Fully Digital Transmit Equalizer With Dynamic Impedance Modulation Ranko Sredojević, Student Member , IEEE, and Vladimir Stojanovi ć,M e m b e r ,IEEE

Abstract

This paper analyzes the energy ef ficiency of different transmit equalizer driver topol ogies. Dynamic impedance mod- ulation is found to be the most energy-ef ficient mechanism for transmit pre-emphasis, when c ompared with impedance-main- taining current and voltage-mode drivers. The equalizing transmitter is implemented as a digital push–pull impedance-modulating (RM) driver with fully digital RAM-DAC back-end for pattern lookup. Thi s back-end compensates for both duty-cycle distortion and drive r nonlinearity, while providing a programmable pre-emphasis. A testchip fabricated in 90-nm CMOS process shows relatively small signal degradation from dynamic modulation of driver output impedance over a variety of 20 backplanes at 4 Gb/s, with energy ef ficiency of 2 pJ/bit at 100 mV of receiver eye. Despite this signal degradation, at the same performance point, the impedance modulating driver shows better energy ef ficiency than impedance-ma intaining current and voltage-mode drivers.