Difference Between Combinational and Sequential Circuit
Introduction
The main difference between a combinational and a sequential circuit is that a combinational circuit's output is only dependent on the input available at the time, but a sequential circuit's output is dependent on both the newest input and previous outputs. The sequential logic circuit has no feedback, but the combinational logic circuit has. As a result, the output created takes into account both current and previous outputs.
What is Combinational Circuit?
A combinational circuit is made up of a series of connected gates that provide output that is particular to the input at the time. The essential building elements of the combinational circuit are the basic AND, OR, and NOT or universal gates NAND and NOR. The output lines of the combinational circuit immediately follow the input lines, as indicated in the picture below. The decoder, which is used to convert binary code data into decimal code data, is a common example of a combinational circuit.
The output produced at that moment in these circuits would be determined by the input at that time. Combinational logic circuits come in three flavours: arithmetic and logical operations, data transfer, and code converters. Adders, subtractors, comparators, PLDs, and other circuits are included in the arithmetic and logic circuits. Multiplexers, demultiplexers, encoders, decoders, and other data transfer circuits are similar. The code converter circuits are BCD and 7 segments.
A combination circuit has n number of binary inputs and m number of binary outputs and is often used. It performs all of the essential operations of a digital computer.
What is a Sequential Circuit?
A sequential circuit is a kind of circuit in which the result is determined by both the current input and previous outputs. This circuit's unique feature is that the state of the output varies depending on the order in which the inputs are placed. This implies that the sequential circuits have enough memory to save the instantaneous findings.
It can, for example, remember whether logic level 0 or 1 is linked to its input and use that information at the output. The basic OR gate may be used to create this memory device.
Latches, flip-flops, and registers are examples of devices that implement sequential circuits. These inputs alternate between two states. There are two types of sequential circuits: synchronous and asynchronous circuits. When the internal state of the machine changes at a certain time set by a clock, the circuit is said to be synchronous.
Comparison Table Between Combinational and Sequential Circuits
| Combinational Circuits |
Sequential Circuits |
- There is no memory element in combinational circuits.
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- A memory element is present in sequential circuits.
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- Its outputs' current values are exclusively determined by the current values of its inputs.
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- The current values of its outputs are decided by its current state and the current values of its inputs.
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- The collection of output functions describes the behaviour of a combinational circuit.
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- The set of next-state functions and the set of output functions explain the behaviour of a sequential circuit.
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- Combinational circuits need more hardware to be realised.
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- The implementation of sequential circuits requires less hardware.
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- The truth table may be used to explain how it works.
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- A truth table and a timing diagram may be used to illustrate how it works.
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- The cost of a combinational circuit is higher.
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- Circuits that are built in a sequential order are less expensive.
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- The speed of a combinational circuit is faster.
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- The sequential circuit's speed is sluggish due to the memory components.
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Conclusion
The prior output is not required for the functioning of devices designed using a combinational circuit. The sequential circuit, on the other hand, requires the previous outputs to work and provide correct results.
