An improved successive-approximation type ADC that uses both charge-scaled and voltage scaled approximation. The present invention provides a high noise immunity, high speed ADC using a differential voltage scaled DAC. The differential voltage scaled output scheme of the present invention advantageously applies voltage scaling to a capacitor on both inputs to the comparator. The dual voltage scaling is preferably done by connecting two switches to each tap on the bottom half of a resistor string, and no switches to the top half of the resistor string, using one set of tap switches for adjusting a charge on capacitor on the first input of the comparator and the second set of tap switches for adjusting a charge on capacitor on the second input of the comparator.