POLES AND ZEROS OF BANDPASS-FILTERS FOR HIGH-PERFORMANCE SIGMA-DELTA MODULATORS

High-performance bandpass sigma-delta modulators find applications in digital mobile radio for accurate analogue-to-digital conversion in re ceivers. An approach based on the positioning of the poles and zeros i s proposed for the digital design of the high-order loop filters which are required, Inverse notch filter sections are cascaded in a first s tep and then poles and zeros are moved to meet the performance objecti ves and achieve system stability. A distinct feature of the analysis a nd design technique presented is that it takes stability into account explicitly. Examples illustrate the practicality of the method as well as the level of performance which can be achieved in theory. The inte grated circuit realization still has to be investigated to confirm the potential of the proposed design approach.