US Patent 7912380 Optical receiver

The present invention provides an optical receiver able to monitor the level of the optical input signal in accurate even when the level is quite small. The optical receiver comprises a photodiode to generate a photocurrent Ipd, a current mirror circuit to reflect the photocurrent into a mirrored current Imon, a current-to-voltage converter to convert the mirrored current Imon to a voltage signal, switch to connect/cut the current mirror circuit with the current-to-voltage converter, and a correction unit for subtracting a signal when the switch is connected from a signal when the switch is cut.