Class ab amplifier

An amplifier, comprising:

• a first input transistor having a first electrode, a second electrode, and a control terminal for receiving a first input voltage;
• a first impedance unit coupled to the first electrode of the first input transistor;
• a current source coupled to the second electrode of the first input transistor;
• a first push-pull output circuit comprising a first PMOS transistor and a first NMOS transistor electrically connected in series to output a first output voltage, wherein the first electrode of the first input transistor is coupled to a control terminal of the first NMOS transistor;
• and
• a first level shifting unit coupled between the first electrode of the first input transistor and the first push-pull output circuit, for shifting a voltage of the first electrode of the first input transistor and providing a first shifted voltage corresponding to the voltage of the first electrode of the first input transistor to a control terminal of the first PMOS transistor.