A circuit that includes an input stage circuit and an output stage circuit is provided. The input stage circuit includes a differential pair circuit and two output current mirror circuits. The differential pair circuit operates according to a first voltage source to receive a first and a second input voltages and generate a first and a second output currents. The two output current mirror circuits operate according to a second voltage source to generate a first current mirror output current fed to an input stage output node according to the first output current and generate a second current mirror output current flowed from the input stage output node according to the second output current. The output stage circuit operates according to the second voltage source to receive an input voltage from the input stage output node to generate an output voltage.