A 15–22 Gbps Serial Link in 28 nm CMOS With Direct DFE

A half-duplex serial link design that is capable of 22 Gbps operation over PCB channels with up to 20 dB of loss is presented. A current-mode transmitter can be configured either as a pre-cursor or post-cursor 2-tap FIR filter. The receiver consists of a trans-admittance-trans-impedance single-stage linear equalizer that can provide 10 dB of high-frequency gain without the use of peaking inductors. The CTLE is followed by an half-rate 2-tap decision feedback equalizer with direct feedback. To mitigate long-tail intersymbol interference in a power-efficient manner, a third DFE tap employs a single-pole IIR filter. A 15-22 GHz LC-PLL provides quadrature clocks to a 16-lane macro. The 16-lane macro occupies 1.66 mm × 1.6 mm in a 28 nm CMOS process and is packaged in a 45 mm × 45 mm flip-chip MCM module. The link operates from two power supplies at 1.35 V and 0.9 V with a BER and a power efficiency of 6.5 mW/Gbps at 20 Gbps.