A differential difference comparator for multi-step A/D converters

The proposed Differential Difference Comparator (DDC) provides easy linear voltage summing/subtraction and comparison functions via current operation. The speed of this unconventional comparator drastically improved since there is no feedback loop and coupling capacitors needed to maintain the linearity. The linear input range is also enlarged by the common mode compression. The principle, design considerations and simulation results are presented based on a comparator used in an 8 bit 2-step A/D converter over 100 MS/s.