Fractional rate phase detectors for clock and data recovery

Some recent PLL designs utilize a half-rate phase detector so that the VCO operates at a frequency that is one-half of the input data rate. In this paper, a technique is proposed to extend the half-rate phase detector structure to a rate of 1/2ⁿ, for integer n>1. The concept is explained using a rate 1/8 implementation and simulation results are presented to verify the scheme. These rate 1/2ⁿ phase detectors can be used to raise the maximum operating frequency of clock and data recovery circuits in a given CMOS process technology.