Logic gates are basic building blocks of any digital circuits. Most of electronic devices have some form of logic gates inbuilt in them. In Digital electronics, logic circuits with one or more inputs and one output forms a gate. Gates are also available in the form of Integrated Circuits (ICs)

• Basic gates include: AND, OR, NOT, NAND, NOR, XOR, XNOR.

Detailed Description:

AND Gate: This gate performs logical multiplication operation. Here the output is low when either of input is low and high when both the inputs are high. Basic Transistor- transistor logic (TTL) AND gate IC is 7408 (pin diagram depicted below) it is named as quad 2 input AND gate IC as it contains 4 nos. of AND gates.
Logic Expression: Y= A.B

OR Gate: This gate performs logical addition operation. Here the output is low when both the inputs are low and high when either of the input is high. Basic TTL OR gate IC is 7432 (pin diagram depicted below) it is named as quad 2 input OR gate IC as it contains 4 OR gates.
Logic Expression: Y= A + B

NOT Gate: This logic gate performs the function for switching from one logic level to another i.e. complementation. Basic NOT gate IC is 7404 (hex inverter).
Logic Expression: Y= Ā

NAND Gate: It is nothing but an AND gate followed with a NOT gate. It is termed as Universal gate. Its output is low if all the inputs are in logic high. Basic IC for NAND gate is 7400.
Logic Expression: Y= A • B

NOR Gate: It is nothing but an OR gate followed with a NOT gate. It is termed as Universal gate. Its output is high if all the inputs are in logic low. Basic IC for NOR gate is 7402.
Logic Expression: Y= A + B

XOR Gate: It is also termed as exclusive OR gate and may be used as programmable inverter. Its output is high if and only if one of the inputs is logic high. Basic IC for XOR gate is 7486.
Logic Expression: Y= A ⊕ B =(AB) + (AB)

XNOR Gate: It is XOR gate followed with NOT gate and is also termed as equivalence gate. Its output is high if both of the inputs are either logic high or logic low. Basic IC for XNOR gate is IC 74266
Logic Expression: Y= A ⊙ B = A ⊕ B = AB + A B

To understand the functioning of a gate, follow the steps below:

Steps:

1. Select a gate to study, for example: NOT gate.
2. Now pick the input, click on it and extend the connection to input of the gate.
3. Now pick the output, click on it and extend the connection to output of the gate.
4. Double Click on input to change its state from logic 0 to 1 and vice-versa and see the output to understand the functioning of the particular gate..

Note: For other gates that require 2 inputs (AND, OR, NOR, NAND, XOR and XNOR), pick two inputs and follow steps 2 to 4.

To access Boolean expression on the simulator tab, follow the steps below:

1. Click the Toggle button near IC to enable/disable IC.
2. Once IC is disabled, Boolean expressions become accessible.
3. Clicking on a Boolean expression will show its truth table on the screen.
4. Now follow the below instructions for each Boolean expression respectively:

For Boolean expression: Y= AB + AB’

Steps:

1. Select Inputs
2. Select AND gate and connect inputs (AB)
3. Select NOT gate to compliment the input
4. Select another AND gate and connect inputs (AB̅)
5. Select OR gate and connect the output of AND gates to its input
6. Connect output at OR gate and see the output according to the truth table as shown.

For Boolean expression: Y= (A+B).(A’+B)

Steps:

1. Select Inputs
2. Select OR gate and connect inputs (A+B)
3. Select NOT gate to compliment the input
4. Select another AND gate and connect inputs (AB̅)
5. Select another OR gate and connect inputs (A̅+B)
6. Select AND gate and connect the output of OR gates to its input
7. Connect output at AND gate and see the output according to the truth table as shown.