Mismatch cancellation in quadrature bandpass ΔΣ modulators using an error shaping technique

Abstract

A technique for shaping component mismatch error in the real and imaginary paths of a complex (quadrature) /spl Delta//spl Sigma/ are studied and simulated. Complex bandpass /spl Delta//spl Sigma/ modulators provide improved performance over a pair of real bandpass /spl Delta//spl Sigma/ modulators of the same order in the conversion of narrow-band quadrature intermediate frequency (IF) signals. This is possible due to elimination of redundant conjugate pairs of poles and zeros in its noise and signal transfer function. Mismatches in the modulators real and imaginary paths, however, results in spectral leakage of image band interference and image band quantization noise to the passband of the converted output. Strategic pole-zero placement, as well as adaptive techniques has been studied in earlier works. The work presented here takes advantage of the inherent dual paths of the complex bandpass /spl Delta//spl Sigma/ modulator to reduce component mismatch effects using a switched capacitor error shaping technique.