Ultra Broadband Phased-Array Transmitter with Low Phase Error of 1.24-2.8° across 36-91 GHz Supporting 10.8 Gbps 64QAM in 90 nm SiGe

Joint sensing and communication utilizing the large bandwidths and spectral bands distributed across $30-100 \mathrm{GHz}$ provide new opportunities for 6G networks for more optimal spectrum and resource utilization, and environmental awareness. However, adaptive operation and spectral agility needed in such a universal array interface capable of operating across all the licensed/unlicensed/shared bands $(30-100 \mathrm{GHz})$ for intelligent communication and sensing is extremely challenging. In this paper, we focus on an element of this array, particularly the ultrawideband phased array transmitter (Tx) element that maintains extremely low maximum phase error below 0.5 LSB, r.m.s. phase error $\approx 0.25$ LSB $\left(1.24-2.8^{\circ}\right)$, and r.m.s. gain error of $0.24-0.35$ dB with a 5-bit phase control across $36-91 \mathrm{GHz}$. The Tx also demonstrates 30-35 dB gain with $10 \mathrm{~dB}$ gain control, $O P_{1 d B}$ of $9-13.5 \mathrm{dBm}$, and a Tx chain efficiency of $10.9 \%$ at $O P_{1 d B}$ at 60GHz. The architecture employs 1) broadband commonbase PA with deep learning enabled matching for bandwidth enhancement; 2) vector summing phase shifter with 90° hybridbased bandwidth extension network for ultra-wideband differential quadrature signal generation and phase control; and 3) multi-stage differential VGA with a tailored frequency response. At 60GHz, it supports $10.8 \mathrm{~Gb} / \mathrm{s}$ 64-QAM signal with $-25.6 \mathrm{~dB} /-$ 31.9dBc EVM/ACLR. To the best of the authors’ knowledge, this is the first Tx beamformer that covers from 5G FR2 to W band with a fractional bandwidth of $87 \%$.