Electronics have a wide type of circuitry in it, for handling the signals in an efficient way. Semiconductors play a very important role in it and due to its very compact size and high processing speed, it is useful in controlling the logic in a reliable way.
Two things thus play an important role in electronics – semiconductors and how the logic is written inside to execute the coding. Electronic circuits inside are generally classified into two categories – combinational and sequential.
In this post, we will learn the difference between combinational circuits and sequential circuits.
What is a Combinational Circuit?
Any circuit has an input and output. When it receives an input, the processor computes the input and produces an output accordingly. A combinational circuit is a simple example of this type. As the name suggests, it acts on various combinations of inputs and produces an output. Suppose, consider two simple gate logics – OR / AND. OR means it will generate an output if any of the two inputs turn on. If all the inputs are off, then it will not generate an output. AND means it will generate output if all the inputs are on. If any of the input goes off, then it will not generate an output. So, it basically works on real-time feedback. What is the current status of input, output will be given accordingly. This is a combinational circuit.
A combination circuit, as discussed, works on the present condition of the input and gives an output accordingly. This circuit does not have any memory for processing. Because, if it has memory, then it would have not been dependent on the input every time. It does all the operations without memory. Popular examples of combinational circuits are logic operators, arithmetic operators, comparators, multiplexers, and de-multiplexers.
What is a Sequential Circuit?
A sequential circuit is a further extension of a combinational circuit. Where a combinational circuit did not have memory, a sequential circuit has memory in it. As the name suggests, it too acts on various combinations of inputs and produces an output. But when an input goes off, it is the task of this circuit to memorize and act accordingly. When the input is received again, it will perform another task.
Suppose take an example of a counter. When an input is received, the count increments. When the input goes off, the count is hold to its last state. And when the input is received again the count increments. Thus, it has memorized the count and when the set counts are achieved, it generates an output. This would not have been possible in a combinational circuit. This is the function of a sequential circuit.
A sequential circuit, as discussed, works on the logic written inside for processing the inputs in any state and gives an output accordingly. This circuit has a memory for processing. Because, if it did not have memory, then it would have been dependent on the input every time. It does all the operations with memory. Popular examples of combinational circuits are processors, counters, registers, shift instructions, and rotate instructions.
Difference Between Combinational and Sequential Circuit
- The first and foremost difference is memory presence. A combinational circuit does not have memory in it, whereas a sequential circuit has memory in it.
- The processing speed in a combinational circuit is very fast than a sequential circuit.
- The combinational circuit is easy to design and operate than a sequential circuit.
- A combinational circuit cannot be used in very complex operations, as compared to a sequential circuit.
- The combinational circuit does not require a clock, as it works in present conditions.
- The sequential circuit requires some sort of feedback for processing; which means previous input and current input type. Output generated from previous input is used as feedback for the next input that will come and will process accordingly.
- A combinational circuit depends on logic gates, whereas a sequential circuit depends on flip flop and other elementary blocks.
In this way, we saw the difference between combinational and sequential circuit.
