2-14
Q13. What is the complement of XYZ?
Q14. The input to an inverter is X + (YZ). What is the output
Q15. In a properly functioning circuit, can both the input and output of an inverter be HIGH at the
same time?
THE NAND GATE
The NAND gate is another logic device commonly found in digital equipment. This gate is simply an
AND gate with an inverter (NOT gate) at the output.
LOGIC SYMBOL
The logic symbol for the NAND gate is shown in figure 2-11.
Figure 2-11. —NAND gate.
The NAND gate can have two or more inputs. The output will be LOW only when all the inputs are
HIGH. Conversely, the output will be HIGH when any or all of the inputs are LOW.
The NAND gate performs two functions, AND and NOT. Separating the NAND symbol to show
these two functions would reveal the equivalent circuits depicted in figure 2-12. This should help you
better understand how the NAND gate functions.
Figure 2-12. —NAND gate equivalent circuit: A. Either X or Y or both are LOW; B. Both X and Y are HIGH.
