Cascaded ΣΔ ADC with adaptive interstage coupling

A novel architecture for cascaded sigma-delta modulators based on adaptive interstage coupling (AIC) is presented. Most cascaded sigma-delta systems have two interstage coupling coefficients (ICCs), a sub-unity multiplicative factor α and an additive integer factor γ, to constrain the input level of the cascaded stage. Theoretically, γ does not affect the final combined output, while the factor α degrades the SNDR by 20log(α^-1)dB for each cascaded stage. Replacing α by an adaptive γ, the AIC design eliminates the above degradation, increases both the dynamic range and peak SNDR, and relaxes the matching tolerances of the ICC values. The performance of the AIC structure is evaluated and compared to the traditional design for a MASH 2-1 architecture, using behavioral simulations at an oversampling ratio of 16. The results confirm an improvement of 12 dB in the dynamic range and about 10 dB in the peak SNDR