A sampling circuit includes an amplifier, a sampling capacitor, a feedback capacitor, and a voltage source. The sampling capacitor and the feedback capacitor are coupled to the same input terminal of the amplifier, such that the offset of the amplifier and low-frequency noise can be cancelled. The voltage source can shift the voltage level of an output signal of the sampling circuit by the difference between the input and output common mode voltages of the amplifier, so that an amplifier having different input common mode voltage and output common mode voltage can be adopted, and the capacitance of the sampling capacitor and that of the feedback capacitor can be different, resulting in a non-unit gain.