Low-jitter, plain vanilla CMOS CDR with half-rate linear PD and half rate frequency detector

摘要

This paper presents a dual loop Clock and Data Recovery (CDR) circuit for high-end, low data rate, wireless transfer (100-200kb/s). Firstly, design tradeoffs for the single loop variant of the CDR are formulated which include jitter transfer (JT) function in frequency domain and long term jitter in time domain. These design rules are then used for the realization of a dual loop CDR consisting of tristate half rate frequency detector (FD), half rate linear phase detector (PD), bootstrapped current switch charge pump (CP) and ring based 4-phase VCO. All building blocks (except CP) are realized with plain vanilla CMOS digital circuits. In the proposed design, the output of the tri-state FD is zero when in lock and has no contribution to VCO jitter. In addition, the linear PD yields zero phase difference under the same lock condition. As a consequence, the CDR circuit can work with low jitter for low power applications.