Automatic within-pair-skew compensation for 6.25Gbps differential links using wide-bandwidth delay units

This paper presents an automatic on-chip skew compensation scheme for within-pair-skew (WPS) in differential high-speed links. The skew compensation is achieved by cascading a series of wide-bandwidth delay cells to obtain constant group delay over the signal bandwidth. A continuous-time correlation circuit with current-mode logic XOR gate followed by a RC low-pass filter is proposed for skew detection. The effects of WPS and the proposed skew compensation scheme have been studied for various time skew and channel attenuation values. Simulation results show that the proposed skew compensation circuits can successfully restore the signal quality close to the condition without WPS, even when the signal with WPS has completely closed eyes. © 2006 IEEE.