A Low-Power High-Speed Dynamic Comparator With a Transconductance-Enhanced Latching Stage

Abstract

Low-power, high-speed dynamic comparators are highly desirable in the design of high-speed analog-to-digital converters (ADC) and digital I/O circuits. Most dynamic comparators use a pair of cross-coupled inverters as the latching stage, which provides strong positive feedback, to accelerate the comparison and reduce the static power consumption. The delay of the comparator is mainly determined by the total effective transconductance of the latching stage. The delay not only limits the maximum operating frequency but also extends the period of the metastable state of the latching stage; hence, it increases energy consumption. However, at the beginning of the comparison phase, the conventional latching stage has two transistors with zero gate-to-source voltage, which degrade the total effective transconductance of the latching stage. In this paper, a novel low-power, high-speed dynamic comparator with a new latching stage is presented. The proposed latching stage uses separated gate-biasing cross-coupled transistors instead of the conventional cross-coupled inverter structure. The simple proposed latching stage improves its effective total transconductance at the beginning of the comparison phase, which leads to a much faster comparison and lowers energy consumption. The comparator is analyzed and compared to its prior type in terms of delay and power consumption via simulations and measurements. The experimental results demonstrate that the proposed comparator operates from a 1.2-V supply and consumes 110-fJ energy per comparison, with sampling speeds up to 2 GS/s.