  Spatial signal processors (SSP) for emerging millimeter-wave wireless
networks are critically dependent on link discovery. To avoid loss in
communication, mobile devices need to locate narrow directional beams with
millisecond latency. In this work, we demonstrate a true-time-delay (TTD) array
with digitally reconfigurable delay elements enabling both fast beam-training
at the receiver with wideband data communications. In beam-training mode, large
delay-bandwidth products are implemented to accelerate beam training using
frequency-dependent probing beams. In data communications mode, precise beam
alignment is achieved to mitigate spatial effects during beam-forming for
wideband signals. The 4-element switched-capacitor based time-interleaved array
uses a compact closed-loop integrator for signal combining with the delay
compensation implemented in the clock domain to achieve high precision and
large delay range. Prototyped in TSMC 65nm CMOS, the TTD SSP successfully
demonstrates unique frequency-to-angle mapping with 3.8ns maximum delay and
800MHz bandwidth in the beam-training mode. In the data communications mode,
nearly 12dB uniform beamforming gain is achieved from 80MHz to 800MHz. The TTD
SSP consumes 29mW at 1V supply achieving 122MB/s with 16-QAM at 9.8% EVM.
