A 140 GHz 4-Channel High Power Density Beamforming Front-End in 40-nm Bulk CMOS

This paper presents a 4-channel RF beamforming front-end in 40-nm CMOS. Each channel integrates an active phase shifter, a variable-gain amplifier, and a power amplifier. Quadrature signals are generated by on-chip Lange coupler, and the phase is set by a digitally controlled PS. The VGA adopts a differential common-source topology with current-steering gain control. The PA employs a 2-way on-chip power combiner. Each unit PA is a three-stage differential common-source amplifier with cross-coupled capacitive neutralization. On-wafer measurements show 16.1 dB peak S21 and 10.3 GHz 3-dB bandwidth. At 140 GHz, the per-channel P1dB and PSAT are 6 dBm and 11.5 dBm, respectively. The RMS phase and amplitude errors are 1.6° and 0.2 dB, respectively. The core area is 0.76 mm2. To the best of our knowledge, this work achieves the highest power density among D-band RF beamformers while maintaining low RMS phase and amplitude errors across the operating band.