PURPOSE: To easily and accurately detect the phase difference between light signal and electrical signal by directly calculating the product of a voltage signal and a light signal by a photoconductive type light receiver and detecting the phase difference from a standardized phase difference value based on a time average value and the intensity value of a current signal.
CONSTITUTION: When a light signal enters a photoconductive type light receiver 110 to which a voltage is applied, a current corresponding to the product of a voltage signal and a light signal flows to the light receiver 110. The current signal is inputted to a current-voltage conversion part 120 to be converted into a voltage signal, and then it is outputted. An LPF 131 outputs a DC voltage by inputting the voltage signal and calculating an time average. On the other hand, an RMS-DC conversion circuit 132 converts the RMS voltage of the voltage signal to a DC voltage, thus outputting a value proportional to the signal intensity of the light signal and voltage signal. Therefore by dividing the time average output from the LPF 131 by a value proportional to the signal intensity using a division circuit 133, a standardized phase difference output which does not depend on the intensity of the light signal and voltage signal can be obtained.
NISHIZAWA MITSUTETSU
KOISHI YU