A Three-Stage Comparator and Its Modified Version With Fast Speed and Low Kickback

This brief presents a three-stage comparator and its modified version to improve the speed and reduce the kickback noise. Compared to the traditional two-stage comparators, the three-stage comparator in this work has an extra amplification stage, which enlarges the voltage gain and increases the speed. Unlike the traditional two-stage structure that uses pMOS input pair in the regeneration stage, the three-stage comparator makes it possible to use nMOS input pairs in both the regeneration stage and the amplification stage, further increasing the speed. Furthermore, in the proposed modified version of three-stage comparator, a CMOS input pair is adopted at the amplification stage. This greatly reduces the kickback noise by canceling out the nMOS kickback through the pMOS kickback. It also adds an extra signal path in the regeneration stage, which helps increase the speed further. For easy comparison, both the conventional two-stage and the proposed three-stage comparators are implemented in the same 130-nm CMOS process. Measured results show that the modified version of three-stage comparator improves the speed by 32%, and decreases the kickback noise by ten times. This improvement is not at the cost of increased input referred offset or noise.