Logic Design - Chapter 2: Logic Gates

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  • In OR gate if one of inputs is true the output will be true, and the output will be false if all the input is false.
  • We notice that the output is false when all outputs are false.
  • If any door or any window is opened the Alarm System will do.
  • In AND gate if one of inputs is false the output will be false, and the output will be true if all the input is true.
  • We notice that to make the output true, all the inputs must be true.
  • If the driver is in the car which the Ignition is on and the seat belt is unbuckled the “SEAT BELT ALARM SYSTEM” will do.
  • Not Gate we can get the complement of the input, for example if input == 0 the NOT operation is 1.    if input == A the not is the complement of A which = a’ .
  • NOR operation is the complement of OR operation. If inputs is A , B OR operation is (A+B) but NOR operation is (A+B)’ .
    In NOR operation the output is true when All inputs are false.
    If one of inputs is true, then the output is false.
  • NAND operation is the complement of AND operation. If inputs is A , B OR operation is (AB) but NOR operation is (AB)’ .
    In NAND operation the output is false when All inputs are true.
    If one of inputs is false, then the output is true.
  • The exclusive NOR is the complement of The exclusive OR.
  • Logic Design - Chapter 2: Logic Gates

    1. 1. CHAPTER 2 Logic Gates
    2. 2. Contents          Boolean Variables & Truth Tables OR Operation AND Operation NOT Operation NOR Operation NAND Operation The Exclusive- OR Gate The Exclusive-NOR Gate INTEGRATED CIRCUIT LOGIC FAMILIES 2
    3. 3. Boolean Variables & Truth Tables LOGIC 0 False Off Low No Open Switch LOGIC 1 True On High Yes Close Switch 3
    4. 4. OR Operation 4
    5. 5. Timing Diagrams of OR gates 5
    6. 6. An application: Alarm System 6
    7. 7. AND Operation 7
    8. 8. Timing Diagrams of AND gates 8
    9. 9. An application: A Seat Belt Alarm System -1 -I 9
    10. 10. NOT Operation 10
    11. 11. NOR Operation 11
    12. 12. Negative AND equivalent of a NOR gate 12
    13. 13. An application: An aircraft landing indicator 13
    14. 14. NAND Operation 14
    15. 15. Negative OR Equivalent Operation of the NAND Gate 15
    16. 16. An application: A Manufacturing Plant Tank Indicator The sensors produce a 5 V level when the tanks are more than onequarter full. 16
    17. 17. The Exclusive- OR Gate Inputs A 0 0 1 1 output B 0 1 0 1 X 0 1 1 0 17
    18. 18. The Exclusive-NOR Gate Inputs • equivalence 0 coincidence X-NOR to A 0 0 1 1 output B 0 1 0 1 X 1 0 0 1 18
    19. 19. Timing diagram 19
    20. 20. INTEGRATED CIRCUIT LOGIC FAMILIES Diode Logic (DL)  Resistor-Transistor Logic (RTL)  Diode-Transistor Logic (DTL)  Transistor-Transistor Logic (TTL)  Emitter-Coupled Logic (ECL)  CMOS Logic  20
    21. 21. Fan-in & Fan-out  Fan-in   The number of standard loads drawn by an input to ensure reliable operation. Most inputs have a fan-in of 1. Fan-out  The number of standard loads that can be reliably driven by an output, without causing the output voltage to shift out of its legal range of values. 21
    22. 22. Comparison of performance characteristics of CMOS, TTL and ECL logic gates. Technology Device series Power dissipation: Static At 100 kHz Propagation delay time Fan-out CMOS (silicon gate) 74HC Std : standard Schottky TTL std TTL LS TTL S TTL ALS TTL AS ECL 74 74LS 74S 74ALS 74AS 10KH 1 uW 0.17 mW 8 ns CMOS (metal gate) 4000B 10 mW 10 mW 10 ns 10 2 mW 2 mW 10 ns 19 mW 19 mW 3 ns 1 mW 25 mW 25 mW 1 ns 20 20 20 8.5 mW 8.5 mW 1.5 ns 40 0.1 mW 50 ns LS: Low power Schottky ALS: Advanced Low power Schottky Schottky 1 mW 4 ns S: AS: Advanced 22

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