Abstract: An operational amplifier providing an output voltage signal to drive a load in response to an input voltage signal is provided. The operational amplifier includes a first input stage and a second input stage, a second stage and an output enable switch. The first input stage provides a first intermediate signal according to the voltages of an input and an output voltage signals in a transitional state. The second input stage provides a second intermediate signal according to the input and the output voltage signals in a steady state. The second stage provides the output voltage signal to an output node according to the first and the second intermediate signals in the transitional and the steady states respectively. The output enable switch is enabled in an output enable period to drive the load with the output voltage signal.