| 摘要 |
PURPOSE:To prevent the invasion of noise to a feedback circuit by using photodetection diodes connected in anti-series connection for a changeover switch so as to change over a feedback resistor. CONSTITUTION:A changeover switch has a structure in anti-series connection of PIN photodiodes and electrodes alpha, beta are used for both electrodes of the switch. LEDs 7, 8, 9 are provided to positions opposite to the photodetection diodes 4, 5, 6, a light beam is radiated to the photodetection diodes 4, 5, 6 by driving the LEDs 7, 8, 9 to drive the switch thereby applying gain adjustment through the changeover of the combination of feedback resistors R1, R2 and R3. The operation of the changeover switch is applied by transmitting/receiving an optical signal and no electric contact exists with the changeover switch, then noise invasion to the feedback circuit through switch in the case of a conventional amplifier is prevented.
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