Analysis and Performance Comparison of a Cascade 3-1 Delta-Sigma Topology

In this paper a cascade 3-1 feedforward ¿¿ topology is introduced and compared with other fourth order ¿¿ ADC´s. The third order first loop reduces problems with quantization noise leakage from classical 2-1-1 or 2-2 cascade topologies, leading to lower OTA specifications. Compared to a fourth order single loop converter, more aggressive noise shaping is possible, leading to a lower OSR for the same SNR. By comparing the required OSR and OTA specifications for different fourth order structures, the optimal topology can be chosen depending on the ratio Pdig/Pan. The cascade 3-1 topology is the most favorable choice when this ratio lies between 0.37 and 1.06.