Novel loop architectures for enhancing linearity and resolution of analog-to-digital converters

This paper proposes three mixed (analog and digital) loop architectures which involve an analog-to-digital converter and enhance its linearity and its resolution. Their benefits are discussed with mathematical models and high-level simulations (the ADC inserted in the loops is then a passive sigma-delta structure). One of the loop topologies is particularly highlighted: it is ideally able to enhance resolution by 5 bits without damaging bandwidth. The only added analog element is an active differential low-pass filter. The other operators are fully digital: a predictor and some models of the analog parts. The effect of some defaults, such as mismatch and common mode, is illustrated by high-level simulations. The needed accuracy for the digital parameters is evaluated to 16 bits. The test of a prototype realized in a 0.358m CMOS technology validates the principle and demonstrates that the critical element of the structure is the active differential filter