A 4×40 Gb/s quad-lane CDR with shared frequency tracking and data dependent jitter filtering

Abstract

A 4×40 Gb/s collaborative digital CDR is implemented in 28nm CMOS. The CDR is capable of recovering a low jitter clock from a partially-equalized or un-equalized eye by using a phase detection scheme that inherently filters out ISI edges. The CDR uses split feedback that simultaneously allows wider bandwidth and lower recovered clock jitter. A shared frequency tracking is also introduced that results in lower periodic jitter. Combining these techniques the CDR recovers a 10GHz clock from an eye containing 0.8UIpp DDJ and still achieves 1-10 MHz of tracking bandwidth while adding <; 300fs of jitter. Per lane CDR occupies only .06 mm2 and consumes 175 mW.