| 摘要 |
The present invention is an ESD protection circuit that discharges both positive and negative electrostatic events. A preferred embodiment of the circuit comprises a first NMOS transistor having a source and drain connected between ground and an I/O pad and second and third NMOS transistors and a resistor connected in series between ground and the I/O pad. The gate and body of the first transistor and the bodies of the second and third transistors are connected to a node between the second and third transistors; the gate of the second transistor is connected to the I/O pad through a second resistor; and the gate of the third transistor is connected to ground. The second and third transistors maintain the gate and body voltage of the first transistor at the pad voltage when the pad experiences negative voltages and at ground voltage when the pad experiences positive voltages. As a result, the first transistor can discharge both negative and positive ESC events through parasitic bipolar conduction, without any additional circuits such as diodes used either to stop leakage currents or to conduct ESD current.
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