All-digital half-rate referenceless CDR with single direction frequency sweep scheme using asymmetric binary phase detector

摘要

This paper presents an all-digital half-rate referenceless CDR with a single direction frequency acquisition achieved. Thanks to asymmetric binary phase detector (ABPD), compared with existed inverse alexander phase detector (IAPD), we changed the input-output characteristic to enable accumulated phase error point in the same direction when frequency error happens while the output of IAPD has no directivity. Once the frequency of the digital controlled oscillator (DCO) enters the pull-in range of the CDR loop, the phase is automatically locked. To improve jitter tolerance (JTOL) performance further, IAPD logic is enabled, and ABPD is disabled after locking. The prototype was implemented in a 28 nm low power CMOS process with a data rate tracking range of 9–11 Gb/s. The measured JTOL is 0.35 UI at high frequency with PRBS31 input data pattern.