A combinational circuit is one where the output at any time is based only on the present combination of inputs at that point of time with complete dismiss to the previous state of the inputs. A combinational logic circuit has NAND, NOR, and NOT logic gates. These are the constructing blocks of digital circuitry. A combinational circuit supports a range of operations including the arithmetic operation of two operands, sharing of data, conversion of code, etc.
In these circuits, the output created at that time would base on the input of the specific time. There are three modifications of the combinational logic circuits such as the arithmetic and logical functions, data transmission, and code converters. The circuits involved in the arithmetic and logic circuits are the adders, subtractors, comparators, PLDs, etcetera.
A sequential circuit is a set of combinational circuits and memory components linked in the feedback path. The memory components are devices adequate for saving binary data within them. The binary data saved in the memory component at any given time represent the state of a sequential circuit. The sequential circuit gets binary data from external inputs. Therefore, a sequential circuit is determined by a time sequence of inputs, outputs, and internal gates.
Sequential circuits are the central unit of digital circuits. An example of a sequential circuit is the finite state machine. There are two types of Sequential Circuit, synchronous and Asynchronous Sequential circuit.
Synchronous Sequential Logic Circuit is the one in which the output is created with the input and the clock signal. A clock signal is given in a specific time interval. On the contrary, the asynchronous sequential logic circuit creates the response whenever there is a change in the input terminals.
Let us see the comparison between combinational circuit and sequential Circuit.
|Combinational Circuit||Sequential Circuit|
|Combinational circuits are not adequate for saving data (state). They do not include any memory component.||Sequential circuits have the memory area required for saving the current states sent as control inputs (enable) for the next set of operations. They include memory components that save data in digital circuits.|
|The combinational circuit is easy to design.||It is not easy to design a sequential circuit.|
|The current values of its outputs are resolved solely by the current values of its inputs.||The current values of its outputs are resolved by the current values of its inputs and its current state.|
|Combinational circuits are more costly.||Sequential circuits are inexpensive.|
|There is no condition for feedback.||Feedback is needed in this circuit.|
|An example of combination circuits is Parallel adder, Code converter, Decoder, etc.||An example of the sequential circuit is Serial Adder, Counter, shift register, etc.|
|The clock signal is not applied in the combinational circuit.||The clock signal is needed for sequential circuits.|