A comparison system including a dynamic comparator, a background offset calibration circuit, and an asynchronous reset timing control circuit is presented. The background offset calibration circuit is coupled to the dynamic comparator, and generates calibration signals in response to reference switching control signals. Where calibration signals are used to calibrate the input refer offset of the dynamic comparator. The asynchronous reset timing control circuit is coupled to the dynamic comparator and the background offset calibration circuit, and generates a control clock signal and the reference switching control signals in response to the output signals of the dynamic comparator and a plurality of basic clock signals. During each clock cycle of the first basic clock signal, the control clock signal is used to control the dynamic comparator to perform two data comparison, one for the input refer offset and the other for a differential input signal.