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A 56 Gbps 2-tap 4-level pulse amplitude modulation closed-loop decision feedback equalizer (DFE) is designed in 28 nm CMOS technology. The first-tap feedback signal directly tapped from the slicer causes uncontrolled overshoot, resulting in over-correction. With insignificant hardware and power consumption, an overshoot compensation scheme is proposed, which generates an opposite overshoot to compensate the original one. Simulation results show the overshoot caused by different process-voltage-temperature conditions during the sampling aperture is reduced by at least 40%. More than 59% improvement is achieved in recovered eye height over its conventional counterpart with ≥ 9 dB channel loss at 14 GHz. In addition, a two-stage slicer is proposed to resolve the critical timing constraints of the first-tap direct feedback path. The receiver occupies an area of 0.19 mm2, and consumes a power of 179 mW, achieving 3.2 pJ/bit energy efficiency. [ABSTRACT FROM AUTHOR]

A novel equal-slope baud rate clock and data recovery (CDR) algorithm is proposed. By positioning the locked point on pulse response where pre-cursor slope and main-cursor slope are equal, an optimized eye-opening is achieved with enhanced eye height, eye width and timing margin. The algorithm is realized in high-speed wireline receiver by finding the sampling position with maximum probability over an adaptive reference voltage when adjacent two data are opposite, with a double transition density over conventional Mueller-Muller (MM) algorithm. With no need for extra power-consuming or timing-critical circuits, this algorithm is readily integrated into prevalent decision feedback equalization (DFE). Simulation shows more than 18.0%, 14.4% and 56.1% improvement in recovered eye height, eye width and time margin, respectively, over its MM counterpart with >10 ​dB channel loss@14 ​GHz. Clear eye improvement could also be seen with respect to classical bang-bang CDR. Moreover, equal-slope CDR demonstrates significant locked point stability against system noise thanks to alienation from nearly-flat region. [ABSTRACT FROM AUTHOR]