The logic AND gate is one of the simplest gates in Digital Electronics.
The symbols for a 2 and a 3 input AND gates are shown in the following pictures.
The first one is the symbol of a 2 input AND gate and the second one is the symbol of a 3 input AND gate.
The 2 input logic AND gate is the most known, although it can have many more inputs (A, B, C, etc.), but it only has one output: X. The 2 input AND gate has the following truth table.
It is easy to see that the output X is "1" (logical 1, high level) when the input A and B are "1". In other words
The output X will be "1" when A and B inputs are "1"
The AND gate is represented by Boolean algebra as: X = A*B or X = AB.
A 3 input AND gate implemented with switches is shown in the following diagram.
The truth table is shown on the right side. Here O = Open and C = Closed
An AND gate may have many inputs. We can create a multiple input AND gate connecting 2 inputs AND gates in cascade.
The problem connecting AND gates in cascade is that the propagation time (time needed by the signal to travel from the input to the output) increases.
We can build a 3 inputs AND gate from 2 inputs AND gates in cascade as shown in the diagram below.
The truth table is similar to the one shown above, where switches are used.
In the same way we can implement a 4 or more inputs AND gates.
OR gate >>
