Non-Invasive Quadrature Modulator Balancing Method to Optimize Image Band Rejection

The design, simulation, and implementation of a non-ideal quadrature modulator balancing system based on the image rejection using correction factors with non-invasive and simple method is given. The novel balancing system proposed in this paper improves the performance of the quadrature modulator by eliminating the imperfections inherent in the RF systems. Furthermore, the proposed system improves DC offsets that can exist at the output of digital-to-analog converters in addition to frequency-dependent loss and phase shift of low-pass anti-aliasing filters by optimizing the image band rejection. The complete analytical model for a non-ideal quadrature modulator is developed and verified for several conditions. The method is non-invasive and requires only two sets of measurements to obtain the correction factors for amplitude and phase of I and Q signals. The proposed method eliminates the requirement for existing time consuming pre-calibration methods where the system is measured before operation and correction factors that depend on several parameters are stored in memory to be recalled during operation.