Sampling circuits

The invention provides a sampling circuit, which is operated in the sampling stage and the holding stage. The sampling circuit comprises an amplifier, a first capacitor, a second capacitor and a voltage source. The amplifier has a first input end and an output end for outputting an output signal; the first capacitor is coupled to the first input and is used for sampling the input signal during the sampling stage; the second capacitor has a first end which is coupled to the first input end and a second end which is coupled to the output end during the holding stage and is decoupled with the output end during the sampling stage, the second capacitor is used for sampling a reference signal during the sampling stage and receiving electric amounts from the first capacitor during the holding stage; the voltage source is coupled between the first input end and the output end and is used for providing a presetting voltage level during the sampling stage to remove the difference between an input common-mode voltage an