Patent ID: 7599629
Filing Date: 2009-10-06
Classification: H04B

Abstract:
1. An optical receiver configured to receive optical signals and to convert the optical signals to electrical signals, comprising: a photodiode; an input and an output amplification stage; and an open-loop automatic gain control (AGC) circuit positioned between the input and output amplification stages; the AGC circuit further comprising: a resistor coupled to the photodiode, the resistor configured to receive electrical signals from the photodiode and produce an input optical voltage in proportion to an input optical power level; a comparator configured to compare the input optical voltage with a reference voltage and provide a difference voltage; and a converter coupled to the comparator, the converter configured to receive the difference voltage and output two varying voltages, that vary in opposite directions; and attenuation circuit configured to receive the two varying voltages and output an attenuated electrical signal to the output amplification stage, whereby any fluctuation in the input optical power level is corrected, ensuring a constant output power level, wherein the attenuation circuit comprises a first and a second field effect transistor (FET) that each receives a same one of the two varying voltages and a third FET that receives another of the two varying voltages, the first and second FETs electrically coupling the input and output amplification stages and the third FET electrically coupling nodes between respective source and drain electrodes of the first and second FETs.