| 摘要 |
PROBLEM TO BE SOLVED: To provide a light-receiving circuit capable of accurately removing not only noises mixing with a laser beam, but also mixing noises having different levels. SOLUTION: A current signal, which is photoelectric-converted by a first and a second photodiodes 11, 12, is converted into a voltage signal by a fixed resistor 17 and a variable resistor 27 and is inputted into a differential amplifier 29. A voltage signal which is equivalent to a normal laser beam is multiplied by the amplifier 29 to be normally outputted, and a voltage equivalent to a noise, having a noise level of the same phase and the same level mixed in the laser beam, is eliminated by the circuit 29. Noise, having a different level mixed into the outputs of the photodiodes 11, 12, is removed surely by adjusting a voltage different from the normal voltage equivalent to this noise by the resistor 27.
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