Difference between combinational and sequential circuit

This article covers the Difference between combinational and sequential circuit. These circuits are important part of digital electronics.

Combinational Circuit

Combinational circuit is a type of circuit whose output depends upon the input provided. It provides instant output and is independent of time. A combinational circuit doesn’t require feedback for further output.

In combinational circuits, only the present input is required. So the performance of the circuit becomes faster  and better when compared to sequential circuit. It has simple circuit and used logic gate as basic building blocks. Combinational circuit can be used in both arithmetic and Boolean  circuit.

Combinational Circuit Diagram

The block diagram for combinational circuit is shown in figure below

Sequential Circuit

Sequential circuit are the type of circuit whose output depends on both current and previous input. The output obtained from the previous input is transferred in the form of feedback and the circuit uses it again for generating next output.

Sequential circuits are slow when compared to combinational circuits. The feedback feature makes the circuit complex. They use flip – flop as basic building blocks of circuit.

Sequential circuit diagram

The block diagram for sequential circuit is shown in figure below

Difference Between Combinational and Sequential Circuit

	Combinational Circuit	Sequential Circuit
1.	In combinational circuits, output depends only upon present input.	In sequential circuits output depends upon both present and previous input.
2.	It has Fast speed.	It has Slow speed.
3.	Combinational circuits can be designed easily.	Sequential circuits are difficult to design when compared to combinational circuit.
4.	These circuit doesn’t have any feedback between input and output.	These circuits have feedbacks between inputs and output.
5.	Elementary building block : logic gate	Elementary building block : flip flop
6.	Used in arithmetic as well as Boolean operation.	Mainly used for storing data.
7.	They nether have clock nor they require triggering.	They are clock dependent and needs triggering.
8.	Combinational circuits don’t have memory element.	Sequential circuit have memory element.
9.	It is easy to handle and use.	It is difficult to handle and use.
10.	Example : 1.    Encoder 2.    Decoder 3.    Multiplexer 4.    demultiplexer	Example : 1.    Flip flop 2.    counter.

Author

Akash Sharma

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Half Adder & Full Adder

Half adder and full adder is a part of combinational circuits. Combinational circuits are those whose output characteristics depends on their input levels at a particular time.