A direct conversion transmitter with digital-assisted DC offset and I/Q phase calibration

Abstract

A direct conversion transmitter with auto-calibration mechanism is presented in this paper. Both the carrier leakage and in-phase/quadrature (I/Q) phase imbalance are compensated by a proposed calibration algorithm to improve transmitter's single-sideband performance. The digital-assisted correction circuits are implemented in a calibration feedback path to reduce the mismatches and variations, which in turn achieves properties of high linearity, high sideband, and carrier suppression ratio. The measured single-sideband performance with calibration applied to the transmitter demonstrates an over 40 and 50-dBc rejection on sideband and carrier signals at the desired frequency band, respectively. For linearity performance, the measured output 1-dB compression point (OP1dB) is 9.1dBm, while the highest voltage gain is from 4.3 to 6.2dB. Additionally, the error vector magnitude (EVM) of -37.082dB (< 1.4%) can be achieved under an orthogonal frequency division multiple access (OFDMA) 64 QAM-3/4 modulated signal test. The transmitter consumes 112.7mA under supply voltage of 3.3V using the TSMC SiGe BiCMOS technology. Copyright (c) 2017 John Wiley & Sons, Ltd.