Analysis and Design of a Low-Voltage Low-Power Double-Tail Comparator

The need for ultra low-power, area efficient, and high speed analog-to-digital converters is pushing toward the use of dynamic regenerative comparators to maximize speed and power efficiency. In this paper, an analysis on the delay of the dynamic comparators will be presented and analytical expressions are derived. From the analytical expressions, designers can obtain an intuition about the main contributors to the comparator delay and fully explore the tradeoffs in dynamic comparator design. Based on the presented analysis, a new dynamic comparator is proposed, where the circuit of a conventional double-tail comparator is modified for low-power and fast operation even in small supply voltages. Without complicating the design and by adding few transistors, the positive feedback during the regeneration is strengthened, which results in remarkably reduced delay time. Post-layout simulation results in a 0.18-mu m CMOS technology confirm the analysis results. It is shown that in the proposed dynamic comparator both the power consumption and delay time are significantly reduced. The maximum clock frequency of the proposed comparator can be increased to 2.5 and 1.1 GHz at supply voltages of 1.2 and 0.6 V, while consuming 1.4 mW and 153 mu W, respectively. The standard deviation of the input-referred offset is 7.8 mV at 1.2 V supply.