A Novel Error Separation Technique for Quadrature Modulators and Demodulators

Abstract

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 iii 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 counversion 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.

New estimation and compensation method for quadrature modulator and demodulator errors in digital predistortion system

“…Besides, to design the predistorter, a feedback loop is always necessary in the DPD system, and a portion of the distorted PA output signal is fed back and down-converted by the quadrature demodulator (QDM), which also has in-phase and quadrature (IQ) imbalance errors. The IQ imbalance errors caused by both QM and QDM, which work on the up-conversion and down-conversion circuits, respectively, will degrade the linearization performance of DPD significantly [8][9][10][11][12][13][14]. So it is necessary to compensate for those errors in the DPD system to achieve better linearization performance.…”

Experimental performance evaluation of error estimation and compensation technique for quadrature modulators and demodulators

“…Previously, we proposed the error estimation technique for a QMOD and a QDEMOD by using a variable phase shifter as another solution against the problem described above and evaluated the performance through computer simulation [5]. In this paper, we report the results of the experimental performance evaluation of this technique in the case that the output of a QMOD is directly connected to the input of a QDEMOD.…”