Study of fully digital error correction in multibit delta-sigma A/D converters

In this paper, fully digital error correction for delta-sigma analog-to-digital converters is studied with emphasis of feedback DAC error reshaping. In correction of the converter output, the estimated DAC error must be reshaped according to converter´s input-output transfer function. By examples, we demonstrate how a non-unity DAC noise transfer function complicates the signal processing as there might be a need for additional digital filtering in the correction. This arises in typical multiple-feedback type topology because the DAC error transfer function is the signal transfer function (STF) without distributive input signal branches, making it inherently lowpass-type. Advantage of feedforward type delta-sigma topology arises as its STF is inherently wideband so a need for additional filtering in digital error correction can be completely avoided. This property is studied with emphasis of basic off-line error correction scheme