Digital-domain calibration of multistep analog-to-digital converters

A digital-domain self-calibration technique, which can directly measure and cancel code errors in multistep conversions, is developed to improve the linearity of multi-step analog-to-digital converters (ADCs). While conventional self-calibration techniques require separate digital-to-analog converters (DACs) for calibration purpose to subtract nonlinearity errors in the analog domain, the proposed digital calibration technique uses add-on digital logic to subtract nonlinearity errors digitally from uncalibrated digital outputs. In a prototype 12-b fully differential two-step ADC implemented using a 2-μm n-well CMOS technology, this technique cancels MOS switch feedthrough, op-amp offsets, and interstage gain errors simultaneously, and improves total harmonic distortion from -64 to -77 dB