Influence of LFSR Dither on the Periods of a MASH Digital Delta–Sigma Modulator

This brief shows that applying a linear feedback shift register (LFSR) dither to a digital delta-sigma modulator (DDSM) cannot always increase its fundamental period. For some DDSMs, the LFSR dither may reduce its period in some cases, instead of increasing it, which worsens the output spectrum. Hence, this brief calculates the dithered DDSM's period and analyzes the influence of LFSR dither on the period. Furthermore, for this kind of DDSM, this brief explains how to add the LFSR dither to increase the period for a full input range. Finally, the experiment is performed to confirm the analysis.