from Ch 23 Logic Gates-2

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

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