To provide a signal detecting circuit for a rain sensor equipped with an external light reducing circuit made possible to reduce external light by electrical processing.
The signal detecting circuit for the rain sensor is constituted so that the windowshield of a vehicle is irradiated with pulse light from an LED in order to automatically control a wiper for excluding raindrops on the windshield of the vehicle and the reflected light from the windshield is detected by a PD while the pulse signal from the LED is processed to be inputted to an operational processor. This signal detecting circuit is equipped with a current-voltage conversion circuit 24 for converting the pulse signal from the LED 10 to a voltage signal, the external light component reducing circuit 42 provided in parallel to the current-voltage conversion circuit 24 and holding the definite external light component contained in the output signal of the current-voltage conversion circuit to feed back the same to the inlet side of the current-voltage conversion circuit and a band pass filter circuit/amplifying circuit 26 for reducing the noise of the output signal of the current-voltage conversion circuit to amplify the output signal.
IGUCHI KEITARO
MAKINO YOSHIAKI
Takeshi Nakamura