A 6-GHz MU-MIMO Eight-Element Direct Digital Beamforming TX Utilizing FIR H-Bridge DAC

Targeting the next generation of Wi-Fi (WiFi-6E), this work extends the bandwidth and frequency range of digital-phase-shifting direct-digital-to-RF TX, paving the way for use in high-speed multiuser, multiple-input-multiple-output (MU-MIMO) wireless systems. Careful frequency planning and a mostly digital upconversion scheme facilitate digital automation. Digital delta-sigma modulation enables an inherently linear 1b RF DAC. Low-loss digital filtering suppresses delta-sigma DAC noise and mitigates the challenges of filtering a 6-GHz RF frequency. An H-bridge combines current-DAC, finite-impulse response (FIR) filtering, and RF upconversion. A 28-nm CMOS eight-element 6-GHz beamforming TX prototype has a per-element area of 0.01 mm
²
and a per-element power consumption of 47.5 mW.