A Novel Error Separation Technique for Quadrature Modulators and Demodulators

In recent mobile communication systems, impairments in analog circuits cannot be disregarded due to achieving high performance. Errors in analog circuits consist of a distortion of a power amplifier(PA), gain and phase imbalance in a quadrature modulator (QMOD) and a quadrature demodulator (QDEMOD), dc offset, frequency offset, and so on. Because of high accuracy of compensation, many techniques of error compensation by using a digital signal processing have been studied recently. Digital predistorter (DPD), which can eliminate odd-order distortion caused by PA nonlinearity, is one of the compensation techniques, but in the case that direct conversion architecture is used in a loop-back path, errors in QMOD and QDEMOD affect the performance of DPD. In this paper, we propose a novel technique for error separation for QMOD and QDEMOD error estimation by adding a phase shifter to the conventional DPD architecture