Design optimisation procedure for digital mismatch compensation in latch comparators

Digital calibration schemes generally allow for high-speed operation and reduced power consumption at the price of lower accuracy compared with their analogue counterparts. However, in dynamic comparators, when exceeding 4 or 5 bits, any resolution increase will be progressively traded against the circuit parameters. This study presents a three-step design procedure to optimise the comparator performance for a given N. First, a new configuration of the latch comparator has allowed optimising the comparison speed in terms of N. Second, the calibration scheme has been reduced to a simple digital sequencer to perform a progressive capacitive offset trimming. Third, the sequencer automatic increment has been programmed to stop at optimal operation to achieve the best calibration accuracy. The proposed method has then been applied to design a latch comparator with 7 bit calibration control in a commercially available 0.18 μm complementary metal-oxide-semiconductor technology. Post-layout statistical simulations have shown that the circuit can achieve up to 5.9 bit calibration resolution without altering the comparator performances.