Page 1075 - Basic Electrical Engineering

The number 85 is represented as 1010101.
Logic circuits or logic gates provide an output of logical 1 or logical 0 with
a certain logical input. The logic gates are classified into two categories viz

three logic gates and two universal gates. There are also two special types of
gates. These are shown below.

16.5.1 NOT Gate

A NOT gate works as an inverter. It has a single input and a single output.

The output signal is the negative of the input signal. The output is not the
same as input, the output negates the input. If input is A, the output is Ā (A-

bar).
Figure 16.1 shows a transistor circuit. When input A is 0 V, the transistor

is off because V = 0. The output voltage is the same as V , i.e., 5 V which
CC
BE
is referred to as 1. If input A is 1, i.e., 5 V, the transistor goes into saturation
and the output w ill be low which is referred to as 0. The logic symbol and
truth table for a NOT gate have also been shown in Fig. 16.1(b) and (c),

respectively.
Thus, the NOT gate is a logic gate that gives an output that is opposite to

the state of its input.