Significantly reduce the information content of a

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Significantly reduce the information content of a signal Have relatively high reliability and noise immunity 9 Achieved by appropriately selecting discrete voltage values Define valid voltage levels Volts Valid logic 0 Valid logic 1 Forbidden X 0 0.5 2.8 3.3 Voltages and digital values Buffer in out In out 0 0 1 1 in out Inverter In out 0 1 1 0 Noise 10 V out V in V in V out = Digital world A 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 11 output than at the input NM L NM H V OL X V IL V IH V OH “0” output “1” output “0” input “1” input Voltages and digital values Noise < V OL “0” > V IH “1” < V IL “0” > V OH “1” < V IL “0” > V OH “1” > V IH “1” < V OL “0” 12 Required Expected Noise margins: NM L =V IL -V OL NM H =V OH -V IH
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