10 Gb/s adaptive receive-side merged near-end and far-end crosstalk cancellation circuitry in 65 nm CMOS

Abstract

Crosstalk between neighboring channels can have significant impact on system bit-error rate (BER) as serial I/O data rates scale above 10 Gb/s. This paper presents receive-side circuitry which merges the cancellation of both near-end and far-end crosstalk (NEXT/FEXT) and can automatically adapt to different channel environments and variations in process, voltage, and temperature. NEXT cancellation is realized with a novel 3-tap FIR filter which combines two traditional FIR filter taps and a continuous-time band-pass filter IIR tap for efficient crosstalk cancellation, with all filter tap coefficients automatically determined via an on-die sign---sign least-mean-square (SS-LMS) adaptation engine. FEXT cancellation is realized by coupling the aggressor signal through a differentiator circuit whose gain is automatically adjusted with a power-detection-based adaptation loop. A prototype fabricated in a general purpose 65-nm CMOS process includes the adaptive NEXT and FEXT circuitry, along with a continuous-time linear equalizer (CTLE) to compensate for frequency-dependent channel loss. Enabling the crosstalk cancellation circuitry while operating at 10 Gb/s over coupled 4-in FR4 transmission line channels with NEXT and FEXT aggressors opens a previously closed eye and allows for a 0.2 UI timing margin at a BER = 10ź9. Total power including the NEXT/FEXT crosstalk cancellation circuitry, CTLE, and high-speed output buffer is 34.6 mW, and the core circuit area occupies 0.3 mm2.