Bias circuit for photodiode.

摘要

In order to reduce a change in reverse bias to a photodiode due to drift of a power supply caused by, e.g., noise, and to suppress generation of a wrong photoelectric current detection signal, a bias circuit includes a load element (4), a transistor (Q1) for receiving a current from the load element (4) at its collector, a transistor (Q2) constituting a current mirror circuit together with the transistor (Q1), a level shift circuit connected between the base of an output transistor (Q3) of the current mirror circuit and the collector of the transistor (Q1), and constituted by transistors (Q4 - Q7) and load elements (R1 - R4), and a photodiode (1) connected to a desired potential node of the level shift circuit.