Design of a Delta-Sigma Modulator structured in MASH 2-1-2 with dither of error feedback

This paper presents a novel Delta Sigma Modulator (DSM) in form of MASH 2-1-2, which can suppress the spurious tones in spectrum for all constant inputs with error feedback as dither. As a finite-state machine (FSM), DSM always outputs a periodic sequence (or cycle) with a constant input. However, the novel DSM was designed to break up the periodic cycles and suppress quantization noise occurred in the fractional-N frequency synthesizer. Starting from the linear model of DSM, the principle of noise shaping was analyzed and logic implementation is introduced in detail. The performance is confirmed mathematically, by simulation, and experimental results.