Difference between Combinational and Sequential circuit

A combinational circuit can be defined as a circuit whose output is dependent only on the inputs at the same instant of time where as a sequential circuit can be defined as a circuit whose output depends not only on the present inputs but also on the past history of inputs.

For a sequential circuit, the values of the variable are usually specified at certain discrete time instants rather than over the whole continuous time. Half Adder, Full Adder, Half Subtractor, Full Subtractor are examples of combinational circuits whereas Flip-Flops, Counters form the sequential circuit.

A sequential circuit consists of combinational circuit and memory elements are connected to it to form a feedback path as shown in the block diagram below:

Sequential circuit block diagramFurther differences between combinational and sequential circuits can be listed as follows:


Combinational Circuit

Sequential Circuit

1. It contains no memory elements It contains memory elements
2. The present value of it’s outputs are determined solely by the present values of it’s inputs The present value of it’s outputs are determined by the present value of it’s inputs and it’s past state
3. It’s behavior is described by the set of output functions It’s behavior is described by the set of next-state(memory) functions and the set of output functions

A sequential circuit can further be categorized into Synchronous and Asynchronous.

Hope you find the information presented here useful. Please leave your footprints in the comments section below for any queries, feedback or suggestions…!!

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    • Thanks Prathyu. We are glad that you find the information useful. Please do let us know if there is any other information that you are looking forward to see at Vertical Horizons. Happy Reading..!!

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  1. Thanks for short and sweet info. its really good info,basic details are given very clearly thanks……….:)

  2. sequential :depends on present input and past output i realized mistake in ur definition in first para graph(past state of input)

  3. please suggest me some good project ideas for my end semester digital logic design project. the benchmark is:
    It should be sequential
    It must contain latches or flip flops

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    I will surely be visiting this website and suggesting it further. I’ll provide my constant feedback regarding the material i would very much appreciate if it were present here.
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