On reduced-order filter design for uncertain cascaded 2-1 sigma-delta modulators

In this paper, we present a new robust matching filter design method for uncertain 2-1 cascaded sigma-delta modulators. This method addresses a well known limitation of H-infinity loop shaping techniques that they yield filters of high order (equal to the sum of the plant order and the order of the weighting function), thus increasing the complexity of circuit implementation. In contrast, the new method yields filters whose order is equal to the plant order, independent of the weighting function. We compare the new method with other existing fixed-order designs, and establish its efficacy.