The NOT Gate - Introduction & Design

 

The Inverter:

This performs the inverse operation of the buffer. It is also called the NOT gate. Output is the complement of the input. The inverter performs an inversion operation, changing one logic level to the other. 

Learning Objectives:

• Introducing AND gate implementation using

• Switches

• Diodes

• BJT

It has the same circuit symbol as that of a buffer except for the bubble present at the output side. This is the inversion bubble.

Logical Expression:

A = YC

The NOT
Input A	Output Y
0	1
1	0

Logical NOT Gate (Explain with the help of switches)

Look at the switch model, if the switch is closed (ON), the LED turns off. 

Similarly, if the switch is opened (OFF), the LED turns on. 

NOT Gate Using Universal Gates

Implementation Using Transistor Logic

When switch S1 is closed, the base-emitter junction is forward biased. Q1 is ON. No current flows from the LED. Similarly, when S1 is opened in the second case, the base-emitter junction is reversed biased. Q2 is OFF. LED turns ON in this case and hence the output is high. 

Implementation Using CMOS Logic