Combinational circuit

The combinational circuit consist of logic gates whose outputs at any time is determined directly from the present combination of input without any regard to the previous input. A combinational circuit performs a specific information processing operation fully specified logically by a set of Boolean functions. A combinatorial circuit is a generalized gate. In general such a circuit has m inputs and n outputs. Such a circuit can always be constructed as n separate combinatorial circuits, each with exactly one output. For that reason, some texts only discuss combinatorial circuits with exactly one output. In reality, however, some important sharing of intermediate signals may take place if the entire n-output circuit is constructed at once. Such sharing can significantly reduce the number of gates required to build the circuit. When we build a combinatorial circuit from some kind of specification, we always try to make it as good as possible. The only problem is that the definition of "as good as possible" may vary greatly. In some applications, we simply want to minimize the number of gates (or the number of transistors, really). In other, we might be interested in as short a delay (the time it takes a signal to traverse the circuit) as possible, or in as low power consumption as possible. In general, a mixture of such criteria must be applied.The combinational circuit consist of logic gates whose outputs at any time is determined directly from the present combination of input without any regard to the previous input. A combinational circuit performs a specific information processing operation fully specified logically by a set of Boolean functions. A combinatorial circuit is a generalized gate. In general such a circuit has m inputs and n outputs. Such a circuit can always be constructed as n separate combinatorial circuits, each with exactly one output. For that reason, some texts only discuss combinatorial circuits with exactly one output. In reality, however, some important sharing of intermediate signals may take place if the entire n-output circuit is constructed at once. Such sharing can significantly reduce the number of gates required to build the circuit. When we build a combinatorial circuit from some kind of specification, we always try to make it as good as possible. The only problem is that the definition of "as good as possible" may vary greatly. In some applications, we simply want to minimize the number of gates (or the number of transistors, really). In other, we might be interested in as short a delay (the time it takes a signal to traverse the circuit) as possible, or in as low power consumption as possible. In general, a mixture of such criteria must be applied.