| 摘要 |
For use in a semiconductor circuit device, a uniquely-arranged tri-state output buffer responds to a control signal generated in the semiconductor circuit device and a below-ground voltage level at an output terminal to prevent wasted drain current and substrate current, and reduce capacitance at the pull-up node driving the output terminal. The output buffer includes a power supply signal providing at least one voltage level with respect to common; an output terminal; a pull-up node; a pull-down node; a first circuit responding to the control signal by providing a first control voltage on the pull-up node; and a second circuit responding to the control signal by providing a second control voltage on the pull-down node. Further, the output buffer includes a pull-up transistor, responsive to the voltage on the pull-up node and coupled between the power supply signal and the output terminal; a pull-down transistor, responsive to the voltage on the pull-down node and coupled between common and the output terminal; a bias circuit, responsive to a voltage level on the output terminal being at a level substantially below common, arranged to bias the pull-up node downwardly and away from the voltage level provided by the power supply signal; and a disable circuit, responsive to the voltage level on the output terminal being at a level substantially below common, constructed and arranged to disable the circuit providing the control voltage on the pull-up node. The pull-up transistor provides a high-level signal at the output terminal, the pull-down transistor provides a low-level signal at the output terminal, and the bias circuit in combination with the disable circuit respond to the voltage level on the output terminal being at a level substantially below common by preventing current flow from the power supply signal to the output terminal.
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