| This logic gate, sometimes referred to as an inverter, is the only one in that has a single input. Its input goes into the left side of a triangle symbol while its output exits the gate through a small circle placed at the tip of the opposite corner. Note that it is the small circle that defines the operation of this gate, so it should not be left out. | |
| The NOT gate is used to flip the value of a digital signal. In other words, it changes logic1 input to logic0 or it changes logic0 input to logic1. An example of an inverter might be the light detection circuit used to control the automatic headlights of a car. | |
| During the daylight hours, sunshine enters the light detector which is typically installed on the top surface of the car’s dashboard. This acts as logic1 input. Since it is daytime, the headlights need to be turned off, logic0. When the sun goes down and no light enters the light detector, logic0, then the headlights must be turned on, logic1. | |
| The NOT operation is unlike the OR and AND operations in that it can be performed on a single input variable. For example, if the variable A is subjected to the NOT operation, the result x can be expressed as | |
| x = A’ | |
| where the prime (‘) represents the NOT operation. This expression is read as: x equals NOT A x equals the inverse of A x equals the complement of A |
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| Each of these is in common usage and all indicate that the logic value of x = A’ is opposite to the logic value of A. | |
| The truth table of the NOT operation is as follows: | |
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| 1′ = 0 because NOT 1 is 0 0′ = 1 because NOT 0 is 1 |
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| The NOT operation is also referred to as inversion or complementation, and these terms are used interchangeably. |
