Two Input AND Gate

Here is an example of a two input gate as we have already seen. It is an AND gate and the truth table for this gate can be seen to the right of it.

Three Input AND Gate

Here is an example of a three input AND gate. Notice that the truth table for the three input gate is similar to the truth table for the two input gate. It works on the same principle, this time all three inputs need to be high (1) to get a high output.

Four Input AND Gate

Here is an example of a four input AND gate. It also works on the same principle, all four inputs need to be high (1) to get a high output. The same principles apply to 5, 6,..., n input gates.

Making Multi Input Gates

Multi input gates can be made by joining gates of the same type with less inputs. The diagrams below shows how a three input AND gate and and a four input AND gate can be made out of two input AND gates.

Exercise

See if you can work out how multiple input OR gates work by drawing truth tables for three and four input OR gates and then check with the answers.

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Richard Bigwood 2005