Difference Between Combinational Circuit and Sequential Circuit
Introduction
In digital electronics, circuits are classified into two types: combinational circuit and sequential circuit. While both circuits are designed to perform logical operations, the way they perform these operations and the type of inputs they use differ greatly. In this article, we will explore the differences between combinational circuit and sequential circuit.
Combinational Circuit
A combinational circuit is a circuit that produces an output based solely on the input values provided at the time of the calculation. It is called “combinational” because the circuit combines the input information to produce an output. A combinational circuit does not require any memory and therefore does not take into account the previous state of the input. The output of a combinational circuit entirely depends upon the input values provided at the time of calculation.
Sequential Circuit
A sequential circuit is a circuit that uses its current input and also the past output/s to determine the current output. It is called “sequential” because the circuit takes into account the previous state or states of the input to calculate the current output. In contrast to a combinational circuit, a sequential circuit requires memory, in the form of flip-flops, to store the previous output/s or state.
Comparison
The primary difference between combinational circuit and sequential circuit is the way they store and use information. A combinational circuit does not store any information and solely depends on the input, whereas a sequential circuit stores information in flip-flops and makes use of past outputs to determine the current output. Another difference is that combinational circuits are simpler compared to sequential circuits as they only use simple logic gates such as AND, OR, and NOT gates. On the other hand, sequential circuits use combination of simple logic gates and flip-flops, which increases the complexity of the circuit.
Conclusion
In summary, the main difference between combinational circuit and sequential circuit is the way they store and use information to calculate the output. Combinational circuit solely relies on current input values, while sequential circuit depends on current input and past outputs. Both circuits are used in digital systems, but the sequential circuit provides more functionalities than combinational circuit due to its ability to store information.
Table difference between combinational circuit and sequential circuit
| Aspect | Combinational Circuit | Sequential Circuit |
|---|---|---|
| Definition | A combinational circuit is a digital circuit that produces an output solely based on the present value of the input signals, without considering any previous input values. | A sequential circuit is a digital circuit that produces an output based on the present input value and the previous input values that have been stored in memory elements. |
| Output | A combinational circuit produces an output based solely on the present input value. | A sequential circuit produces an output based on both the present input value and the previous input values stored in memory elements. |
| Memory elements | Combinational circuits do not contain any memory elements. | Sequential circuits contain memory elements such as flip-flops or registers. |
| Timing | Combinational circuits have no timing constraints since the output is solely dependent on the present input value. | Sequential circuits have timing constraints since the output is dependent on both the present and past input values which are dependent on the clock signal. |
| Design Complexity | Combinational circuits are simpler to design and analyze as they do not involve memory elements and timing constraints. | Sequential circuits are more complex to design and analyze as they involve memory elements and timing constraints. |