| 摘要 |
PURPOSE:To reduce disturbance light noise with simple constitution and to prevent malfunction by shifting the center frequency of the passing band of a band-pass filter when the signal level of a noise level detection means exceeds a reference level. CONSTITUTION:The output signal (c) of a signal level detection circuit 2 for deciding the detection level of reception signals based on the output signals (b) of the band-pass filter 1 is compared with a reference voltage Vref, a center frequency variable circuit 4 is operated when the level of the output signal (c) becomes higher than the reference voltage Vref, a current to be supplied to the band-pass filter 1 is changed and the center frequency of the band-pass filter 1 is shifted in a direction withdrawing from the frequency of the diffused external light noise. Thus, the amplitude of the disturbance light noise component of the frequency extremely close to the frequency of infrared-ray signals transmitted from a transmitter is effectively reduced and the malfunction by the disturbance light noise is easily improved. |
