Introduction to NOT Gate:
Digital logic gates are the building blocks of the digital circuit. Each basic logic gate implements a unique Boolean function and a complex Boolean expression is implemented using the network of basic gates. Three basic logic gates are:
- AND Gate.
- OR Gate.
- NOR Gate.
NOT Gate implements the NOT Boolean function and similarly AND and OR Gates implements the AND and OR functions respectively. Here the discussion will be oriented around the NOT Gate only.
NOT Gate is one of the basic logic gates that implement the logical NOT operation. NOT Gate is single-input single-output Gate and commonly referred as Inverter as it inverts its input; the output of the NOT Gate is complement of its input. The operation of the NOT Gate is simplest among all basic gates. The Boolean expression that represents the logical conjunction and thus represents the functionality of the NOT Gate is as shown below:
The NOT function is represented by the ‘BAR’ sign as shown above. The BAR represents that the output of the NOT Gate will be the complement / inverse of its input. As in the case of AND and OR Gate the input of the NOT Gate is the Binary Variable which means that it can assume one of the two value that ‘0’ or ‘1’. Similarly the output will be either ‘0’ or ‘1’ depending on the input. If the input of the NOT Gate is ‘HIGH’ the output will be ‘LOW’ and vice versa.
Truth Table of NOT Gate:
The relation between the state of the output and that of the inputs is represented in the form of the table. This table is called the Truth Table. The Truth Table of the NOT Gate along with its schematics symbol is shown below:
NOT Gate Symbol
As shown in the truth table when the input of the NOT Gate is LOW its output is HIGH and similarly when the input of the NOT Gate is HIGH the output will be LOW. In terms of Positive Logic ‘1’ is considered to be ‘HIGH’ and ‘0’ is considered as ‘LOW’ and in terms of Negative Logic ‘1’ is considered as ‘LOW’ and ‘0’ is considered to be ‘HIGH’. The bubble at the output of the NOT Gate represents the logical inversion.
NOT Gate Circuit:
Now let us understand the circuit that implements the NOT Gate. NOT Gate can be implemented in a variety of ways depending upon the electronic components used to design the circuit. For example diodes, transistors, resistors and combination of these components can implement the NOT Gate. The most popular techniques for designing the NOT gates are TTL (Transistor-Transistor Logic) and CMOS (Complementary Metal Oxide Semiconductor Transistor) logics. An example of the circuit implementing the NOT Gate is shown in the figure below:
The input of the NOT Gate is connected at the base of the transistor and the output is taken from the collector. The transistor here acts as the switch so when the voltage is applied at the base of the transistor the transistor starts conducting and shorts the output to the ground similarly when no voltage is applied at the input the output is connected to the Vcc as shown thus in this way the circuit implements the NOT function.
NOT Gate IC Number:
NOT gates are available in the IC packages. One of the most popular IC for NOT Gate is 7404 which is a HEX-single input NOT Gate IC which means that this IC contains 6 independent NOT Gates. The pinout and connection diagram of the 7404 IC is shown below:
That is all for now I hope this article would be helpful for you in the next article I will come up with XOR gate. Stay connected, keep reading and enjoy learning.