DAC mismatch shaping in Discrete Time Sigma Delta ADCs with non uniform quantizer

Discrete time ΣΔ modulators habitually use a multi-level uniform quantizer (UQ); with this type of quantizer the maximum resolution is reached around full scale and system stability is improved. In this work, we propose the use of a multi-level non uniform quantizer (NUQ) to improve resolution for low input amplitude signals. The proposed architecture is compared with a uniform quantizer, and the effect of feedback DAC mismatch is analyzed. Different DAC mismatch shaping techniques are tested to compare their effects on SNR and SFDR, focusing on rotational element selection and Bi-DWA. Simulations are performed with MATLAB using behavioral modeled blocks. Results indicate that DAC mismatch produces a noticeable SNR degradation in converters with non uniform quantizer; DAC mismatch shaping methods are compared, rotational element selection being better in terms of SNR and Bi-DWA is better in terms of SFDR.