  We present a GlobalFoundries 22FDX FD-SOI application-specific integrated
circuit (ASIC) of a beamspace equalizer for millimeter-wave (mmWave) massive
multiple-input multiple-output (MIMO) systems. The ASIC implements a
recently-proposed power-saving technique called sparsity-adaptive equalization
(SPADE). SPADE exploits the inherent sparsity of mmWave channels in the
beamspace domain to reduce the dynamic power of matrix-vector products by
skipping multiplications for which the magnitude of both operands are below
pre-defined thresholds. Simulations with realistic mmWave channels show that
SPADE incurs less than 0.7dB SNR degradation at 1% target bit error rate
compared to antenna-domain equalization. ASIC measurement results demonstrate
an equalization throughput of 46Gbps and show that SPADE offers up to 38% power
savings compared to antenna-domain equalization. A comparison with
state-of-the-art massive MIMO equalizer designs reveals that our ASIC achieves
superior normalized energy efficiency.
