Operational amplifier and electronic system

An operational amplifier, comprising at least two stages of amplification circuit units, including an output-stage amplification circuit unit and a preceding-stage amplification circuit unit at an upstream of the output-stage amplification circuit unit, wherein the output-stage amplification circuit unit comprises a pair of amplification circuits, each of which comprises a first transistor, a second transistor, a first capacitor and a first DC bias circuit, wherein

• a control electrode of the first transistor is connected with a corresponding output terminal of the preceding-stage amplification circuit unit, a first electrode of the first transistor is connected with a first power terminal, and a second electrode of the first transistor is connected with an output terminal of the amplification circuit comprising the first transistor;
• an output terminal of the first DC bias circuit is connected with a control electrode of the second transistor, to provide a DC bias voltage to the control electrode of the second transistor;
• a first electrode of the second transistor is connected with a second power terminal, and a second electrode of the second transistor is connected with the output terminal of the amplification circuit;
• two ends of the first capacitor are respectively connected with the control electrode of the first transistor and the control electrode of the second transistor so that the first capacitor connects the output terminal of the preceding-stage amplification circuit unit and the control electrode of the second transistor;
• and
• the first transistor and the second transistor are of opposite polarities,
• wherein the first DC bias circuit comprises a first current source and a third transistor, wherein a control electrode and a first electrode of the third transistor are both connected with the control electrode of the second transistor, a second electrode of the third transistor is connected with the second power terminal, an output terminal of the first current source is connected with the first electrode of the third transistor, and the third transistor and the second transistor are of the same polarity.