Sep 082014

What is a Combinational circuit?

combinational circuit is. as its name suggests, a circuit where the output depends only on the “combination” of the inputs at the time we are testing the output.

Analyzing the circuit made of digital gates shown below, the output of each depends only on their inputs. The output F will change if the input A or input B or both at the same time change. Combinational logic circuits are made of basic gates: AND gate, OR gate, NOT gate.

Combinational Circuit

They can also be built with NAND gates, NOR gates, XOR gates, which are a combination of the three basic gates. To understand a combinational logic circuit we can write its boolean equations and its truth table. The boolean equation of the above circuit is:


The truth table of the above circuit is:


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