Mismatch cancellation for double-sampling sigma-delta modulators

The performance of double-sampling sigma-delta A/Ds can suffer due to capacitor mismatch as well as uneven clock phases. Improving the resulting SNR is essential. This paper presents a method that uses DSP techniques to filter out the mismatch. Simulation results of applying an adaptive LMS filter to a fourth-order double-sampling bandpass sigma delta modulator are presented that show an improvement in SNR of more than 30 dB.