An effective implementation of high-order bandpass sigma-delta modulators for high speed D/A applications

This paper presents a multiplier-free structure for implementing high-order bandpass digital sigma-delta modulators. Near-optimum noise suppression in the passband region of the modulator is achieved by constraining the Noise Transfer Function (NTF) zeros to lie on the unit circle, even after coefficient quantization. High-speed operation is obtained by using a highly modular structure with minimum critical path delays which are independent of the modulator order. Results from various simulations and experimental prototypes are given to illustrate both the stability of the designs and the flexibility of the overall structure.