# Sequential and Combinational Circuit || Combinational Circuit || Bcis Notes

Sequential circuit

A sequential circuit is the assimilation of a combinational logic circuit and a storage element. With the applied inputs to the combinational logic, the circuit outputs are derived. Although every digital system is likely to have a combinational circuits, most systems encountered in practice  also include memory elements, which requires that the system be describes in term of sequential circuit.

The Block diagram for sequential circuit is given below: Combinational Circuit

In digital circuit theory, a combinational logic is a type of digital logic which is implemented by Boolean circuit, where the output is a pure function of the present input only. This is in contrast to sequential logic in which the output depends upon not only on the present input but also on the history of input.

The block diagram of combinational circuit is given below: Difference between these two circuits is given below:

S. N. Keys Combinational Circuit Sequential Circuit
1 Definition Combinational Circuit is the type of circuit in which output is independent of time and only relies on the input present at that particular instant. On other hand Sequential circuit is the type of circuit where output not only relies on the current input but also depends on the previous output.
2 Feedback In Combinational circuit as output does not depend on the time instant, no feedback is required for its next output generation. On other hand in case of Sequential circuit output relies on its previous feedback so output of previous input is being transferred as feedback used with input for next output generation.
3 Performance As the input of current instant is only required in case of Combinational circuit, it is faster and better in performance as compared to that of Sequential circuit. On other hand Sequential circuit are comparatively slower and has low performance as compared to that of Combinational circuit.
4 Complexity No implementation of feedback makes the combinational circuit less complex as compared to sequential circuit. However on other hand implementation of feedback makes sequential circuit more complex as compared to combinational circuit.
5 Elementary Blocks Elementary building blocks for combinational circuit are logic gates. On other hand building blocks for sequential circuit are flip flops..
6 Operation Combinational circuit are mainly used for arithmetic as well as Boolean operations. On other hand Sequential circuit is mainly used for storing data.

Therefore these are some difference between sequential and combinational circuit.

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