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Logic Gates

🏠 Main | 🔧 Hardware | ⚡ Basic Components | 🖥️ Processors

Overview

Logic gates are the fundamental building blocks of digital circuits. They perform basic logical operations on binary inputs (0 and 1) to produce binary outputs.

Basic Logic Gates

AND Gate

  • Function: Output is 1 only when ALL inputs are 1
  • Symbol: D-shaped with flat input side
  • Truth Table: 
    A | B | Output
0 | 0 |   0
0 | 1 |   0
1 | 0 |   0
1 | 1 |   1

OR Gate

  • Function: Output is 1 when ANY input is 1
  • Symbol: Curved input side, pointed output
  • Truth Table: 
    A | B | Output
0 | 0 |   0
0 | 1 |   1
1 | 0 |   1
1 | 1 |   1

NOT Gate (Inverter)

  • Function: Output is opposite of input
  • Symbol: Triangle with circle at output
  • Truth Table: 
    A | Output
0 |   1
1 |   0

Derived Logic Gates

NAND Gate

  • Function: NOT AND - Output is 0 only when ALL inputs are 1
  • Importance: Universal gate - can create any other gate
  • Truth Table: 
    A | B | Output
0 | 0 |   1
0 | 1 |   1
1 | 0 |   1
1 | 1 |   0

NOR Gate

  • Function: NOT OR - Output is 1 only when ALL inputs are 0
  • Importance: Also a universal gate
  • Truth Table: 
    A | B | Output
0 | 0 |   1
0 | 1 |   0
1 | 0 |   0
1 | 1 |   0

XOR Gate (Exclusive OR)

  • Function: Output is 1 when inputs are different
  • Uses: Binary addition, comparison circuits
  • Truth Table: 
    A | B | Output
0 | 0 |   0
0 | 1 |   1
1 | 0 |   1
1 | 1 |   0

Implementation

  • Transistor Level: Gates built from combinations of transistors
  • IC Packages: Multiple gates in single integrated circuits
  • Logic Families: TTL, CMOS, ECL with different characteristics

Applications in Computing

  • ALU (Arithmetic Logic Unit): Performs calculations using gate combinations
  • Memory Circuits: Store and retrieve binary data
  • Control Logic: Manage processor operations
  • Address Decoding: Select memory locations

Boolean Algebra

  • Mathematical foundation for logic gate operations
  • Rules for simplifying logic expressions
  • De Morgan's Laws for converting between gate types
  • Karnaugh Maps for optimization

Practical Considerations

  • Propagation Delay: Time for output to change after input change
  • Fan-out: Number of inputs a gate output can drive
  • Power Consumption: Energy used by gate operation
  • Noise Immunity: Resistance to electrical interference