Patent ID: 7859807

Claim:
An electrostatic discharge (ESD) protection circuit for protecting an output circuit, comprising: a loading element coupled between an output terminal of the output circuit and a first node carrying a first operating voltage; a first plurality of diodes connected in series and forming a diode string and coupled between the output terminal and the first node; a first clamping circuit coupled between the first node and a second node carrying a second operating voltage; a second clamping circuit, one terminal of the second clamping circuit coupled to the second node, and the other terminal of the second clamping circuit coupled to a first connecting node of a closest diode and a second closest diode to the output terminal among the diode string; and a third clamping circuit, one terminal of the third clamping circuit coupled to the second node, and the other terminal of the third clamping circuit coupled to a second connecting node between two adjacent diodes in the diode string other than the two adjacent diodes that connect to form the first connecting node, wherein a number of the diodes in the diode string is greater than or equal to three; wherein a number of the diodes in the diode string is greater than or equal to a voltage swing of the output terminal divided by a turn-on voltage of one of the diodes.