Logic gates are small digital switching circuit that determines the output of two or more inputted functions in Binary format. Logical ‘1’ means ‘True’ or ‘High’ in nature, whereas logical ‘0’ means ‘False’ or ‘Low’ in nature. Based on different logical operations, the output differs. There can be many inputs in a logic gate but there will be only one output. Each logic gate has its own truth table which represents all the combinations of input and output.

What is an AND Gate?

AND gate is the fundamental logic gate that executes the logical multiplication of binary input. The AND operation is carried out in the same way as standard multiplications of 1s and 0s. An AND gate is a logic circuit that performs AND operations on the input of the circuit. When all the inputs are 1, the AND Gate outputs 1, otherwise it outputs 0. A dot (.) denotes the AND operation.

Operation of AND Gate

AND Gate takes values as input and returns –

Returns 1, if all the inputs are 1.

Returns 0, if all inputs are not 1.

The expression of AND Gate is as follows –

Say we have two inputs, A and B and the output is called X, then the expression is:

X = (A . B)

Types of AND Gates

There are two types of AND gates, based on the number of inputs

2-Input AND gate

It takes 2 inputs and the truth table will have 2² = 4 possible combinations. The truth table of 2 input AND gate is as follows:

X=A⋅B

3-Input AND Gate

It has three inputs and only one output. There are 2³ = 8 combinations of input and output.

X=A⋅B⋅C

Symbol of AND Gate

Given Below is the Symbol of AND gate, A and B represent the two inputs. The AND gate performs the logical AND operation on the inputs. The output is represented by the line extending from the bottom of the AND gate symbol.

AND Gate With Truth Table

Truth Table of AND Gate

In the given truth table When both inputs A and B are 0, the output is 0.If either input A or B is 0 while the other is 1,the output is 0.Only when both inputs A and B are 1,the output is 1.This behavior reflects the AND gate’s logical operation, where the output is true (1) only when all inputs are true (1).

3 input AND gate

AND Gate in Terms of Transistor

The AND gate is one of the main building blocks of Digital Logic Circuits. Its operation can also be explained via the concept of transistors

AND gate representation in terms of Transistor

In the above diagram, transistor will act as a switch. When we apply the voltage through a collector terminal, the voltage reaches to emitter terminal when base terminal voltage between 0 and collector voltage.

Let us take an example when both the inputs are 0. When the voltage is supplied through the collector terminal of transistor Q1, emitter terminal does not receive any input value because base terminal value is 0. Similarly, emitter of Q1 is connected to collector of transistor Q2, provides no current or voltage. Hence the emitter output of transistor 2 is 0 and as a result final output (Q) is also 0.

Applications of AND Gate

• It is used to design complex circuits such as adders, multipliers, etc.
• It is used in controlling the traffic light system. For example: Green light should be activated when all the roads are clear.
• It can be used in security system, where AND gate can be used to activate an alarm when a lots of sensor are operated.
• It can be used in error detection and error correction technique.

Advantages of AND Gate

• It performs logical conjunction operation. It means that, it produces an output ‘1’ when all its input are ‘1’.
• It consumes low power as compared to any other complex logic gate.
• It is very easy to implement using CMOS, TTL and many more.

Disadvantages of AND Gate

• AND gate has limited output range. This means it will give high output when all the inputs are high else it will give low output.
• It introduces the propagation delay which might lead to synchronization issues.

Solved Example

A person wants to build the home security system. The logic is when the door is open and motion is detected by the motion sensor, then alarm should start beeping. What logic he should build and which logic gate he can use?

Solution: Lets build the truth table table:

Let us assume, door status is ‘1’ when open and ‘0’ when close.

Also, motion sensor status is ‘1’ when motion is detected else ‘0’.