| 摘要 |
The present invention provides an improved input/output (I/O) circuit that comprises a pair of buffers, a voltage reference circuit that provides first and second reference voltages to the buffers respectively, and a detection circuit. The detection circuit detects whether a supply voltage is below a switching voltage, which is a pre-selected value between operating ranges of two pre-defined supply voltages, e.g., 3.3V and 5V, respectively. If the supply voltage is below the switching voltage, the detection circuit controls the voltage reference circuit to set the first and second reference voltages to first and second predetermined values, e.g., a ground level and the supply voltage, respectively. In this way, the large signal swings of the signals output by the buffers can be substantially maintained. Therefore, high speed operations can be achieved.
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