Multi-Mode Spatial Signal Processor With Rainbow-Like Fast Beam Training and Wideband Communications Using True-Time-Delay Arrays

Initial access in millimeter-wave (mmW) wireless is critical toward successful realization of the fifth-generation (5G) wireless networks and beyond. Limited bandwidth in existing standards and use of phase-shifters in analog/hybrid phased-antenna arrays (PAAs) are not suited for these emerging standards demanding low-latency direction finding. This work proposes a reconfigurable true-time-delay (TTD)-based spatial signal processor (SSP) with frequency-division beam training methodology and wideband beam-squint less data communications. Discrete-time delay compensated clocking technique is used to support 800-MHz bandwidth with a large unity-gain bandwidth ring-amplifier (RAMP)-based signal combiner. To extensively characterize the proposed SSP across different SSP modes and frequency–angle pairs, an automated testbed is developed using computer vision techniques that significantly speeds up the testing progress and minimizes possible human errors. Using seven levels of time-interleaving for each of the four antenna elements, TTD SSP has a delay range of 3.8 ns over 800 MHz and achieves unique frequency-to-angle mapping in the beam training mode with nearly 12-dB frequency-independent gain in the beamforming mode. The SSP is prototyped in 65-nm CMOS with an area of 1.98 mm2 consuming only 29 mW excluding buffers. Furthermore, an error vector magnitude (EVM) of 7.3% is realized for 16-QAM modulation at a speed of 614.4 Mb/s.