| 摘要 |
<P>PROBLEM TO BE SOLVED: To improve a malfunction and a decrease in a range under an inverter fluorescent lamp or the like. <P>SOLUTION: A head amplifier 2 converts the light receiving current of a photodiode 1 to a voltage and amplifies it, a gain control circuit 4 amplifies the output signal from the amplifier, a limit amplifier 5 performs limit amplification of the output signal from the circuit 4, and a bandpass filter 6 extracts a carrier frequency component. A detector 7 detects a disturbance noise component, controls the Q value and gain of the bandpass filter 6 on the basis of its detection result, and controls the gain of the gain control amplifier 4. An integrator 10 converts the carrier frequency component obtained by the bandpass filter 6 into a PWM signal, a comparator 11 shapes its waveform, and an output circuit 12 outputs the relevant signal to the output terminal 14 of the collector of a transistor 13. <P>COPYRIGHT: (C)2004,JPO |
