A Predistortion-Less Digital MIMO Transmitter With DTC-Based Quadrature Imbalance Compensation

Abstract

A four-element multi-input multi-output (MIMO) switched capacitor power amplifier (SCPA) in 22-nm fully depleted silicon-on-insulator (FD-SOI) is presented as a softwaredefined radio. To omit the digital predistortion (DPD) and digital quadrature correction power consumption of this wide modulation bandwidth MIMO transmitter, constant-conductance SCPA drivers and a wideband low-impedance power supply are used for linearization. Digital-to-time converter (DTC)-based clock calibration is used for quadrature imbalance correction, improving image rejection to >53 dB. This allows for up to 80-MHz DPD-less single carrier 1024-quadrature amplitude modulation (QAM) transmission, with an error vector magnitude (EVM) <−39.4 dB. RF bandwidths up to 160 MHz are demonstrated for multicarrier 1024 QAM signals, supporting data rates up to 1.18 GBps. A second-order Chebyshev bandpass filter using bondwires as inductors is used as a matching network, supporting carrier frequencies from 1.64 to 3.28 GHz, while omitting the required chip area for integrated inductors. MIMO experiments demonstrate the beamforming capabilities for single and multibeam communication.Index Terms-CMOS integrated circuits, digital beamforming, digital-to-time converter (DTC), radio frequency digital-to-analog converter (RF-DAC), switched capacitor power amplifier (SCPA).