Operational amplifier and sampling and amplifying circuit

The invention relates to an operational amplifier and a sampling and amplifying circuit, and the operational amplifier comprises a first-stage circuit which is used for obtaining a first output signal according to a first input signal and a common-mode feedback signal, and generating a first bias signal and a second bias signal when the first output signal is output to a split capacitor; the second-stage circuit is used for generating a third bias signal and a fourth bias signal according to the first bias signal and the second bias signal; and the third-stage circuit is used for obtaining a second output signal according to the third bias signal and the fourth bias signal, and the common-mode feedback signal is obtained according to the second output signal. According to the operational amplifier disclosed by the invention, high speed and high gain can be ensured, and meanwhile, the operational amplifier is manufactured by adopting an advanced process and has relatively high robustness, so that the applicati