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Digital Electronics: Principles, Devices and Applications

Digital Electronics: Principles, Devices and Applications

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88 <strong>Digital</strong> <strong>Electronics</strong>AYBEA00001111B00110011(a)E01010101YZ1Z1Z1Z0Z= High Impedance stateAYBEA00001111B00110011(b)E01010101Y1Z1Z1Z0ZZ= High Impedance stateFigure 4.27Tristate devices.4.8 Schmitt GatesThe logic gates discussed so far have a single-input threshold voltage level. This threshold is thesame for both LOW-to-HIGH <strong>and</strong> HIGH-to-LOW output transitions. This threshold voltage liessomewhere between the highest LOW voltage level <strong>and</strong> the lowest HIGH voltage level guaranteed bythe manufacturer of the device. These logic gates can produce an erratic output when fed with a slow

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