Optical receiver

Abstract

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.

1 - 16 . (canceled) 
   
   
       17 . An optical receiver including a power monitoring circuit for outputting a monitoring signal corresponding to a photocurrent generated by a photodiode by receiving an optical signal with an optical level, the optical receiver comprising:
 a current mirror circuit connected to the photodiode, the current mirror circuit generating a mirrored current by receiving the photocurrent;   one current-to-voltage converter provided in the power monitoring circuit for converting the mirrored current into a first voltage signal with a substantial offset when the variable conversion gain of the current-to-voltage converter is set to a first gain, and for converting the mirrored current into a second voltage signal with the substantial offset when the variable conversion gain of the current-to-voltage converter is set to a second gain different from the first gain; and   a correction unit for subtracting the first voltage signal from the second voltage signal to cancel the substantial offset of the current-to-voltage converter.   
   
   
       18 . The optical receiver according to  claim 17 , wherein
 the current-to-voltage converter is a trans-impedance amplifier including an inverting amplifier and a resistor connected between input and output terminals of the inverting amplifier, the inverting amplifier having the substantial offset, and   the first gain of the current-to-voltage converter is obtained by setting the resistor to a first resistance and the second gain of the current-to-voltage converter is obtained by setting the resistor to a second resistance.   
   
   
       19 . The optical receiver according to  claim 17 , wherein
 the current-to-voltage converter includes a resistor and a voltage follower, the mirrored current flowing in the resistor and the voltage follower detecting a voltage drop induced in the resistor due to flowing of the mirrored current, and   the conversion gain of the current-to-voltage convertor is set by changing the resistance of the resistor.   
   
   
       20 . A method for monitoring an input optical level of an optical signal received by an optical receiver, the method comprising the steps of:
 converting the optical signal into a photocurrent by a photodiode;   reflecting the photocurrent into a mirrored current by a current mirror circuit;   converting the mirrored current into a first voltage signal with a first conversion gain by one current-to-voltage converter with a substantial offset;   converting the mirrored current into a second voltage signal with a second conversion gain by the one current-to-voltage converter; and   subtracting the second voltage signal from the first voltage signal to cancel the substantial offset of the one current-to-voltage converter.   
   
   
       21 . The method of  claim 20 , wherein
 the one current-to-voltage converter includes an inverting amplifier with the substantial offset and a feedback resistor connected between an input terminal and an output terminal of the inverting amplifier, and   the first and second conversion gains of the one current-to-voltage converter are set by varying the resistance of the feedback resistor.