CURRENT AMPLIFYING CIRCUIT

PURPOSE:To eliminate a dark current and to control an auto bias level by obtaining a DC direct-coupled constitution. CONSTITUTION:Current mirrors are composed of npn type transistors Q1 and Q2 pnp type transistors Q3 and Q4, Q5 and Q6 respectively. Provided that, the emitter area of the Q6 is (n) times as large as the emitter area of the Q5, and the n-fold current of the current of the Q5 flows to the Q6. The current to flow to the Q1 goes to be equal to a direct current component of the current to flow from the emitter of a phototransistor Q0. Since the current equal to this flows from the Q4 to the collector of the Q0, the current to flow from the Q5 to the collector of Q0 goes to be equal to the alternating current component of the current to flow to the Q0. When the current of the Q5 is made n-fold and taken out from the Q6, only a signal current of the current to flow to the phototransistor Q0 can be n-fold and taken out to a terminal I0.