A 4x32Gb/s 1.8pJ/bit Collaborative Baud-Rate CDR with Background Eye-Climbing Algorithm and Low-Power Global Clock Distribution

Abstract

This paper presents design techniques for an energy-efficient multi-lane receiver (RX) with baud-rate clock and data recovery (CDR), which is essential for high-throughput low-latency communication in high-performance computing systems. The proposed low-power global clock distribution not only significantly reduces power consumption across multi-lane RXs but is capable of compensating for the frequency offset without any phase interpolators. To this end, a fractional divider controlled by CDR is placed close to the global phase locked loop. Moreover, in order to address the sub-optimal lock point of conventional baud-rate phase detectors, the proposed CDR employs a background eye-climbing algorithm, which optimizes the sampling phase and maximizes the vertical eye margin (VEM). Fabricated in a 28nm CMOS process, the proposed 4x32Gb/s RX shows a low integrated fractional spur of -40.4dBc at a 2500ppm frequency offset. Furthermore, it improves bit-error-rate performance by increasing the VEM by 17%. The entire RX achieves the energy efficiency of 1.8pJ/bit with the aggregate data rate of 128Gb/s.