Patent ID: 8446182

Claim:
An output buffer applied in a semiconductor device for outputting a data signal according to an enable signal and input data, comprising: a first output transistor, comprising a first terminal coupled to a first operational voltage and a second terminal for outputting the first operational voltage as the data signal; a first switch, comprising: a first terminal coupled to a bulk of the first output transistor; and a control terminal receiving the enable signal; a second switch, comprising: a first terminal coupled to a second terminal of the first switch; a control terminal receiving the enable signal; and a second terminal coupled to a second operational voltage; and a third switch, comprising: a first terminal coupled to the bulk of the first output transistor; a control terminal coupled to the second terminal of the first switch; and a second terminal coupled to the first operational voltage, wherein when the enable signal has a first level, the first switch is turned off and the second switch is turned on to pass the second operational voltage to turn on the third switch so that the bulk of the first output transistor has a bulk voltage equal to the first operational voltage, wherein when the enable signal has a second level and a high voltage larger than the first operational voltage is applied to the second terminal of the first output transistor to lift up the bulk voltage toward the high voltage, the second switch is turned off and the first switch is turned on to pass the bulk voltage to turn off the third switch.