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:

Further differences between combinational and sequential circuits can be listed as follows:

S.No.	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…!!

Neha Mishra on September 8, 2011 at 8:31 PM said:

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- Admin on September 8, 2011 at 9:14 PM said:
  
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- Deepak Jaswal on November 21, 2012 at 8:24 PM said:
  
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Biji Nair on September 15, 2011 at 10:18 AM said:

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- Admin on September 15, 2011 at 2:18 PM said:
  
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- Admin on December 21, 2011 at 12:48 PM said:
  
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.v.k on October 30, 2011 at 1:38 PM said:

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- Admin on December 21, 2011 at 12:48 PM said:
  
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kipronoh on November 3, 2011 at 12:37 PM said:

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Rabiya Rahim on November 10, 2011 at 7:44 PM said:

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Debajyoti on November 28, 2011 at 11:03 PM said:

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kuku on December 11, 2011 at 2:51 PM said:

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- Admin on December 21, 2011 at 12:40 PM said:
  
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raheel abbasi on February 11, 2012 at 5:55 AM said:

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Brian WaMan on March 11, 2012 at 6:23 PM said:

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- Admin on March 18, 2012 at 10:41 PM said:
  
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- Admin on May 16, 2012 at 8:49 AM said:
  
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Marie on May 21, 2012 at 12:43 AM said:

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- Admin on May 23, 2012 at 4:34 PM said:
  
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kd on August 5, 2012 at 11:19 AM said:

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huei on January 13, 2013 at 8:53 PM said:

It’s already a good differentiation
but will better if given some more diagram between both circuit
thanks a lot
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Bernard on January 31, 2013 at 6:45 PM said:

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Thanks good job.
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thasneem on February 9, 2013 at 6:11 PM said:

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