Logic Gate Symbol

Logic gates are the fundamental building blocks of digital circuits. They perform basic logical operations on one or more binary inputs and produce a single binary output. Here are the common logic gates and their symbols in different standards (commonly used in IEEE and IEC standards):

1. AND Gate

  • Function: An AND gate produces a high output (1) only when all of its inputs are high (1). If any input is low (0), the output is low (0).
  • Symbol:
    • IEEE Standard: It is represented by a shape that looks like a D - shaped block with multiple input lines on the left - hand side and a single output line on the right - hand side. For a two - input AND gate, there are two input lines entering the left side of the block, and one output line leaving the right side.
    • IEC Standard: The symbol is a rectangular - shaped block with the input lines on the left and the output line on the right. The AND function is often indicated by a dot or the word “AND” inside the block.

2. OR Gate

  • Function: An OR gate produces a high output (1) if at least one of its inputs is high (1). It only produces a low output (0) when all inputs are low (0).
  • Symbol:
    • IEEE Standard: It has a shape similar to a rounded - cornered block with multiple input lines on the left and a single output line on the right.
    • IEC Standard: It is a rectangular block with input lines on the left and an output line on the right. The OR function is usually indicated by a plus sign or the word “OR” inside the block.

3. NOT Gate (Inverter)

  • Function: A NOT gate has a single input and produces the opposite logic level at its output. If the input is high (1), the output is low (0), and vice versa.
  • Symbol:
    • IEEE Standard: It is represented by a small triangle with a circle at the output. The input line enters the flat side of the triangle, and the output line leaves from the pointed side with the circle, which indicates inversion.
    • IEC Standard: It is also a triangle - like shape with a circle at the output to denote the inversion operation.

4. NAND Gate

  • Function: A NAND gate is the combination of an AND gate followed by a NOT gate. It produces a low output (0) only when all of its inputs are high (1), and produces a high output (1) in all other cases.
  • Symbol:
    • IEEE Standard: It is similar to the AND gate symbol, but with a circle at the output to indicate the inversion.
    • IEC Standard: It is based on the AND gate symbol in the rectangular block, with a circle at the output to show the NOT operation.

5. NOR Gate

  • Function: A NOR gate is the combination of an OR gate followed by a NOT gate. It produces a high output (1) only when all of its inputs are low (0), and produces a low output (0) if at least one input is high (1).
  • Symbol:
    • IEEE Standard: It is similar to the OR gate symbol, but with a circle at the output to indicate the inversion.
    • IEC Standard: It is based on the OR gate symbol in the rectangular block, with a circle at the output for the NOT operation.

6. XOR Gate (Exclusive - OR Gate)

  • Function: An XOR gate produces a high output (1) when the number of high inputs is odd. That is, it produces a high output if the inputs are different and a low output if the inputs are the same.
  • Symbol:
    • IEEE Standard: It has a shape similar to a modified OR gate symbol, often with an additional curved line on the input side to distinguish it from the OR gate.
    • IEC Standard: It is a rectangular block with input lines on the left and an output line on the right. The XOR function is usually indicated by a plus sign inside a circle or the word “XOR” inside the block.
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