A Novel Calibration Method of DC-Offsets in Direct-Conversion Transmitter

Abstract

Direct-conversion transmitter based on the zero intermediate frequency architecture has been widely used. However, the direct current offsets (DC-offsets) introduced by the modulator affect the system performance and severely limit the calibration of IQ imbalance errors. This letter focuses on estimating and calibrating DC-offsets of modulators in the transmitter. Based on the frequency difference between the transmitted local oscillator (LO) signal and the received LO signal, the parameters of DC-offsets can be estimated by exploiting a training sequence and a self-closed loop system to achieve digital pre-compensation. The frequency response of the feedback loop and the interference introduced by the receiving channel can be ignored. There is no need to add additional hardware circuits, and the algorithm’s complexity is lower than other methods. In addition, the frequency-independent IQ imbalance errors in the transmit channel are accurately estimated. Finally, the effectiveness of the proposed algorithm is verified by simulation.