A 1.2-GHz comparator with adaptable offset in 0.35-[micro]m CMOS

We apply the technique of floating-gate differential injection to a 1.2-GHz CMOS comparator to achieve arbitrary, accurate, and adaptable offsets. The comparator uses nonvolatile charge storage on floating-gate nodes for either offset nulling or automatic programming of a desired offset. We utilize impact-ionized pFET hot-electron injection to achieve fully automatic offset programming. The design has been fabricated in a commercially available 4-metal, 2-poly 0.35-[micro]m CMOS process. Experimental results confirm the ability to reduce the variance of comparator offset by 3600 x and to accurately programa desired offset with maximum observed residual offset of 469 [micro]V and standard deviation of 199 [micro]V. We achieve controlled injection to accurately program the input offset to voltages uniformly distributed from--1 to 1 V. The comparator operates at 1.2 GHz with a power consumption of 3.3 mW. Index Terms--Adaptive systems, analog-digital conversion, analog memories, calibration, CMOS analog integrated circuits (ICs), comparators, floating gate, high-speed ICs, hot carriers, offset cancellation.