| 摘要 |
PURPOSE:To make it possible to make an operation reliable and to simplify a circuit construction by a method wherein a reference voltage being supplied and varying on a time basis is compared with an input signal voltage of each of a plurality of channels in a comparator for each channel. CONSTITUTION:An input photocurrent signal from a light-sensing element S1 to S6 for each channel is converted into a voltage signal by an operational amplifier in a first stage and passed through a capacitor and only the high-frequency component thereof is amplified by an operational amplifier in a subsequent stage. In a reference voltage generating device 30, reference voltages V11 to V16 varying in accordance with distances of the elements S1 to S6 from a subject are generated from a voltage of a constant-voltage circuit 31 by switching of a transistor 32 and resistances r1 to r6 for voltage division. An input signal voliage and the reference voliage V11 to V16 are compared with each other by a comparator 28a to 28f provided for each of the elements S1 to S6 and an inverted output signal A1 to A6 of the output terminal of the converter is detected. At the time point when a prescribed number of signals are detected, the remainder is made ineffective, and a prescribed number of signal voltages corresponding to voltage levels are selected from a plurality of them. |
