A 0.061-pJ/b/dB 28-Gb/s Gradient-Based Maximum Eye Tracking CDR With 2-Tap DFE Adaptation in 28-nm CMOS

Abstract

This brief presents a gradient-based maximum eye tracking (GMET) scheme employed in the forwarded-clock receiver, including baud-rate clock and data recovery (CDR) and 2-tap adaptive decision feedback equalization (DFE). By optimizing the widely used gradient ascent method for robust operation, GMET achieves low computational power and high stability. Also, simultaneous adaptation using the unified algorithm enables low power consumption and low design complexity. Compared with the previous baud-rate CDR, superior performance is demonstrated under high-loss conditions. The prototype receiver is fabricated in 28-nm CMOS and occupies an active area of 0.106 mm2. At the data rate of 28 Gb/s, the receiver consumes 47 mW, corresponding to an energy efficiency of 1.68 pJ/b. Furthermore, with a channel loss of 27.7 dB at the Nyquist frequency, joint operation of the CDR and the DFE adaptation offers measured results with a margin of 0.17 unit interval (UI) at a BER lower than 10-12.