2-12
Q10. Write the Boolean expression for an OR gate having G, K, and L as inputs.
Q11. How many input combinations are possible using G, K, and L?
Q12. How many of those combinations will produce a HIGH output?
THE INVERTER
The INVERTER, often referred to as a NOT gate, is a logic device that has an output opposite of the
input. It is sometimes called a NEGATOR. It may be used alone or in combination with other logic
devices to fulfill equipment requirements.
When an inverter is used alone, it is represented by the symbol shown in figure 2-9 (view A). It will
more often be seen in conjunction with the symbol for an amplifier (view B). Symbols for inverters used
in combination with other devices will be shown later in the chapter.
Figure 2-9. —Inverter: A. Symbol for inverter used alone; B. Symbol for an amplifier/inverter.
Let’s go back to the statement "Today is payday." We stated that P represents the TRUE state. If we
apply P to the input of the inverter as shown in figure 2-10, then the output will be the opposite of the
input. The output, in this case, is P . At times T0 through T2, P is LOW. Consequently, the output ( P ) is
HIGH. At T2, P goes HIGH and as a result P goes LOW. P remains LOW as long as P is HIGH and vice
versa. The Boolean expression for the output of this gate is f = P .
