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Chapter - 8: Logic Gates

A logical gate is a physical component through which we can perform logic operations. It is a decision-making element. Logic gate is the basic element of combinational logic circuits

Types of Gates

  1. AND gate
  2. OR gate
  3. NOT gate
  4. XOR gate
  5. NAND gate
  6. NOR gate
  7. XNOR gate
  8. Buffer Gate
  1. AND gate

    AND gate performs logical multiplication. This gate has 2 or more than 2 inputs and 1 output. The output of this gate is will be logical 1 whenever all inputs are logical 1.the output of this gate will be logical 0 whenever any input is logically 0

    Boolean Expression

    Logical Symbol

    Truth Table

  2. OR gate

    The OR gate performs logical addition. This gate has 2 or more than 2 inputs and 1 output. The output of this gate will be logical 1 whenever any OR all inputs are logical 1’s and whenever all inputs are logical 0, then output will be logical 0.

    Boolean Expression

    Logical Symbol

    Truth Table

  3. NOT gate

    This gate has only one output. This gate performs complement. The output of this gate will be logical '1' when input is logical '0'. And when input is logical '1' then this gate provides output logical '0'.

    Truth Table

    Logic Symbol

    Boolean Expression

  4. XOR gate (Exclusive OR Gate)

    This gate performs odd functions. This gate has two or more than two inputs and one output. The output of this gate will be one whenever their inputs have odd number of 1’s, otherwise the output of this gate will be zero.

    XOR Operation

    Boolean Expression

    Truth Table

    Logical Symbol

  5. NAND gate

    The NAND gate performs the complement of AND gate operation. This gate has two or more than two inputs and one output. The output of this gate will be one whenever any input is 0. Thus, whenever all inputs are 1’s then output of this gate will be 0.

    Truth Table

    Logic Symbol

  6. NOR gate

    The NOR gate performs complement of OR operation. This gate has 2 or more than 2 inputs and 1 output. The output of this gate will be 1 when all inputs are 0 and whenever any input is 1 then output of this gate will be 0.

    Truth Table

    Logic Symbol

  7. XNOR gate (Exclusive NOR gate)

    This gate performs complement of XOR operation. This gate has two or more than two inputs and 1 output. The output of this gate will be 1 whenever their inputs have odd numbers of 1’s then the output of this gate will be 0. That’s why this gate performs even functions.

    Truth Table

    Logic Diagram

  8. Buffer Gate

    The buffer gate has only one input and 1 output. The purpose of this gate has to process the input. The output of this gate will be 1 when input is 1. And when input is 0 then output of this gate will be zero.

    Truth Table

    Logic Symbol

    Boolean Expression

Problems:

Draw the logical digaram of the following:
  • X = AB + BC + AC
  • Solution: