A Phase-Modulation Phase-Shifting Phased-Array Transmitter With Phase Self-Calibration and Deep PBOs Efficiency Enhancement

In this article, a digital phase-modulation (PM) phase-shifting (PS) phased-array transmitter is proposed. Both PM and PS are implemented in a PS modulator. Meanwhile, a self-calibration loop is introduced in the PS modulator for improved phase linearity and minimized phase error. The phase control voltages for the PS modulator are generated from the self-calibration loop based on the output signals and reference signals. To reduce the calibration time, a capacitor-array-based state store memory is introduced in the self-calibration loop. Efficiency at 2.5-/6-/12-dB power back-off (PBO) is enhanced by class-G Doherty switched-capacitor power amplifier (SCPA). As a verification of the concept, a 2.1-2.9-GHz four-element phased-array transmitter is designed and fabricated in a conventional 40-nm CMOS technology. The transmitter features a 10-bit fast-locking phase self-calibration with measured 0.4 degrees rms phase error and 0.2-dB rms power error. The measured peak saturated output power of each element is 26.95 dBm at 2.4 GHz. Besides, the measured system efficiency at 0-/2.5-/6-/12-dB PBO is 37.25%/34.24%/30.12%/21.23%. For 20-MHz 64-QAM/15-MHz 256-QAM modulation signal, it exhibits EVM of 4.65%/2.84%, average output power of 19.91/16.59 dBm, and average system efficiency of 24.12%/19.21% at 2.4 GHz. By connecting monopole antenna units with a gain of 4.21 dBi, the measured peak effective isotropic radiated power (EIRP) of phased-array transmitter is 42.05 dBm.