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from Ch 23 Logic Gates-2 - Making sense of EE 2nd edition...

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© 2008 A. Ganago How Can We Implement Logic Operations in Circuits? The diode and transistor circuits, which we already studied, can perform logic operations In the following circuits, we assume the positive logic that is “0” = LOW 0 V and “1” = HIGH 5 V Transistors will be in cutoff mode (open circuit) or saturation mode (short circuit) © 2008 A. Ganago This Transistor Circuit Acts As An Inverter C E B R C V CC = 5 V R B Input Signal Output Signal Consider the input signal, which is either 0 V (open circuit CE ) or 5 V (short circuit CE ) © 2008 A. Ganago BJT Inverter (1) C R C R E V CC = 5 V Output Signal 5 V open E I C = 0 I B = 0 B Input signal 0 V When the input is LOW, the output is HIGH © 2008 A. Ganago BJT Inverter (2) C R C V CC = 5 V Output Signal 0 V Input signal 5 V When the input is HIGH, the output is LOW V CE = 0 B I B © 2008 A. Ganago Diode AND Circuit 5 V Output Signal Input signals A B C If both inputs are HIGH the diodes don’t conduct and the output is HIGH If any of the inputs is LOW, the output is LOW This is AND © 2008 A. Ganago BJT NOR Circuit 5 V Output Signal Input signals A B If both inputs are LOW the BJTs don’t conduct and the output is HIGH If any of the inputs is HIGH, the output is LOW This is NOR Making sense of EE // 2nd edition Logic Gates © 2008 A. Ganago Page 8 of 12
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