Fractional Rate Phase Detectors for Clock and Data Recovery

Overview

The use of optical fiber as a transmission medium in communications networks allows very high bandwidth to be achieved. However, dispersion effects within the fiber require that the data be regenerated periodically. Optical links typically convert from the optical domain to the electronic domain to perform the regeneration and then reconvert the signal back into the optical domain for subsequent transmission. In the receiver front-end, clock information is required for synchronized sampling such that the value of the input signal is sampled at the optimum time. They show a generic Clock and Data Recovery (CDR) circuit that is based on a charge pump Phase-Locked Loop (PLL).