Digital link pre-emphasis with dynamic driver impedance modulation

Digital push-pull impedance-modulating (RM) pre-emphasis driver overcomes the power overhead of equalization in voltage-mode (VM) drivers, improving the output stage efficiency ∼2–3x. A compact, fully-digital RAM-DAC implementation with pattern lookup compensates both duty-cycle distortion and driver nonlinearity, while providing a programmable pre-emphasis. A testchip fabricated in 90nm CMOS process shows relatively small signal degradation from dynamic modulation of driver output impedance over a variety of 20″ backplanes at 4Gb/s, with energy-efficiency of 2pJ/bit at 100mV of receiver eye.