operation is made stable without any adjustment. |
