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.

Figure 2-10. - Inverter input and resultant output.

You will recall that P is the complement of P.

The Truth Table for an inverter is shown below.

The output of an inverter will be the complement of the input. The following examples show various inputs to inverters and the resulting outputs:

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Q.13 What is the complement of XYZ?
Q.14

Q.15 In a properly functioning circuit, can both the input and output of an inverter be HIGH at the same time?