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This paper presents a quarter-rate clock and data recovery (CDR) circuit for plesiochronous serial I/O-links. The 2times-oversampling phase-tracking CDR, implemented in 90 nm bulk CMOS technology, covers the whole range of data rates from 5.75 to 44 Gb/s realized in a single IC by the novel feature of a data rate selection logic. Input data are sampled with eight parallel differential master-slave flip-flops, where bandwidth enhancement techniques were necessary for 90 nm CMOS. Precise and low-jitter local clock phases are generated by an analog delay-locked loop. These clock phases are aligned to the incoming data by four parallel phase rotators. The phase-tracking loop of the CDR is realized as a digital delay-locked loop and is therefore immune against process tolerances. The CDR is able to track a maximum frequency deviation of plusmn615 ppm between incoming data and a local reference clock and fulfills the extended XAUI jitter tolerance mask. A bit error rate <10-12 was verified up to 38 Gb/s using a 27 -1 PRBS pattern. With a low power consumption per data rate of only 5.74 mW/(Gb/s) the CDR meets the specifications of the International Technology Roadmap for Semiconductors for 90 nm CMOS serial I/O-links at the maximal data rate of 44 Gb/s. The CDR occupies a chip area of 0.2 mm2.
Date of Publication: July 2009