4-Cycle-Start-Up Reference-Clock-Less Digital CDR Utilizing TDC-Based Initial Frequency Error Detection with Frequency Tracking Loop

This paper proposes a reference-clock-less quick-start-up CDR that resumes from a stand-by state only with a 4-bit preamble utilizing a phase generator with an embedded Time-to-Digital Converter (TDC). The phase generator detects 1-UI time interval by using its internal TDC and works as a self-tunable digitally-controlled delay line. Once the phase gen-erator coarsely tunes the recovered clock period, then the residual time dif-ference is finely tuned by a fine Digital-to-Time Converter (DTC). Since the tuning resolution of the fine DTC is matched by design with the time reso-lution of the TDC that is used as a phase detector, the fine tuning completes instantaneously. After the initial coarse and fine delay tuning, the feedback loop for frequency tracking is activated in order to improve Consecutive Identical Digits (CID) tolerance of the CDR. By applying the frequency tracking architecture, the proposed CDR achieves more than 100 bits of CID tolerance. A prototype implemented in a 65 nm bulk CMOS process operates at a 0.9-2.15 Gbps continuous rate. It consumes 5.1-8.4 mA in its active state and 42 mu A leakage current in its stand-by state from a 1.0 V supply.