Diode-based IQ imbalance estimation in direct conversion transmitters

Direct conversion transmitters are widely used in wireless systems for their inherent features of being simple and low cost. In this architecture, the inphase (I branch) and quadrature signal (Q branch) will be unconverted to the RF frequency band by quadrature modulation. However, the drawback of the direct conversion architecture is that it is sensitive to IQ imbalance caused by the impairment of analogue devices in I and Q branches. It then results in interferences in mirror frequencies which degrades the signal quality. Therefore, the accurate measurement of IQ imbalance is crucial. A diode-based method to measure the broadband IQ imbalance is proposed which does not need additional measurement instruments. Measurement results show the effectiveness of this method.