| 摘要 |
PURPOSE:To eliminate influence of external noises in demodulating a photo signal by using the active impedance of an active element for the load circuit of a photoelectric converter element. CONSTITUTION:When direct-current light strikes photo diode 1, part of a photo current flows from the base to emitter of transistor 11 via resistance 9 to become the base current of transistor 11. At this time, since a current equivalent to that obtained by multiplying the current to resistance 9 by current amplification factor beta of transistor 11 flows to the collector of transistor 11, the load impedance of photo diode 1 decreases down to approximately one beta-th against the direct-current light. Therefore, saturation never occurs until direct-current light of intensity beta times over, so that the dynamic range will widen. When a photo signal modulated by a frequency in the ultrasonic range strikes photo diode 1, transisitor 11 becomes cut off, thereby obtaining high impedance. |
