A 0.69-Noise-Efficiency-Factor 55× -Preamp-Gain Dynamic Comparator With a Stacking FIA

This article presents a fully dynamic, low-noise, low-power comparator. Its key highlight is the four-times current-reuse factor, which improves the pre-amplifier gain by at least two times without increasing the power consumption. This causes the proposed design to have a two-times smaller input-referred noise and a two-times better noise-efficiency factor (energy $\times $ noise power). In prior comparators, the maximum current-reuse factor of the pre-amplifier was only two times. This small current-reuse factor limits the pre-amplifier gain to 30 times, which restricts the further improvement in the noise-efficiency factor. By contrast, this work stacks two floating inverter amplifiers (FIAs) in order to greatly increase the current-reuse factor to as large as four times. As a result, the pre-amplifier gain is increased by 55 times, which is helpful for improving the noise-efficiency factor. Implemented in a 28 nm CMOS process, the prototype comparator achieves a $38~{\mu }$ V input-referred noise and a 0.48 pJ energy consumption per comparison under a 0.9 V supply. The noise-efficiency factor is as good as 0.69 nJ $\cdot \mu $ V2, which is three times better than the prior FIA-based comparator and 23 times better than the classic StrongArm latch (SA latch). This noise-efficiency factor is the best among all reported works so far.