An investigation of bandpass sigma-delta A/D converters

This paper presents an investigation of the performance characteristics of a pair of bandpass Sigma-Delta (/spl Sigma/-/spl Delta/) analog-to-digital (A/D) converters. One of these /spl Sigma/-/spl Delta/ A/D converters has the conventional cascade-of-integrators structure while the other has the conventional cascade-of-resonators structure. These /spl Sigma/-/spl Delta/ A/D converters are subsequently compared in terms of their achievable signal-to-quantization noise ratios for corresponding (discrete) switched-capacitor implementations. Based on this comparison, a new bandpass /spl Sigma/-/spl Delta/ A/D converter structure is proposed which possesses the best practical features of both converters. These include, complementary signal and noise transfer functions and the fact that the zeros of the noise transfer function are constrained to lie on the unit-circle.