| 摘要 |
PURPOSE:To enhance distance measuring capacity, by dividing an amplifier for amplifying a detection signal into an input stage and an output stage and setting the input stage to a constant gain due to a fixed bias and allowing the output stage to depend on the output of the amplifier to make a bias current variable. CONSTITUTION:The emitter resistors R1, R2 of the transistors (Tr) Q1, Q2 of the input stage of a gain variable amplifier 4 are connected to a constant current circuit LL and the currents I 15, I 16 flowing to the current supply Tr Q15, Q16 connected to a current mirror become the emitter currents of Tr Q5, Q6 of the output stage of the same amplifier as the control signals to amplifiers 4, 5 to perform the gain control of the respective amplifiers. The output current Ip at the output point Po of the amplifier 4 is inputted to one terminal of a current/voltage converter circuit 6 and the output of the circuit 6 is fed back to one terminal of the circuit 6 through a feedback resistor R6. Further, the amplifier 5 for obtaining the difference signal necessary for measuring a distance is constituted in the same way as the amplifier 4. Therefore, the dynamic range relating to the output change at the point Po becomes wide and the erroneous measurement of a distance due to disturbance light is removed. |
