| 摘要 |
PURPOSE:To suppress the reduction in the reception sensitivity due to noise generated in an electronic circuit and a local oscillation light source by utilizing a pinch-off characteristic of an FET and a gate-source voltage versus drain current characteristic so as to execute the demodulation and weighting simultane ously. CONSTITUTION:A voltage VGS is applied from a power terminal 41 to a gate of a FET 46 of demodulation weighting circuits 29, 33 via resistors 43, 45 and a voltage VDS is applied from a power terminal 42 to the drain via resistor 44. The bias is selected by selecting the voltage VGS and the resistors 43, 45 so as to attain the relation of gate-source voltage VGS=pinch-off voltage Vp in the operation of the FET 46. In giving an input waveform whose amplitude is 2E or whose amplitude is 2alphaE in this state, the input is rectified and amplified to obtain an output waveform whose amplitude is I or alpha<2>I. Thus, the synthesis with a maximum ratio is attained, resulting in that the deterioration of the reception sensitivity due to noise generated in the local oscillating light source and an electronic circuit (including photodetector) is suppressed. |
