Unit-2
Difference between Combinational Circuits and Sequential Circuits
Combinational Circuits
In digital electronics, Combinational circuits are made up of logic gates.
Combinational circuits do not use memory storage element therefore output
of combinational circuit depends only on the present combination of inputs.
The output of each logic gate is determined by its logic function.
All the logic gates are used to build the combinational circuit but XOR and
XNOR gates are prominently used.
A combinational circuit is a kind of digital electronic circuit of which outputs
depend on the present inputs and have no connections to the past inputs. These
circuits do such tasks as additions, subtractions and logically AND, OR
and NOR circuits. The key characteristics of combinational circuits include:
No Memory Elements: The output is dependent solely on the current policy
inputs.
Immediate Response: Good input differs from its output and bad input
differs from its output.
Examples: The most commonly encountered examples are adders,
multiplexers and encoders.
,Example :
Half-Adder
Full Adder
Half Subtractor
Full Subtractor
Multiplexer
Demultiplexer
Encoder
Decoder
Advantages of Combinational Circuits
Simplicity: It is easier to design and implement, more so because it lacks
memory elements.
Speed: Operational at a faster rate as the output automatically adjusts with
the changes in inputs.
Resource Efficiency: Generally, it needs far fewer components as compared
to its equivalent sequential circuits.
Disadvantages of Combinational Circuits
Limited Functionality: Is not able to perform operations that need
historical information or sequence details.
Complexity with Increased Inputs: It becomes difficult to
design combinational circuits when there are many inputs.
, Sequential Circuits
A sequential circuit refers to a special type of circuit that consists of a
combinational circuit along with a clock and a memory element.
The output of a sequential circuit depends on a combination of both the
present inputs as well as the previous outputs. This previous output gets
treated in the form of the present state (current state).
Sequential circuits are quite different from combinational circuits in the sense
that they employ memory components. A sequential circuit provides output
based on current inputs as well as prior inputs; therefore, it is more functional.
Key features include:
Memory Elements: These circuits have a flip-flop or latch to store past
state information.
Time Dependency: Current input values as well as the previous input states
have an impact on the output.
Examples: Recurrent ones are counters and registers, while other formal
ones are finite state machines.
Examples :
1. Filp-Flop (Use to store 1 bit only)
2. Registers (Sequence of Filp-Flops)
Difference between Combinational Circuits and Sequential Circuits
Combinational Circuits
In digital electronics, Combinational circuits are made up of logic gates.
Combinational circuits do not use memory storage element therefore output
of combinational circuit depends only on the present combination of inputs.
The output of each logic gate is determined by its logic function.
All the logic gates are used to build the combinational circuit but XOR and
XNOR gates are prominently used.
A combinational circuit is a kind of digital electronic circuit of which outputs
depend on the present inputs and have no connections to the past inputs. These
circuits do such tasks as additions, subtractions and logically AND, OR
and NOR circuits. The key characteristics of combinational circuits include:
No Memory Elements: The output is dependent solely on the current policy
inputs.
Immediate Response: Good input differs from its output and bad input
differs from its output.
Examples: The most commonly encountered examples are adders,
multiplexers and encoders.
,Example :
Half-Adder
Full Adder
Half Subtractor
Full Subtractor
Multiplexer
Demultiplexer
Encoder
Decoder
Advantages of Combinational Circuits
Simplicity: It is easier to design and implement, more so because it lacks
memory elements.
Speed: Operational at a faster rate as the output automatically adjusts with
the changes in inputs.
Resource Efficiency: Generally, it needs far fewer components as compared
to its equivalent sequential circuits.
Disadvantages of Combinational Circuits
Limited Functionality: Is not able to perform operations that need
historical information or sequence details.
Complexity with Increased Inputs: It becomes difficult to
design combinational circuits when there are many inputs.
, Sequential Circuits
A sequential circuit refers to a special type of circuit that consists of a
combinational circuit along with a clock and a memory element.
The output of a sequential circuit depends on a combination of both the
present inputs as well as the previous outputs. This previous output gets
treated in the form of the present state (current state).
Sequential circuits are quite different from combinational circuits in the sense
that they employ memory components. A sequential circuit provides output
based on current inputs as well as prior inputs; therefore, it is more functional.
Key features include:
Memory Elements: These circuits have a flip-flop or latch to store past
state information.
Time Dependency: Current input values as well as the previous input states
have an impact on the output.
Examples: Recurrent ones are counters and registers, while other formal
ones are finite state machines.
Examples :
1. Filp-Flop (Use to store 1 bit only)
2. Registers (Sequence of Filp-Flops)
