An impact of introducing multi-level signals to a bandpass cascaded delta-sigma modulator

The impact of introducing multi-level signals to a bandpass delta-sigma modulator (DSM), which is of particular interest for wireless communications applications, has been investigated. A cascaded architecture is studied, since this is favorable to obtain high resolution as well as stability. By increasing the number of the signal levels from two to 16, we have improved the DSM signal-to-noise ratio by 24 dB, or by 4 bits. This amount of improvement is almost the same as that for conventional lowpass DSMs. Our simulation also indicated that, if a mismatch in intervals between levels was introduced in the DSMs, the noise-shaping characteristics were modified considerably, and the signal-to-noise ratio (SNR) decreases. The dynamic element matching technique, in particular the mismatch-shaping scheme, was proved effective to improve the SNR, even if the mismatch exists.