Ultra-Broadband I/Q RF-DAC Transmitters

Abstract

An ultra-broadband I/Q RF-DAC digital wireless transmitter architecture is proposed for 5G terminals and base stations. Broadband 1–32-GHz and tuned 20–32-GHz $2 \times 6$ -bit versions of the transmitter were designed and manufactured in a production 45-nm SOI CMOS technology. They feature a process-and-temperature invariant quadrature phase generator with less than 1.4° phase error from 1 to 32 GHz, and a series-stacked, gate-segmented $2 \times 6$ -bit I/Q RF-DAC. The transistor-level schematics of each block, and novel series-differential inductors for broadband common-mode rejection and differential-mode bandwidth extension are described in detail. The tuned transmitter prototype with transformer-coupled output stage achieved 19.9-dBm output power with record data rates of up to 30 Gbit/s and 24.6-pJ/bit efficiency in the 20–32-GHz range using QPSK, 16-QAM, 32-QAM, and 64-QAM modulation formats. The measured output power of the broadband transmitter is 18.4 dBm and remains larger than 13 dBm from 1 to 32 GHz. On-die generation of 16-QAM, 32-QAM, and 64-QAM modulated carriers at data rates of up to 20, 15, and 6 Gbit/s, respectively, was demonstrated.