A Chain-Weaver Balanced Power Amplifier With an Embedded Impedance/Power Sensor

Abstract

This article introduces an N-way chain-weaver balanced power amplifier (PA) for millimeter-wave (mm-wave) phased-array transmitters (TXs). Taking advantage of the proposed combining network, an embedded impedance/power sensor is implemented, which can be utilized for output power regulation, built-in self-test, and load-based performance optimization. The proposed PA architecture offers linearity and gain robustness under the antenna's frequency/time-dependent voltage standing wave ratio (VSWR). In the event of impedance mismatch, the proposed PA provides N different loads equally distributed on the VSWR circle. Consequently, the performance of the PAs is the average of N PAs with N different loads, which makes this structure VSWR resilient. As a proof of concept, an eight-way chain-weaver balanced PA (BPA) is realized in 40-nm bulk CMOS technology, and it delivers 25.19-dBm P
_SAT with 16.19% PAE. The proposed PA supports a 2-GHz 64-QAM OFDM signal with 16-dBm average power, achieving -25-dB error vector magnitude (EVM). The average EVM is better than -30.3 dB without digital pre-distortion (DPD) for an "800-MHz 256-QAM OFDM"signal while generating an average output power of 12.17 dBm. The performance of the PA is also evaluated under 1.5:1-3:1 VSWR conditions. The measured small-signal gain variation under VSWR 3:1 is ±0.7 dB. Moreover, assuming any frequency/time-dependent loading condition within the VSWR 3:1 circle, the proposed chain-weaver BPA achieves <2.8° amplitude-to-phase (AM-PM) over 3-GHz bandwidth. Besides, the embedded impedance/power sensor accuracy outperforms the state of the art. The proposed impedance sensor can measure VSWR 3:1 by the maximum angle and magnitude errors of 12.3° and 0.106, respectively.