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Logic Gate

Last updated: June 8, 2014

What Does Logic Gate Mean?

A logic gate is an assortment of electronically controlled switches that implement Boolean logic processes. The process consists of a logical operation on one or more logical inputs that generates a solitary logic output.

A logic gate is comprised of resistors and transistors, or diodes. They can perform simple or highly complex operations by joining a variety of logic gates. The maximum number of logic gates is limited to the size of the integrated circuit (IC) divided by the size of logical gates. Generally, smaller transistors generate faster central processing units (CPU) and a more complex system. However, as IC technology improves, fewer logic gates are needed.


Techopedia Explains Logic Gate

Integrated circuits may include a few or millions of logic gates, like a microprocessor. The majority of logic gates have two inputs and one output. The input and output are either in a state of zero or one, depending on the voltage. Zero, or low state, is around zero volts and one, or high state, is around +5 volts.

Every logic gate has two inputs - A and B - excluding NOT. Each input may have a value of zero, which is false, or a value of one, which is true. The output is a single value of zero or one, depending on the logic. The logic gate truth table is as follows:

  • AND: True if A and B are both true
  • OR: True if A or B are true
  • XOR: True if either A or B are true, false if both are true
  • NOT: Inverted; false if input is true, true if input is false
  • NAND: AND followed by NOT; false if both A and B are true
  • NOR: OR followed by NOT; true if both A and B are false
  • XNOR: XOR followed by NOT; true if A and B are both true or both false

Because logic gates are physical, properties cannot be articulated in a truth table, such as gate delays. A gate delay is the amount of time for the output to change while the input changes. This time is not zero; thus, a small amount of time elapses before the output proceeds.


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