On-line calibration and digital correction of multi-bit sigma-delta modulators

This paper presents a new method for the on-line calibration of the elements of the digital-to-analog converter (DAC) used in the feedback loop of multi-bit sigma-delta (ΣΔ) modulators. The proposed method, with an extremely limited amount of additional circuitry, allows the mismatches among the elements of the DAC to be accurately measured and corrected in the digital domain, thus improving the linearity performance of the modulator. A switched-capacitor (SC) 4-bit ΣΔ modulator has been implemented to validate the proposed solution. The experimental results confirm that this method allows us to achieve an improvement in the spurious-free dynamic range as large as 26 dB.