| 摘要 |
PURPOSE:To make negative feedback control stable by controlling a current flowing to a feedback element of a parallel feedback type preamplifier in accordance with a reference signal level in a negative feedback loop comprising the parallel feedback type preamplifier, a current detection path, an error amplifier and a current control element. CONSTITUTION:A current flowing to a feedback element (resistor 6 and capacitor 7) is controlled according to a reference signal level in a negative feedback loop comprising a parallel feedback type preamplifier 2, a current detection circuit 12, an error amplifier 5 and a current control element (FET 3) is controlled according to the reference signal level to keep the output voltage of the parallel feedback type preamplifier 2 constant. Thus, even when the load of the parallel feedback type preamplifier 2 is changed, the control error of the negative feedback loop is minimized to make the negative feedback control stable and even when a photodetection level has fluctuation, an output signal of the constant value is obtained. |
