Learn Logic Circuits – Digital Design Step by Step for Beginners

Introduction

Your Computers, Smartphones, for that matter, your daily-use washing machines work on Logic Circuits. Logic circuits enable machines to make decisions automatically and perform what is expected of them. No Logic circuits, no machines possible. Are you not interested in learning about logic circuits? And how do they help the digital technology work? You are in the right article to learn everything about logic circuits easily, step by step.

As such, one can say that the heart of digital electronics is Logic circuits. The logic circuits process the input information, make decisions and give appropriate output in all digital electronics devices.

What is a Logic Circuit?

The electronics circuit that works with just two values, namely 0 and 1, is called a logic circuit. 0 and 1 are called binary numbers in digital electronics. The meaning of the binary numbers in digital electronics is as follows:
‘0’ represents OFF, LOW, NO, or FALSE
‘1’ represents ON, HIGH, YES, or TRUE
The details are tabulated for ease of viewing and for clarity.

0	1
OFF	ON
LOW	HIGH
NO	YES
FALSE	TRUE

Today, we intend to discuss the logic circuits – all about Logic elements, the most basic items for the set-up of logic gates, with illustrations. Hence, friends, pay your kind attention to learn the intricacies of the elements thoroughly, as it is the basic foundation for the Logic Circuits. Both Raju and Gopu showed curiosity to learn logic gates tutorials in depth for building sound knowledge and develop skills in building digital electronics project after their studies are over. 

Logic circuits

‘Logic gates‘ are the basic building blocks of digital electronics. Your computers, calculators, smartphones, traffic lights and digital clocks are all work under the principles of logic gates. The given inputs help to make decisions for their performance. As such thorough understanding of logic gates is the primary essential tutorial to learn digital electronics.

Logic elements are the basic circuits by which all digital equipment, simple or complex, is built. There are two basic types of digital logic circuits in the system. They are classified as ‘decision making’ and ‘memory’ circuits.
Decision-making elements monitor the binary inputs and produce outputs based on the input states and operational characteristics of the logic elements.
Memory elements are used to store binary data.
We are going to discuss each elaborately in our coming posts, as they are the backbone of logic gates.

Logic gates

There are three basic decision-making elements in digital electronics. The three elements are

• • The AND Gate

• • The OR Gate and

• • The NOT Gate (INVERTER gate / Negation)

These gates are quite simple compared to the fundamental mathematical calculations like addition, subtraction etc. We intend to focus attention on practical applications of this system of logic. in the form of circuits.

For the practical implementation of these gates, it is always necessary that we clearly define the logic states of the circuit.
For example, ‘0v/5v’ or switch ‘open/closed’ states should be clearly attributed to the binary numbers ‘0 and 1’.

A logic gate is an electronic circuit that performs a logical operation on one or more binary inputs and produces a single binary output. Here, the input values are 0 or 1. The output values are also 0 or 1.
It is important that we understand that the Digital systems do not understand numbers like 2, 3, 5, or 10 directly. It can only understand 0 and 1. Hence, this binary number system is known as ‘binary logic’. As this binary logic is employed in logic circuits, they are known as logic gates.

Types of logic gates

There are seven types of logic gates in the digital system.

• • AND Gate

• • OR Gate

• • NOT gate

• • NAND Gate

• • NOR Gate

• • XOR Gate

• • XNOR Gate

As we discussed earlier, the first three gates are the basic, fundamental logic circuits. The other gates are simply the complex systems based on the fundamental logics.

Further, these gates can be categorised into three types

• • AND,OR and NOT are Basic gates

• • NAND and NOR are Universal gates

• • XOR and XNOR are Comparison logic gates

Let us briefly study the comprehensive information about these Logic Gates in a tabular form so that the details will be distinct and easy to understand. 

LOGIC GATES AT A GLANCE

S.No	Logic Gate	Symbol	Logic Function	Truth Table
1	AND Gate		Gives output 1 only when all inputs are 1.	Input A Input B  Output 0                 0             0 0                 1              0 1                  0             0 1                   1             1
2	OR Gate		Gives output 1 if at least one input is 1.	Input A Input B  Output 0                   0                0 0                   1                 1 1                    0                1 1                     1                1
3	NOT Gate		Changes the input into the opposite value.	Input     Output 0                1             1                 0
4	NAND Gate		Gives output 0 only when all inputs are 1.	Input A  Input B   Output 0                  0               1 0                  1                1 1                   0               1 1                   1               0
5	NOR Gate		Gives output 1 only when all inputs are 0.	Input A Input B  Output              0                   0               1 0                   1               0 1                    0              0 1                    1               0
6	XOR Gate		The output becomes 1 only when the inputs are different.	Input A Input B  Output 0                    0            0 0                    1             1 1                     0            1 1                     1             0
7	XNOR		The output becomes 1 only when both inputs are the same.	Input A  Input B  Output 0                 0              1 0                 1               0 1                  0              0 1                  1               1

Types of Logic Circuits

In digital electronics, there are two main types of Logic Circuits functioning. They are
1. Combinational Logic circuits
2. Sequential Logic Circuits
Let us try to understand each type as they are widely used in our day-to-day digital electronics service.

Combinational Logic circuits

The output of these circuits depends only on the present inputs or current inputs. As such, they do not store any data. A few example circuits are worth considering. The are:

• Adders
• Subtractors
• Multiplexers
• Encoders
• Decoders

Sequential Logic circuits

These circuits can store information and the output depends on the ‘present inputs’ as well as ‘previous outputs’. As such, these circuits utilise memory elements like ‘flip-flops.’ Some of the important circuit examples are given below.

• Counters
• Registers
• Memory Devices
• Digital Clocks.

Application of Logic gates

As we said earlier, the Logic gates are made use of in every digital electronic appliances. Computers, Calculators, digital clocks, smart phones, washing machines, security systems, traffic lights and in robotic machines make use of the logic gates in their functional systems.

To sum up

With just two values  0 and 1, the whole digital techniques are managed to perform its specific functions. Logic gates are the real decision makers in controlling the digital word. Hence logic gates are the real building blocks for the digital systems.  

Having discussed thoroughly on the logic gates, we are going to further elaborate each and every gates in depth in our coming posts. As such please ensure great attention and study the deliberations to acquire correct knowledge and skill in digital electronics field.