Improved Offline Calibration of DAC Mismatch Errors in Delta–Sigma Data Converters

Element mismatch in the digital-to-analog converter (DAC) of a multibit ΔΣ data-converter greatly degrades the modulator's in-band performance. One approach to correct these errors is to use an offline calibration method, based on measuring the output of the modulator in response to an in-band sinusoid. The drawback of this method, however, is the necessity for a distortion-free input sine-wave excitation. We propose a technique that dispenses with the need for a distortion-free input, thereby paving the way for the generation of the input tone on-chip. Apart from being a useful tool for debugging designs, it is a potential candidate for foreground calibration. Experimental results from a multibit modulator test chip, designed in a 180nm CMOS technology, are given.