A Real Time FPGA-based IQ Imbalance Measurement and Calibration System for High Volume Production Testing

Direct conversion receivers have been widely employed in many wireless communication systems by virtue of their simplicity, high selectivity and high performance. Quadrature modulators in these receivers convert an RF input to a baseband in-phase (I) and quadrature (Q) output pair. Any imbalance between I and Q paths would result or rate (BER) and degraded system reliability. This work proposes a new IQ imbalance detection system implemented on an FPGA-based digitizer. The detection system derives the Image Reject Ratio (IMRR) by performing a complex Fast Fourier Transform (FFT) on an IQ baseband input pair, and then subtracting the main tone from the image tone. The proposed system aims to accurately compute the 10 imbalance in direct conversions receivers in real-time, significantly reducing the amount of time needed in automated testing setups. In addition, this system enables FPGA-based digitizers to effortlessly and automatically monitor IQ imbalance, thereby eliminating the need for additional hardware.