Spatial filtering in flash A/D converters

Averaging networks suppress the random mismatch between the comparators in flash A/D converters (ADCs), but an analytical understanding does not exist, nor a method for optimal design. This paper unifies various forms of offset averaging and derives the optimum by treating the averaging network as a spatial filter. At the optimum, the offsets in terms of LSB are minimized with almost no loss in comparator unity-gain bandwidth. This work leads to an easy-to-follow procedure to design efficient and fast CMOS flash-type ADCs.