A Fully Integrated 27.5-30.5 GHz 8-Element Phased-Array Transmit Front-end Module in 65 nm CMOS

A fully integrated 27.5-30.5 GHz 8-element phased-array transmit front-end module in 65 nm CMOS is presented. The module is based on the all-RF phased-array architecture and consists of 8 phased-array elements. One 1:8 power splitter divides the input power into 8 elements after the driver stages. Each element consists of one 5-bit digital attenuator, one 5-bit phase shifter, one extra 0/180° switching amplifier, one power amplifier and some buffer stages between the above stages to compensate the gain loss. A 5-bit digital attenuator with amplitude and phase calibration is presented to provide 15.5 dB attenuation coverage with 0.5 dB step. A 180° reflection-type phase shifter, along with an 0/180° switching amplifier is proposed to realize 360° phase shifting coverage with 5.625° step. Amplifiers, including power amplifier, 0/180° switching amplifier and buffer stages, adopt wideband inter-stage matching technique to ensure 27.5-30.5 GHz bandwidth coverage. All of the features are digitally controllable. The measurements show that the module achieves <; -10 dB input return loss, about 36 dB gain across 27.5-30.5 GHz and delivers about 12.71 dBm output-referred 1-dB compression point (OP1dB) power at 29 GHz. The module achieves 2.61° RMS (root mean square) phase error with 1.26 dB RMS gain variation across 27.5-30.5 GHz from the phase shifter and 0/180° switching amplifier. The attenuator achieves 0.26 dB RMS amplitude error with 2.79° RMS phase variation. The chip occupies 6.95 × 3.17 mm² area and consumes 1.66 A from the 1.2 V power supplies.