Logic Gates

Index

  1. Logic Gates
  2. Universal Gates
  3. Applications of Logic Gates

Logic Gates

  • Logic gates are the basic building blocks of any digital Circuit.
  • It is an electronic circuit having one or more than one input and only one output.
  • The relationship between the input-output binary variables for each gate can be represented in tabular form by a truth table.
  • Most logic gates take an input of two binary values, and output a single value of a 1 or 0.
  • logic gates can be used in technologies such as smartphones, tablets or within memory devices.

Types of Logic gates

  • AND Gate
  • OR Gate
  • NOT Gate
  • NAND Gate
  • NOR Gate
  • XOR Gate
  • XNOR Gate

AND Gate

The AND gate produces the AND logic function, that is, the output is 1 if input A and input B are both equal to 1; otherwise the output is 0. In other words, the output of this gate is true only when all the inputs are true. Otherwise, the output is "false." A dot (.) is used to show the AND operation A.B.

OR Gate

The OR gate produces the inclusive-OR function; that is, the output is 1 if input A or input B or both inputs are 1; otherwise, the output is 0. In other words, the output is "true" if either or both of the inputs are "true." If both inputs are "false," then the output is "false." The operation performed by an OR gate is represented by a plus (+) sign.

NOT Gate

The NOT gate is an electronic circuit inverts the logic sense of a binary signal. It produces the NOT, or complement, function. It is also known as an Inverter. It reverses the logic state, If the input is 1, then the output is 0. If the input is 0, then the output is 1.

NAND Gate

The NOT-AND (NAND) gate which is equal to an AND gate followed by a NOT gate. The output is "false" if both inputs are "true." Otherwise, the output is "true." The NAND gate is represented by a AND gate with a small circle on the output. The small circle represents inversion.

NOR Gate

The NOT-OR (NOR) gate which is equal to an OR gate followed by a NOT gate. Its output is "true" if both inputs are "false." Otherwise, the output is "false." The NOR gate is represented by an OR gate with a small circle on the output. The small circle represents inversion.

XOR Gate

The Exclusive-OR gate is a digital logic gate with two inputs and one output. The short form of this gate is Ex-OR. It performs based on the operation of the OR gate. If any one of the inputs of this gate is high, then the output of the EX-OR gate will be high. The XOR operation is represented by an encircled plus sign.

XNOR Gate

The Exclusive-NOR gate is a digital logic gate with two inputs and one output. The short form of this gate is Ex-NOR. It performs based on the operation of the NOR gate. When both the inputs of this gate are high, then the output of the EX-NOR gate will be high. But, if any one of the inputs is high (but not both), then the output will be low. The symbol and truth table of the EX-NOR are shown below.

Universal Gates

A Universal gate is a logic gate which can implement any Boolean function without the need to use any other type of logic gate. The NOR gate and NAND gate are universal gates because all the other gates can be created by using these gates. This means that you can create any logical Boolean expression using only NOR gates or only NAND gates.

NAND Gate as A Universal Gate

In the NAND gate, the first part is an AND gate and second part is a dot after it represents a NOT gate. So it is clear that during the operation of NAND gate, the inputs are first going through AND gate and after that the output is reversed and we get the final output.

NOR Gate as A Universal Gate

This is a NOT-OR gate which is equal to an OR gate followed by a NOT gate. The outputs of all NOR gates are low if any of the inputs are high. The symbol is an OR gate with a small circle on the output. The small circle represents inversion.

Applications of Logic Gates

  • NAND Gates are used in Burglar alarms and buzzers.
  • They are basically used in circuits involving computation and processing.
  • They are also used in push button switches. E.g. Door Bell.
  • They are used in the functioning of street lights.
  • AND Gates are used to enable/inhibit the data transfer function.
  • They are also used in TTL (Transistor Transistor Logic) and CMOS circuitry.
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