A new method of improving speed of latch-type comparators with preamplifier is presented. It investigates the relationship of current and transistor scales which affect delay time(tp) in latch. It applies a mathematical model to optimize latch design. A figure of merit indicates that ratio Ipmos/Inmos is 0.25 in latch leading to optimal delay time. In order to suppress offset of latch, the cross-coupled loading, adopted in telescope preamplifier, which enhances the gain, is well analyzed and designed. The chip is fabricated in 0.18 μm CMOS technology. The delay time of latch comparator is less than 400 ps @500 MHz. The offset of comparator is estimated through Monte Carlo simulation. And power consumption is only 144 W under 1.8 V power supply. Results of on wafer testing are presented at the end of the paper. The chip occupies an area of 0.66×0.55 mm^2 and drains current of 80 μA.
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