Introduction to logic gates -

[otw_is sidebar=otw-sidebar-1]in this tutorial we will study Introduction to logic gates.

Digital Logic Gates

Digital systems have been gaining attention for the last few decades due to their benefits over analog circuits. Digital Circuits are less prone to noise and signal processing in digital domain is better than in analog domain. The digital logic gates are fundamental building blocks of the Digital Circuit. These logic gats can be wired in variety of ways to perform the particular task. The three basic digital logic gates are:

These basic digital logic gates can be connected in peculiar ways to form other important logic gates. Logic gates formed by the peculiar combination AND, OR and NOT are:

Introduction to logic gates

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Here the basics of all these logic gates are discussed. Before we start discussion it is important to mention that each basic logic gate implements a particular Boolean operation and these basic logic gates can be connected to implement complex Boolean expressions.

AND Gate:

AND Gate perform the Logic AND operation. Basic AND Gate has two inputs and a single output. The relationship between the inputs and output of the AND Gate is represented by Boolean AND function. The following image shows the truth table, schematic symbol and Boolean Expression of AND Gate.

The AND Operation is represented by . sign. The Output of the AND Gate is HIGH if and only if both of its inputs are HIGH.

OR Gate:

OR Gate performs the Logic OR operation. Basic OR Gate has two inputs and a single output. The relationship between the inputs and output of the OR Gate is represented by Boolean OR function. The following image shows the truth table, schematic symbol and Boolean Expression of OR Gate.

The OR Operation is represented by + sign. The Output of the OR Gate is HIGH if one of the inputs of the OR Gate is HIGH or both of the inputs are HIGH otherwise its output is LOW.

NOT Gate:

NOT Gate is the simplest logic gate with single input and single output. NOT Gate is also referred to as INVERTER and implements the logic NOT Operation. The truth table, schematic symbol and Boolean expression of the NOT Gate are as shown in the following figure:

The Output of the NOT Gate is the complement of its input which is represented by the bar symbol. The output will be HIGH when the input is LOW and vice versa.

NAND Gate:

NAND Gate is formed by connecting output of the AND Gate at the input of the NOT Gate. Thus the NAND Gate is the negation of the AND Gate. The truth table, schematic symbol and Boolean Expression of the NAND Gate are as shown in the following figure:

The output of the NAND Gate is LOW if and only if both of its inputs are HIGH otherwise the output is HIGH. Note that the truth table of the NAND Gate is complement of the AND Gate.

NOR Gate:

NOR Gate is formed by connecting output of the OR Gate at the input of the NOT Gate. Thus the NOR Gate is the negation of the OR Gate. The truth table, schematic symbol and Boolean Expression of the NOR Gate are as shown in the following figure:

The output of the NOR Gate is HIGH if and only if both of its inputs are LOW otherwise the output is LOW. Note that the truth table of the NOR Gate is complement of the OR Gate.

XOR Gate:

The XOR Gate is formed by connecting the AND, NOT and OR in particular configuration. XOR Gate is the two input and single output logic gate. The truth table, schematic symbol and Boolean expression the XOR Gate is as shown in the following figure:

The Output of the XOR Gate is HIGH when both of its inputs are different otherwise the output is LOW. The XOR Gate is commonly used in Full Adder, Half Adder circuit. The XOR Gate is also used in the comparator circuit.(Introduction to logic gates)

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XNOR Gate:

Like XOR Gate XNOR Gate is also formed by the combination of basic Gates. XNOR Gate is the complement of the XOR Gate. The truth table, schematic symbol and Boolean Expression of the XNOR Gate is as shown in the following figure:

The output of the XNOR Gate is HIGH if and only if both of the inputs are same otherwise the output is LOW. Note here that the truth table of the XNOR Gate is the complement of the XOR Gate.

Logic Gates Truth Table

Logic Gates Applications

Universal Logic Gates

nand and nor are universal logic gates

Logic Gates Project

7 segment display circuit using logic gates

here is the circuit of driving 7 segment display with different logic gates

i Download this simulation following link

https://www.youtube.com/channel/UCrJHI1mvySmAJ_97eYAZnhA/videos

Components of digital clock using logic gates:

The Components of digital clock using logic gates shown in the following

7 segment display
Ic-cd4026
Ic –cd4017
Ic-4073
Transistor –MPS6514 OR Equivalent(BC547)
Diode 1N4148
Resistor – 1k,330ohm,220k,100ohm,10k
Push button
Battery

Note: in practical you need to design 1Hz pulse generator and add with this circuit