Adaptive Digital Signal Processing Algorithms for Image-Rejection Mixer Self-Calibration

By Gabriel M. Desjardins

Abstract:

This report details Digital Signal Processing (DSP) methods for optimizing the performance of a self-calibrating image-rejection mixer, as well as a custom VLSI implementation of one such algorithm. The mixer is part of a Double-Conversion Wide-Band IF receiver designed to support the Digital European Cordless Telephone (DECT) and the Global System for Mobile Communications (GSM) Standards, which have carrier frequencies of 1.9 GHz. Different numerical methods were evaluated according to computational complexity, convergence time and convergence accuracy. We developed a variable step-size adaptive algorithm to remove inherent mismatches in the mixer circuit. Various DSP architectures were also simulated with the minimization of circuit area and power consumption in mind. Simulation showed that the optimization process arrived at a phase mismatch of 0.0129 degrees and a gain mismatch of 0.0114% for an ADC output noise level of -76 dBV, as specified in the receiver frequency plan. This allows us to achieve a mean image-rejection ratio of 78 dB across a wide frequency range irrespective of variations with operating temperature. The mean convergence time of the algorithm is 590 μs. The DSP system occupies less than 0.08 mm2 of chip area in a 0.25 μm CMOS process and has a pre-layout power consumption of 13 μW for a 1.0V supply.

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