A 16-Element Fully Integrated 28GHz Digital Beamformer with In-Package 4×4 Patch Antenna Array and 64 Continuous-Time Band-Pass Delta-Sigma Sub-ADCs

This paper presents a fully-integrated 28GHz mm-wave digital beamformer, combined with a custom-designed 8-layer LTCC substrate 4×4 patch antenna array, for a complete 16-element single-chip mm-wave-to-digital beamforming system. 16-element digital beamforming in a single IC represents an excellent tradeoff between die size, signal loss, and I/O routing complexity. Optimum placement of the ADCs, together with the use of four 27GHz PLLs, shortens both LO and mm-wave signal routing and reduces signal loss. ADC sampling of a high (1GHz) IF enables single-phase mm-wave LO routing and moves the I/Q mixing into the digital domain. A 4× parallel band-pass ADC structure provides in-built FIR filtering for additional harmonic suppression and anti-alias filtering. Bit-stream processing takes advantage of the short bit-width outputs of the RX slices to implement digital beamforming with area and energy-efficient MUXes. The prototype 16-element beamformer generates four independent, simultaneous beams. Over-the-air measurements confirm accurate 3D beam patterns, indicate a measured overall noise figure of 7dB, and QAM-4 EVM of -18dB.