Patent ID: 7944249

Claim:
A photoreceiving circuit comprising: a buffer circuit that comprises: a first transistor having a base connected to a first power supply, an emitter as a current signal input node, and a collector as a current signal output node; a second transistor having a base connected to the first power supply; a first constant current circuit using a difference between outgoing current from the emitter of the first transistor and an input current at the current signal input node as a constant current, and determining outgoing current from the emitter of the second transistor as a current same as the constant current; and a first mirror circuit that makes a collector current of the first transistor equal to a collector current of the second transistor, the first mirror circuit having a third transistor with a collector connected to the collector of the first transistor and a fourth transistor with a collector connected to a collector of the second transistor, the buffer circuit being configured such that a first operating point voltage is provided to the current signal output node between the third transistor and the first transistor and a second operating point voltage based on the first operating point voltage is provided to a node between the fourth transistor and the second transistor; a photoreceiving device connected to the current signal input node; and a current-voltage conversion circuit connected to the current signal output node.