Introduction to Logic Gates
AND
Contents
As its name implies, an AND logic gate performs an “AND” logic operation, which is a multiplication. It has at least two inputs. So, if A and B are its inputs, at the output we will find A x B (also represented as A · B). So, AND logic gate can be summarized by the formula Y = A x B (or Y = A · B). You can see its symbol in Figure 3 and its truth table right below it.
Figure 3: AND logic gate.
| A | B | Y |
| 0 | 0 | 0 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 1 |
Another way to understand AND logic gate: its output will only be at “1” when all its inputs are also at “1”. Otherwise its output will be “0”.
If you are projecting a circuit and need an AND logic gate with more inputs, you can go ahead and simple draw an AND logic gate like the one in Figure 3 and put more inputs on it. But if you are working with integrated circuits with AND logic gates with fewer inputs that you need, you can expand the number of inputs by connecting them like shown in Figure 4.
Figure 4: Expanding AND inputs using 2-input gates.
The most famous AND gate integrated circuit is 7408 and you can its pinout in Figure 5. Of course there are several other integrated circuits that provide AND gates with more inputs. For example, 7411 provides three three-input AND gates.
Figure 5: 7408 integrated circuit provides four two-inputs AND gates.