| 摘要 |
PURPOSE:To obtain the absolute value of a photoelectric current difference, by obtaining an output current from the common collector terminal of two transistors which have bases biased to a common potential and have emitters connected to a pair of photodiode outputs. CONSTITUTION:When a photoelectric current iP2 of a photodiode 12 is increased to become larger than a photoelectric current iP1 of a photodiode 11, the collector current and the voltage between the base and the emitter of a transistor TR14 are increased. Since voltages between bases and emitters of TRs 13 and 14 are equal to each other, collector currents of them are equal to each other. Meanwhile, the photoelectric current iP1 is not changed, and therefore, the emitter current of a TR17 is increased, and a differential current value of photoelectric current is obtained as the sum of collector currents of TRs 17 and 18. Since the differential current is outputted because of the symmetrical circuit even when the photocurrent iP1 is large, the absolute value of the photoelectric current difference is obtained. |
