Page 27 - DCAP108_DIGITAL_CIRCUITS_AND_LOGIC_DESIGNS

Digital Circuits and Logic Design

Notes 2.1.2 The AND Gate
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 * B (also represented as A • B). So, AND logic gate can be summarized by the formula
Y = A* B (or Y = A * B).
Figure 2.3: AND Logic Gate

Table 2.2: Truth Table

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 2.3 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 2.4.

Figure 2.4: Expanding AND Inputs Using 2-Input Gates

The most famous AND gate integrated circuit is 7408 and you can its pinout in Figure 2.5. 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 2.5: 7408 Integrated Circuit Provides Four Two-Inputs AND Gates

22 LOVELY PROFESSIONAL UNIVERSITY