# Difference between Combinational and Sequential Circuit

In digital electronics, logic circuits are classified into two categories namely, combinational logic circuits and sequential logic circuits. The main difference between combination and sequential logic circuits is that a combinational logic circuit does not contain any memory element, while a sequential logic circuit necessarily contains a memory element to store past history of the circuit operation.

In this article, we will discuss combinational logic circuits and sequential logic circuits along with their comparative study.

## What is a Combinational Logic Circuit?

A type of digital time-independent logic circuit in which the output depends on the present inputs only and not on the past operation of the circuit is called a combinational logic circuit. A combinational logic circuit is designed by using different types of logic gates like AND, NAND, NOR, OR, etc. The block diagram representation of a combination logic circuit is depicted in the following figure.

A combinational logic circuit has only a processing circuit and does not have any storing circuit. Therefore, the output of the combinational logic circuit is the function of the inputs at that time.

Combinational logic circuits are widely used in various digital systems to perform various operations like arithmetic operations, data transmission, code conversion, and more. Examples of combinational logic circuits include binary adders, binary subtractors, multiplexers, data comparators, etc.

Thus, combinational circuits do not have a memory element, whereas sequential circuits have a memory element which is the main difference between combinational and sequential circuits.

## What is a Sequential Logic Circuit?

A sequential logic circuit is another type of time-dependent digital circuit having a memory element to store the history of the past operation of the circuit. Therefore, a sequential logic circuit is one whose output depends on the present inputs as well as past outputs.

Sequential logic circuits can be further classified into two types namely, synchronous sequential logic circuits and asynchronous sequential logic circuits. This type of logic circuit is mainly used in high-end applications like processing units, memory units, etc. Examples of sequential logic circuits are counters, finite state machines, registers, etc.

Thus, the sequential circuit has a memory element, and combinational circuits do not have a memory element, which is the main difference between combinational and sequential circuits.

## Difference between Combinational and Sequential Logic Circuits

The important differences between combinational and sequential logic circuits are given in the following table:

Combinational Vs Sequential Circuits

## Conclusion

In conclusion, this is all about combinational and sequential logic circuits and the important differences between them. The combinational logic circuits are fundamental building blocks of all digital circuits while sequential logic circuits are used where complex digital signals processing is required.