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

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 software defined 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.