A 6.5-12.5-Gb/s Half-Rate Single-Loop All-Digital Referenceless CDR in 28-nm CMOS

This article presents a novel method for frequency tracking based on an extended bang-bang phase detector (XBBPD) in a referenceless clock and data recovery (CDR) circuit. The XBBPD-based structure has a frequency tracking range that completely covers the tuning range of the digitally controlled oscillator (DCO) with a fast locking feature. To minimize the loop delay and thereby improve the jitter tolerance, the CDR design includes an additional proportional path that is realized by directly controlling the phase of the oscillator with the output signal of the phase detector. The design is all-digital, including digital filters that simplify the design. The CDR occupies an active area of 0.031 mm2, implemented in a 28-nm CMOS process. The receiver operates up to 12.5 Gb/s. The frequency locking time, measured as the time required for every 1-Gb/s change in the input data, is 320 ns. The power consumption is only 21.13 mW, corresponding to an energy efficiency of 2.11 pJ/bit.