This comparator is used in the sar adc, uh?The switches and the capacitors uesd here are to sample the input signal and cancell the offset of the comparator and compare the input signal and ref signal. The switch timings need non-overlap. The vaule of the capacitor mainly depends on noise requirments of the sar adc. For further resarch, you can refer to chapter swithed capacitor of Razavi's book.