Rail-to-rail operational amplifier

The invention discloses a rail-to-rail operational amplifier which comprises an operational amplification input stage, a buck stage and an output stage, wherein the operational amplification input stage comprises a PMOS (P-channel Metal Oxide Semiconductor) input stage and an NMOS (N-channel metal oxide semiconductor) input stage; and the operational amplification input stage also comprises a mirror image input stage, wherein the mirror image input stage, the PMOS input stage and the NMOS input stage are input in parallel. On the premise that the circuit complexity is not obviously increased, the rail-to-rail operational amplifier can be applied to the 1.8V even lower power voltage conditions, the power consumption of the circuit is greatly lowered, and the design requirement of low voltage and low energy consumption can be satisfied.