| 摘要 |
PURPOSE:To reduce an offset by compensating it automatically by providing two light receiving elements and a third arithmetic circuit to calculate the difference of the outputs of a first and a second arithmetic circuits. CONSTITUTION:Two light signals incident to a photodetector 1 are converted into electric signals by the light receiving elements 2a and 2b, and are amplified by phase inverting type pre-amplifiers 3a and 3b, and the outputs of the circuits 3a and 3b are subtracted by the arithmetic circuit 4. Besides, the output peak values of the circuits 3a and 3b are detected and held by peak hold circuits 5a and 5b, and the outputs of the circuits 5a and 5b are subtracted by the arithmetic circuit 6, and further, the outputs of the circuits 4 and 6 are subtracted by the arithmetic circuit 8. Thus, an offset component remaining in the difference of the light signal outputs is removed by subtracting the difference of the non-signal outputs of the light receiving elements 2a, 2b from the difference of the light signal outputs of the light receiving elements 2a, 2b. |
