Patent ID: 7394994

Claim:
An optical receiver circuit comprising: an optical converter circuit to convert optical power into electrical power; a sensor circuit connected to the optical converter circuit, the sensor circuit to detect and output a characteristic value of the electrical power; and an attenuator circuit comprising a variable attenuation, the variable attenuation dependent on the characteristic value of the electrical power output by the sensor circuit, wherein the attenuator circuit is configured to provide a constant output signal level of the optical receiver circuit; wherein the attenuator circuit comprises a step attenuator circuit comprising: a plurality of cascaded attenuator stages, wherein each of the continuing stages comprises two resistors and a semiconductor switch in series with the resistors and another semiconductor switch connected to bridge one of the resistors; and capacitors to separate respective input ends of the attenuator stages, an input capacitor to connect an input end of the attenuator stages to an output of the optical converter circuit, and an output capacitor to connect an output of the attenuator circuit to a load impedance.