Patent ID: 7400698

Claim:
A shift register circuit, comprising: a first shift register unit comprising a first input terminal, a first output terminal, and a first clock input terminal for receiving a first clock signal; a second shift register unit comprising a second output terminal, a second input terminal electrically coupled to the first output terminal, and a second clock input terminal for receiving a second clock signal, the second shift register unit comprising: a first switch element comprising a first control terminal electrically coupled to the first output terminal, a first terminal, and a second terminal; a second switch element comprising a second control terminal electrically coupled to the second terminal of the first switch element, a first terminal for receiving the second clock signal, and a second terminal electrically coupled to the second output terminal; and a pull down unit, electrically coupled between the second switch element and a reference voltage, for pulling down a voltage level of the second output terminal according to a pull down control signal; a third shift register unit comprising a third clock input terminal for receiving the first clock signal, a third input terminal electrically coupled to the second output terminal, and a third output terminal; and a fourth shift register unit comprising a fourth clock input terminal for receiving the second clock signal, a fourth input terminal electrically coupled to the third output terminal, and a fourth output terminal, the fourth shift register unit comprising: a third switch element comprising a third control terminal electrically coupled to the third output terminal, a first terminal, and a second terminal; and a fourth switch element comprising a fourth control terminal electrically coupled to the second terminal of the third switch element and the pull down unit, a first terminal for receiving the second clock signal, and a second terminal electrically coupled to the fourth output terminal, wherein the fourth shift register unit generates the pull down control signal according to a voltage level of a connected node of the third switch element and the fourth switch element.