Patent ID: 6326832
Filing Date: 2001-12-04
Classification: H03K

Abstract:
An apparatus comprising:an output device formed at least partially in a well of a semiconductor workpiece, the output device including an input node and an output node;a power supply rail configured to output a power supply voltage to the well; andan isolation circuit positioned between the well and the power supply, the isolation circuit permitting electrical communication between the power supply and the well only when a voltage on the output node of the output device is smaller than the power supply voltage; andwherein the output device includes an output inverter comprising:a pull-up output transistor formed in the well, the pull-up output transistor having a control node in electrical communication with the input node of the output device, an input node in electrical communication with the power supply rail, and an output node in electrical communication with the output node of the output device; anda pull-down output transistor formed outside of the well, the pull-down transistor having a control node in electrical communication with the input node of the output device, an input node in electrical communication with a low power rail, and an output node in electrical communication with the output node of the output device; andwherein the isolation circuit comprises:a switching inverter including,a pull-up switching transistor having a control node in electrical communication with the power supply rail, an input node in electrical communication with the output node of the output device, anda pull-down switching transistor having a control node in electrical communication with the power supply rail, and an input node in electrical communication with the low power rail; andan isolation transistor including,a control node in electrical communication with an output node of the pull-up switching transistor and an output node of the pull-down switching transistor,an input node in electrical communication with the power supply rail, andan output node in electrical communication with the well,whereby application of an output voltage exceeding the power supply voltage to the output node of the output device causes the switching inverter to apply a control voltage to the control node of the isolation transistor, thereby deactivating the isolation transistor and isolating the well from the power supply rail.