A 4-Element Digital Modulated Polar Phased-Array Transmitter with Phase Modulation Phase-Shifting

Abstract

A novel architecture of a digital modulated polar phased-array transmitter with phase modulation (PM) phase-shifting and feed-forward controlled dynamic matching (FFCDM) is presented in this article. Phase-shifting in a PM signal path is utilized in each element, which shares many components including a phase modulator, baseband, and IF components. The characteristics of the proposed architecture are analyzed. With a constant envelope of PM signals, the implicit nonlinearity of the phase shifter in this architecture has low impact on the linearity performance of a phased-array system. Meanwhile, low phase error can be achieved by high-resolution phase interpolation with the digital predistortion (DPD) technique. Efficiency for both saturated and 6-dB back-off power is enhanced by digital power amplifier (DPA) with FFCDM. As a proof of concept, a 3-7 GHz 4-element phased-array transmitter is designed and fabricated in 40-nm CMOS based on the proposed method. The measured root-mean-square (rms) phase error of 0.3°, effective phase shifting resolution of 9-bit, and peak system efficiency of 38.2% are achieved. For 40 MHz 64-QAM modulation signal, it exhibits EVM of 5.38% and 5.37%, $P_{\text {out}}$ of 14.30 and 14.46 dBm, and PAPR of 7.08 and 6.97 at 3.5 and 5.2 GHz, respectively. The measured peak EIRP is 35.6 dBm with a unit antenna gain of 2.98 dBi at 5 GHz. The radiation patterns with 0°, 15°, 30°, and 45° steering are measured based on monopole antennas. Meanwhile, the array achieves < 4.7% and < 5.9% EVM for 64-QAM signals with bandwidths of 20 and 40 MHz, respectively.