Theory - 51 :- Comparator - Encoders

Encoders

The combinational circuits that change the binary information into N output lines are known as Encoders. The binary information is passed in the form of 2^N input lines. The output lines define the N-bit code for the binary information. In simple words, the Encoder performs the reverse operation of the Decoder. At a time, only one input line is activated for simplicity. The produced N-bit output code is equivalent to the binary information

There are various types of encoders which are as follows:

4 to 2 line Encoder:

In 4 to 2 line encoder, there are total of four inputs, i.e., Y₀, Y₁, Y₂, and Y₃, and two outputs, i.e., A₀ and A₁. In 4-input lines, one input-line is set to true at a time to get the respective binary code in the output side. Below are the block diagram and the truth table of the 4 to 2 line encoder.

Block Diagram:                                                Truth Table:

The logical expression of the term A0 and A1 is as follows:

A₁=Y₃+Y₂
A₀=Y₃+Y₁

Logical circuit of the above expressions is given below:

8 to 3 line Encoder:

The 8 to 3 line Encoder is also known as Octal to Binary Encoder. In 8 to 3 line encoder, there is a total of eight inputs, i.e., Y₀, Y₁, Y₂, Y₃, Y₄, Y₅, Y₆, and Y₇ and three outputs, i.e., A₀, A1, and A₂. In 8-input lines, one input-line is set to true at a time to get the respective binary code in the output side. Below are the block diagram and the truth table of the 8 to 3 line encoder.

Block Diagram:                                    Truth Table:

The logical expression of the term A0, A1, and A2 are as follows:

A₂=Y₄+Y₅+Y₆+Y₇
A₁=Y₂+Y₃+Y₆+Y₇
A₀=Y₇+Y₅+Y₃+Y₁

Logical circuit of the above expressions is given below:

Decimal to BCD Encoder

The Octal to Binary Encoder is also known as 10 to 4 line Encoder. In 10 to 4 line encoder, there are total of ten inputs, i.e., Y₀, Y₁, Y₂, Y₃, Y₄, Y₅, Y₆, Y₇, Y₈, and Y₉ and four outputs, i.e., A₀, A1, A₂, and A₃. In 10-input lines, one input-line is set to true at a time to get the respective BCD code in the output side. The block diagram and the truth table of the decimal to BCD encoder are given below.

Block Diagram:                                          Truth Table:

The logical expression of the term A₀, A₁, A₂, and A₃ is as follows:

A3 = Y9 + Y8
A2 = Y7 + Y6 + Y5 +Y4      
A1 = Y7 + Y6 + Y3 +Y2      
A0 = Y9 + Y7 +Y5 +Y3 + Y1

Logical circuit of the above expressions is given below:

Uses of Encoders:

1. These systems are very easy to use in all digital systems.
2. Encoders are used to convert a decimal number into the binary number. The objective is to perform a binary operation such as addition, subtraction, multiplication, etc.