Delta-sigma modulator with switching loop filter based on the linear gain

The article proposes a technique of using the modern control theory for the design of the loop filter. A delta-sigma modulator is an analog-to-digital (A-D) converter. The proposed technique has achieved a high SNR with stability. On the other hand, other researchers have proposed, focusing on the structure of a delta-sigma modulator, multistage noise-shaping (MASH), which involves two interleaved single integration loops. Furthermore, a method of switching a stable loop filter for high input amplitude and a high-SNR loop filter for low input amplitude was proposed. The 5th-order loop filter with the oversampling ratio of 32 was designed. The difference in the loop filters between the high-SNR mode and the stable mode was in the value of the Lee criterion option of the synthesize NTF function. Generally, when the value of the Lee criterion is increased, high SNR is provided.