| 摘要 |
PURPOSE:To obtain sufficient noise immunity even with a small time constant of a power filter by outputting a noninverting output and an inverting output from an amplifier in response to an electric signal from a photo receiving element and adjusting a potential difference (offset) between the noninverting output and the inverting output. CONSTITUTION:Since the effect of the same noise appears at the noninverting output 21 and the inverting output 22 even when noise, especially noise from a power supply circuit is applied, the effect of noise is cancelled with respect to the identification. Thus, it is possible to prevent the signal from being identified in error. In case of a Si-avalanche photodiode APD or a three-dimension APD especially, although the optimum identification level is not in the center of the signal amplitude but at a lower level from the center of the signal amplitude due to a small dark current end by the shot noise of the APD, the identification level can be set by varying the offset between the noninverting output 21 and the inverting output 22 by an identification level generating circuit 4 against the identification level in this way. Thus, it is not required to use a power filter with a larger time constant. |
