A new design for cascaded sigma-delta modulators

A new architecture of cascaded sigma-delta modulators is presented. It is based on the combination of two algorithms, the Adaptive Integrator Bounding (AIB) and the Adaptive Interstage Coupling (AIC). The AIB concentrates on constraining the signal ranges within each stage, while the AIC eliminates the SNR degradation caused by the coupling coefficients between stages. Although each of the two algorithms was developed individually and hence functions independently, combining them makes both more effective and efficient. Simulation results show that the more cascaded stages, the more improvement this new design will provide. Compared to available designs, it improves the peak SNRs by about 10 dB, 14 dB, 29 dB and 37 dB respectively for the cascaded 2-1, 2-2, 2-2-1 and 2-2-2 systems at an oversampling ratio of 24. In addition, the implementation of the AIC algorithm is simplified when the AIB is adopted in the previous stage