Design considerations in high-order multi-bit sigma-delta modulators

A study of dynamics of high-order single-loop multi-bit sigma-delta modulation is presented. The improved stability characteristics of multi-bit modulation result in a wider stable input range than that of one-bit modulation. A quasi-linear relationship is shown to exist between the stable input ranges of two modulators with a difference only in the number of quantization levels. A trade-off between the stable input range and baseband quantization noise suppression in an N-bit modulator allows it to achieve more than 6N dB in signal-to-noise ratio as well as further suppression of discrete tones associated with the limit-cycle effect.