A novel adaptive mismatch cancellation system for quadrature IF radio receivers

This paper investigates and resolves in-phase/quadrature phase (I/Q) imbala nces between the input paths of quadrature IF receivers, These mismatches a long the paths result in the image interference aliasing into the desired s ignal band, thus reducing the dynamic range and degrading the performance o f the receivers. I/Q errors occur because of gain and phase imbalances betw een quadrature mixers. They are also caused by capacitor mismatches in anal og-to-digital converters (A/D's), which are designed to be identical for ea ch input path, This paper presents a novel and feasible digital signal proc essing (DSP) solution for the I/Q mismatch problems. The system includes a no,el complete least mean square algorithm and a modified adaptive noise ca nceler (signal separator) to separate the desired signal and the image nois e caused by the mismatch. The noise canceler can also solve the signal leak age problem, which is that the noise reference includes signal components. This system was implemented in a Xilinx FPGA and an Analog Devices DSP chip . It was tested with a complex intermediate frequency receiver, which inclu des an analog front end and a complex sigma-delta modulator. Both simulatio n results and test results show a dramatic attenuation of the image noise. Extending applications of the system to N-path systems further indicates th e robustness and feasibility of this novel adaptive mismatch cancellation s ystem.