Experiment 25 - The 3-Input OR Gate with 2-Input OR Gates

With the OR logic you can combine 3 inputs. For this you can use 2 input OR gates...

Due to the associative law of the Boolean Algebra you are able to construct a 3-input OR gate using two 2-input OR gates.

The truth table remains unchanged...

A B C Q 0 0 0 0 0 0 1 1 0 1 0 1 0 1 1 1 1 0 0 1 1 0 1 1 1 1 0 1 1 1 1 1 Truth Table of the 3-input OR logic.

Logic diagram 3-input OR gate.

Circuit 3-input OR logic with 2-input OR gates. (Enlarge)

With two of the four OR gates on the C-MOS IC 4071 you can replicate the 3 input OR logic with the circuit shown.