| 摘要 |
An amplifier 11 to which transistors 13 and 14 functioning as variable resistors are connected in parallel is used. A burst signal is received by a light receiving element 10 and the received signal is converted into an input current signal Iin. The input current signal Iin is converted in the amplifier 11 into an output voltage Vo. Determination is made in a determining circuit 20 as to whether the output voltage Vo exceeds a current voltage V 1 which is a threshold. The result of determination is stored in a register circuit 15 . Based on the result of determination outputted from the register circuit 15 , a desired voltage is selected from among a number of voltages generated beforehand in a control voltage generating circuit. The selected voltage is used to generate a control voltage Vg 1 or Vg 2 to be applied to the transistors 13 and 14 ; and the generated control voltage Vg 1 or Vg 2 is inputted to the transistor 13 or 14 of the amplifier 11. |
