COMBINATIONAL CIRCUITS
• A combinational circuit consists of an interconnection of logic gates.
• Combinational logic gates react to the values of the signals at their inputs and
produce the value of the output signal, transforming binary information from the
given input data to a required output data.
• The n input binary variables come from an external source; the m output variables
are produced by the internal combinational logic circuit and go to an external
destination.
• In many applications, the source and destination are storage registers.
• If the registers are included with the combinational gates, then the total circuit must
be considered to be a sequential circuit.
• For n input variables, there are 2n possible combinations of the binary inputs.
• For each possible input combination, there is one possible value for each output
variable.
,BLOCK DIAGRAM
,Combinational Circuit vs Sequential
Circuit
Combinational Circuit Sequential Circuit
Present o/p is only depend on present i/p Present o/p depends on present i/p and previous
o/p
No Feedback Feedback
No Memory Memory
e.g. Half Adder (HA), FA, MUX, DEMUX e.g. Flipflop , Register, Counter
, ANALYSIS PROCEDURE
• The analysis of a combinational circuit requires that we determine the function that
the circuit implements.
• This task starts with a given logic diagram and culminates with a set of Boolean
functions, a truth table, or, possibly, an explanation of the circuit operation.
• The first step in the analysis is to make sure that the given circuit is combinational
• and not sequential.
• The diagram of a combinational circuit has logic gates with no feedback paths or
memory elements .
• Once the logic diagram is verified to be that of a combinational circuit, one can
proceed to obtain the output Boolean functions or the truth table
• A combinational circuit consists of an interconnection of logic gates.
• Combinational logic gates react to the values of the signals at their inputs and
produce the value of the output signal, transforming binary information from the
given input data to a required output data.
• The n input binary variables come from an external source; the m output variables
are produced by the internal combinational logic circuit and go to an external
destination.
• In many applications, the source and destination are storage registers.
• If the registers are included with the combinational gates, then the total circuit must
be considered to be a sequential circuit.
• For n input variables, there are 2n possible combinations of the binary inputs.
• For each possible input combination, there is one possible value for each output
variable.
,BLOCK DIAGRAM
,Combinational Circuit vs Sequential
Circuit
Combinational Circuit Sequential Circuit
Present o/p is only depend on present i/p Present o/p depends on present i/p and previous
o/p
No Feedback Feedback
No Memory Memory
e.g. Half Adder (HA), FA, MUX, DEMUX e.g. Flipflop , Register, Counter
, ANALYSIS PROCEDURE
• The analysis of a combinational circuit requires that we determine the function that
the circuit implements.
• This task starts with a given logic diagram and culminates with a set of Boolean
functions, a truth table, or, possibly, an explanation of the circuit operation.
• The first step in the analysis is to make sure that the given circuit is combinational
• and not sequential.
• The diagram of a combinational circuit has logic gates with no feedback paths or
memory elements .
• Once the logic diagram is verified to be that of a combinational circuit, one can
proceed to obtain the output Boolean functions or the truth table
