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

Summary 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 9.1 dBm, while the highest voltage gain is from 4.3 to 6.2 dB. Additionally, the error vector magnitude (EVM) of −37.082 dB (< 1.4%) can be achieved under an orthogonal frequency division multiple access (OFDMA) 64 QAM‐3/4 modulated signal test. The transmitter consumes 112.7 mA under supply voltage of 3.3 V using the TSMC SiGe BiCMOS technology. Copyright © 2017 John Wiley & Sons, Ltd. The novelty of this paper is to investigate an improvement of the linearity and sideband suppression ratio with proposed digital‐assisted calibration circuits. The measured single‐sideband performance with calibration applied to the transmitter demonstrates an over 40 and 50‐dBc rejection on sideband and carrier signals, respectively. Additionally, for linearity performance, the error vector magnitude (EVM) of −37.082 dB (< 1.4%) is achieved under an orthogonal frequency division multiple access (OFDMA) 64 QAM‐3/4 modulated signal test.