This work reports an 8-lane single-ended RX featuring compact and low power far-end crosstalk (FEXT) cancellation circuits. The RX data-path consists of a cross continuous-time linear equalizer (XCTLE) to remove FEXT by nearest aggressors within the channel bundle. Residual post-cursor FEXT is suppressed by a direct feedback 7x8-tap cross decisionfeedback equalizer (XDFE). A CTLE and 8-tap DFE equalize single-ended channels with 28dB insertion loss at Nyquist frequency without TX FFE. The circuit, fabricated in 32nm SOI CMOS, was measured to receive 7Gb/s/pin PRBS11 data at BER < 10 −12 with 12.5%UI margin. It occupies 300x350µm 2 with an energy efficiency of 5.9mW/Gb/s. Introduction Over the past decade, aggregate I/O bandwidth requirements have increased at a rate of approximately 2x-to-3x every 2 years [1]. Single-ended-signaling improves aggregate datarate, resulting in nearly twice the performance of similar buses operating with two differential lines per signal. Unfortunately, single-ended PCB traces with reduced lane-to-lane spacing suffer from increased crosstalk (xtalk) noise by electromagnetic coupling. A significant challenge is to ensure proper signal transmission over single-ended wires at rates previously attainable only with differential pairs. In this work, a powerful equalization method is proposed that combines a cross continuous-time linear equalizer (XCTLE) and multi-tap cross decision-feedback equalizer (XDFE). Since far-end crosstalk (FEXT) is approximately proportional to the derivative of the channel, FEXT(ω)=-jωβH(ω) [2] a XCTLE equalizes xtalk by differentiating the received signals from nearest neighbors and adding them with appropriate gain (G0,G1) to match the xtalk strength β as proposed in [2]. Compared to [2], the implemented RX does not require wider spacing between bundle pairs, since residual error terms are suppressed by the XDFE. Furthermore, a XDFE compensates non trivial xtalk patterns generated by connectors and via-arrays. Only the synergy between XCTLE and XDFE results in error free data for the channel investigated in this work. Although RX with multi XDFE taps are commonly used in ADC-based 100/10GBASE-T transceivers, they are not yet used for chip-to-chip link owing to their increased demand for power and area. A low power analog 56-tap XDFE is implemented using a switched capacitor (SC) approach proposed in [3].Architecture Fig.1 shows the architecture of our RX circuit which is intended for use in source-synchronous links. It consists of 8 single-ended data lanes and 1 shared differential clock lane. The reference voltage V ref is extracted from the differential clock common-mode using a low-pass filter. The received signal is terminated to V dd =1V (1V, 500mV DC levels at RXin) using T-coils for bandwidth enhancement in the product-level ESD protection circuit. The signals on the victim and adjacent aggressor lanes are processed by a XCTLE, which uses two single-ended high-pass RC filters to differentiate the aggressor signals. The xtalk cancellation and fo...
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