An input sampling stage circuit includes, a precharge buffer, a precharge switch-capacitor circuit, and an input sampling capacitor. The precharge buffer is configured to buffer an input voltage. The precharge switch-capacitor circuit includes a plurality of switches, a first capacitor, and a second capacitor configured such that the first and second capacitors are connected in series during a coarse sampling time and in parallel during a fine sampling time and charge transfer time. The input sampling capacitor is configured to sample the input voltage through the precharge switch-capacitor circuit during the coarse sampling time and sample the input voltage directly during the fine sampling time.