A 2.29pJ/b 112Gb/s Wireline Transceiver with RX 4-Tap FFE for Medium-Reach Applications in 28nm CMOS

Abstract

The increasing demand for higher network data rates by new businesses and entertainment has never been fulfilled. Mixed-signal PAM - 4 transceivers prevail over their ADC - DSP counterparts in energy efficiency and chip area, but they have difficulties operating over high - loss links. Typically, a continuous-time linear equalizer (CTLE) and a multi-tap decision-feedback equalizer (DFE) are implemented in a mixed-signal receiver (RX). However, when the data rate reaches 112Gb/s, the implementation of the DFE suffers from stringent feedback timing. Direct DFE works only at 100Gb/s in an optical receiver [1], leaving no room for feedforward error correction (FEC). A speculative 1 - tap DFE is implemented in [2], but it requires an 8-tap feedforward equalizer (FFE) at the transmitter (TX) to generate a 1+0.5D response; this may be impractical without knowing the characteristics of the entire channel. Another drawback of a speculative DFE is the large 1st-tap latency, which brings about challenges in realizing two or more taps. In addition, the DFE does not compensate for pre-cursor inter-symbol interference (ISI), which becomes significant for channels with higher loss. Without a DFE, the CTLE only covers a small loss of up to 10dB [3,4]. This paper presents a 112Gb/s mixed-signal transceiver using an RX analog FFE with adaptive pre- and post-cursor ISI equalization in 28nm CMOS, compensating for 20.8dB loss at a power efficiency of 2.29pJ/b.