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Significantly reduce the information content of a signalHave relatively high reliability and noise immunity9Achieved by appropriately selecting discrete voltage valuesDefine valid voltage levelsVoltsValid logic 0Valid logic 1Forbidden X0 0.5 2.8 3.3Voltages and digital valuesBufferinoutIn out0 01 1inoutInverterIn out0 11 0Noise10VoutVinVinVout=Digital worldA voltage represents a valid “0”, a valid “1” or an invalid signal “X”To make sure that “0” is not mistaken for “1” we apply stricter boundaries to the signal values at the 11output than at the inputNMLNMHVOLXVILVIHVOH“0” output“1” output“0” input“1” inputVoltages and digital valuesNoise< VOL “0”> VIH “1”< VIL “0”> VOH “1”< VIL “0”> VOH “1”> VIH “1”< VOL “0”12Required ExpectedNoise margins: NML=VIL-VOLNMH=VOH-VIH
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