This paper deals with quadrature demodulators used for Zero Intermediate Frequency (ZIF) and Near Zero Intermediate frequency (NZIF) receivers. ZIF and NZIF receivers are more sensitive to circuitry mismatch, which causes I-Q imbalance. With IQ-Balancing (IQB) technology, any adverse effect of frequency-dependent I-Q imbalance can be removed and quadrature receivers can have high tolerance to the I-Q imbalance. The paper first provides detailed description of the IQB technology for a simple I-Q network. Then the paper shows that any I-Q operations (ideal or non-ideal) can be described by an I-Q network and that the I-Q network can be described by a set of 2-by-2 matrixes, each of which defines the imbalance condition at a given frequency. As a result, the IQB technology can be applied to the I-Q network to remove any adverse effect. The paper then explains how the IQB technology can be used with a quadrature demodulator for ZIF/NZIF receivers for any modulation schemes. Finally, two application examples are included to show how the proposed quadrature demodulator can make ZIF/NZIF receivers have much higher tolerance to I-Q imbalance. System simulation results are provided for a ZIF receiver for OFDM signals and a NZIF receiver for GMSK signals.
Jian Gu, Jian Gu,
"Zero-IF and near-zero-IF quadrature demodulators with high tolerance to I-Q imbalance", Proc. SPIE 4911, Wireless and Mobile Communications II, (22 August 2002); doi: 10.1117/12.480535; https://doi.org/10.1117/12.480535