An auto-calibrating companion bit successive approximation system uses sampling and balancing capacitors in a charge redistribution digital-to-analog converter having multi-valued capacitors of magnitudes enabling redundant expression of electric charge values. Companion bits are used with sets of balancing capacitors for successive approximation of sampling voltages. A charge redistribution digital-to-analog converter has a sampling and balancing capacitors including associated companion bit capacitors represented by digital weights which are saved in memory. A non-binary weighted set of capacitors provides redundancy in a charge redistribution digital-to-analog converter employed in a successive approximation register architecture.