An input buffer is configurable for use as a standard buffer with a single switching threshold, selectable to be one of at least two different switching thresholds, or used as a Schmitt trigger circuit with hysteresis, which uses at least two switching thresholds from among the at least two different switching thresholds. The integrated circuit may be a programmable logic device (PLD) or field programmable gate array (FPGA), but in other embodiments, the integrated circuit may be other types of devices such a microprocessors, ASICs, or memories.