Method and system for compensation of low-frequency photodiode current in a transimpedance amplifier

摘要

A method and system to compensate for DC and low frequency current produced by a photodiode that is illuminated with an optical data stream is described. An optical data stream ideally produces no current from a photodiode when the bit is a 0 and produces a current proportional to the optical power when the bit is a 1. Thus, the current produced from the photodiode consists of a DC component, which is typically half the current of a 1 bit (if there is an equal number of 1s and 0s in the data), and a high frequency component that carries the data. The DC component can interfere with the signal path's ability to process the information carrying component of the photodiode current, by causing a fixed offset to propagate and be amplified through it. This offset distorts the voltage signal at the output of the signal path, and must therefore be cancelled early in the path; usually in the first transimpedance stage or just after it. The technique described here performs this neutralization at the output of the first transimpedance amplifier stage.