Logic gates Symbols and Types

Logic gates 

The gates operation is based on Boolean algebra, which involves variables that have only two possible values: true (1) and false (0).Logic gates are fundamental building blocks used in digital circuits.

“Logic gates are digital circuits or electronic circuits that manipulate voltages, so, in effect, they manipulate the binary ones and zeros which are moving around inside your computer.”

Logic gates, and the innovative ways in which they may be combined, are thus necessary for the proper functioning of a digital computer.

Boolean expression

“The relationship between input and output is called Boolean expression and is represented in binary numbers.”

Binary numbers have only two possibilities. Zero and one. When dealing with the circuits, zero corresponds with the circuit in the off state and one corresponds with the circuit in the on state. 

So, if we are dealing with true or false statements zero is considered false and one is considered true. If you are dealing with voltage an off-state would have zero volts and an on-stage will have a voltage more than zero. 

Types of Logic Gates

There are basically seven types of logic gates which are further classified into three groups:

1- Basic gates
2- Logic gates
3- Arithmetic gates

Basic Gates:

Basic gates are the type of gates that cannot do anything individually. They have to combine with other gates to design a circuit. that is why they are called basic gates because they cannot pass the voltage alone, they have to combine with other gates to complete the circuit.  

Types of Logic Gates:

There are three basic types of logic gates, other types are originated from the basic,  

    1- OR Gate

    2- AND Gate

    3- NOT Gate

    4- NOR Gate

    5- NAND Gate

OR Gate:

OR gate requires two inputs (A, B) and gives one output (Y). The basic logic of this gate is that if at least one input is 1, the output will be 1. The mathematical equation of this gate is:  A + B = output , As in circuit two switches are connected in parallel across a load.

                          OR Gate Symbol and Truth table

AND Gate:

Just like or gate and gate requires single output and two inputs. The output of the gate will be 1 only when all inputs will be 1. The mathematical equation of this gate is: A x B = output, As As in circuit two switches are connected in series across a load.

                         AND Gate Symbol and Truth Table

NOT Gate:

NOT gate consists of one input and one output. The output and input of this gate will be reversed from each other. That is why it is also called the inverter. The mathematical equation of this gate is: A = output (A')

                            NOT Gate Symbol and Truth Table

Universal Gates: 

Universal gates are formed by the combination of two gates. Types of universal 

gates are

• NAND gate

• NOR gate

NAND gate: 

NAND gate essentially operates as an and gate followed by a not gate. that is why it is also sometimes called the ‘NOT-AND’ gate. The output of this gate will be zero only if both of the inputs will be one. The mathematical equation of this gate is

                                          Y = (A . B)’

Symbol: 

                       

Truth Table:

A	B	Y
0	0	1
0	1	1
1	0	1
1	1	0

NOR gate:  

A nor gate is also sometimes called a ‘NOT-OR’ gate, which is essentially, or gate filled by not gate. The output of this gate will be one only if both of the inputs will be zero otherwise the output will be false. The mathematical equation of this gate is

                                        Y = ( A + B )’ 

Symbol: 

                        

Truth table:

A	B	Y
0	0	1
0	1	0
1	0	0
1	1	0

Arithmetic Gates:

Arithmetic gates are the special type of gates that can be used in the half adder, full adder, and subtractor. Types of these gates are

➢    XOR gate

➢    XNOR gate

XOR Gate: 

The XOR gate or ‘Ex-OR’ basically consists of two inputs and one output. The output of this gate will be false if both of the inputs are true. The mathematical equation of this gate is

                                  Y = A’. B + A . B’

Symbol:   

                     

Truth table:

A	B	Y
0	0	0
0	1	1
1	0	1
1	1	0

 XNOR Gate: 

The XNOR gate or ‘Ex-NOR’ accepts only one output but more than one input. The output of this gate will be one if both of the inputs are the same and it will be zero if both inputs are different. The mathematical equation f this gate is

                                    Y = A.B + A’B’

Symbol:

                        

Truth table:

A	B	Y
0	0	1
0	1	0
1	0	0
1	1	1

Logic Gates Usage in Electronics:

Nearly every digital device we use on a regular basis contains logic gates. Such as laptops, smartphones, tablets, memory devices, etc.

Logic gates can be combined in a million different combinations and the number of combinations can be used to make different technologies like robots etc.

Logic gates are basically the main component of a chip that is used in different electronic devices.

Commonly used logic gates are TTL, Transistor-Transistor Logic, CMOS, or Complementary Metal-Oxide-Silicon and chips (ICs)

De-Morgan's Theorem:

De Morgan's theorem explain Boolean algebraic expression. It used in digital designing of logics. first and second theorem explain below as