A DAC-Based Discrete Multitone Wireline Transmitter in 5nm FinFET

Abstract

As process nodes shrink, DSP and DAC-based transmitters (TX) are increasingly attractive for ultra high-speed long-reach wireline systems. Discrete multitone modulation (DMT) is a promising candidate for high-speed links due to its ability to overcome impedance discontinuities with high spectral efficiency, using area-efficient feedforward frequency-domain equalization. This work presents a DMT TX, implemented in a 5nm FinFET process, targeting a 112 Gb/s data rate. The TX DSP includes per-sub-channel bit and power loading so that each frequency-domain sub-channel can optimize its symbol modulation order and power to the sub-channel SNDR. The 31 sub-channels can be individually loaded given the channel SNDR profile to minimize the bit error rate. The transmitter incorporates a 16-way, 7-bit high-speed DAC and a DMT DSP. The chip has been fabricated but is pending silicon testing. Preliminary validation before chip tapeout was performed using an RFSoC platform, and these results are presented in the ISSCC SRP.