| 摘要 |
PURPOSE: To easily and surely eliminate the offset by less processing. CONSTITUTION: A multi-element photodetector 5 has many photodetectors arranged and converts an inputted optical signal to an electric signal and outputs this signal. The offset level of each photodetector is inputted as a digital signal from an offset level input part 1 and is held in an offset level holding circuit 2. In accordance with the control signal from a control circuit 6, offset levels held in the offset level holding circuit 2 are converted to analog signals by a D/A conversion circuit 3 and are inputted to an analog subtraction circuit 4, and the output from the multi-element photodetector 5 is inputted to the analog subtraction circuit 4. This circuit 4 subtracts the output of the D/A conversion circuit 3 from the output of the multi-element photodetector 5 and outputs the result. |
