Low delay dispersion comparator for level-crossing ADCs

This paper presents a comparator with low delay dispersion for level-crossing analog-to-digital conversion applications. The comparator comprises a technique to compensate the delay dispersion caused by variable input overdrive. The whole circuit is composed of three main blocks, namely, conventional comparator, fixed delay block and variable delay block. The variable delay block is controlled such that it implements the inverse overdrive-delay characteristics of the conventional comparator. Therefore, the overall delay dispersion of the circuit is effectively reduced. Using the proposed technique in a level-crossing ADC would enable the sampling of a signal with 6.15X higher frequency than the case of using a conventional comparator keeping the same SNR. The circuit is implemented in 65nm technology. The active area of the circuit is 267.8μm² and the measured power consumption is 273μW at 200MHz.