Area-Efficient 28-GHz Four-Element Phased-Array Transceiver Front-End Achieving 25.2% Tx Efficiency at 15.68-dBm Output Power

An area-efficient 28-GHz four-element phased-array transceiver front-end (TRx FE) is proposed in this article. Transmitter/receiver (T/R) switch, phase shifter (PS), and power combining/splitting network all use customized coupler-based structures to replace area-consuming quarter-wavelength ( $\lambda $ /4) transmission line (T-line) structures. In Tx mode, a three-stage power amplifier (PA) is designed by cascading a class-AB predriver amplifier, a deep class-AB driver amplifier, and a class-A output amplifier for high output power. In Rx mode, a two-stage low noise amplifier (LNA) is designed with a 3-bit resistive adjusting load for high dynamic range of input power. A coupler is adopted in the variable gain amplifier (VGA) to achieve constant phase during gain adjustment. The proposed TRx FE is fabricated in a 40-nm CMOS process. Measurement results show that output 1-dB compression point (OP1dB) of 14.99 dBm and saturated output power (OPsat) of 15.68 dBm with 25.2% power efficiency are achieved in each Tx element. In each Rx element, noise figure (NF) of 4.54 dB, input 1-dB compression point (IP1dB) of −10.15 dBm, and maximum gain of 26.3 dB with 56.1-mW power consumption are realized. The gain range of Rx/Tx mode is 9.9–26.3 dB/24.2–44.6 dB with a resolution of 0.3 dB and phase variation less than 2° at 28 GHz. Thanks to the area-efficient coupler-based structures, the phased-array TRx FE occupies an area of 0.42 mm2 for each element and 0.084 mm2 for total area of combiner/splitter, achieving high area efficiency for Ka-band phased-array TRx FEs.