Importance

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Abstract

A tri-state output buffer circuit employs N-channel pull-up and pull-down transistors, with another N-channel transistor connected between the pull-up and pull-down transistors and having its gate connected to the low-voltage supply. An output node at one side of the pull-up transistor may be driven to a voltage higher than the supply, without subjecting the pull-up to hot-carrier effects or other deleterious effects of over-voltage. When in the high-impedance output state, the gate of the pull-up is shorted to an intermediate node which is the drain of the pull-down transistor, using a P-channel and an N-channel transistor responsive to the logic input. The voltage on the gate of the pull-up transistor is allowed to track the output up to the reduced voltage supply minus V.sub.TN when in the high-impedance state, by tying the gate of the pull-up transistor to the intermediate node; this prevents damage to the pull-up due to hot-carrier effects.

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First Claim