Difference Between Encoder and Decoder

The fundamental difference between encoder and decoder lies in their operational direction: an encoder is a device that converts unambiguous (plain text) data into a coded format, whereas a decoder is a device that converts coded data back into its original state.

This article will explain what encoders and decoders are. We will also go through the differences that set them apart, even after both are combinational circuits. A combinational logic circuit is a circuit that contains different types of logic gates. There are n numbers of inputs, and m numbers of outputs are possible in a combinational logic circuit. 

Table of Content (TOC)

• Encoder and Decoder - Tabular Comparison
• What is an Encoder?
• How Encoder Works?
• What is a Decoder?
• How Decoder Works?
• Key Differences Between Encoder and Decoder

Encoder and Decoder - Tabular Comparison

Aspect	Encoder	Decoder
Function	Converts information signal to a coded digital bitstream.	Converts coded bits back to the original information signal.
Input Lines	2^n input lines.	n input lines.
Output Lines	n output lines.	2^n output lines.
Operation Complexity	Relatively simple operation.	More complex operation compared to encoders.
Basic Logic Element	Primarily uses OR gates.	Utilizes AND gates along with NOT gates.
Installation Location	Installed at the transmitting end.	Installed at the receiving side.
Applications	Commonly used in video encoding, emails, etc.	Frequently used in memory chips, microprocessors, etc.
Example of Operation	Converts raw signals to coded signals.	Converts coded signals back to their original or raw form.
Nature of Output	Produces coded outputs.	Produces active/raw/original outputs.

What is an Encoder?

An encoder is a device or combinational circuit that converts an active data signal into a coded message format. It typically transforms analogue signals into digital signals.

In terms of binary information, it takes 2^n input lines and converts them into N output lines, representing an N-bit code for the input. The basic logic element that is used in encoders is the OR gate. Encoders are commonly used in videos, emails, etc.

How Encoder Works?

To understand how the encoder works, let's go through an example. 

Imagine an encoder with 8 inputs, which we can label as 00, 01, 02, 03, 04, 05, 06, and 07. According to the principle of '2^n inputs to n outputs', with 8 inputs (where 8 is 2^3), this encoder will produce 3 outputs (3-bit binary code). 

Inputs	Output
00	000
01	001
02	010
03	011
04	100
05	101
06	110
07	111

Each input (00 to 07) corresponds to a unique output code in the above table. For example, if 00 is active, the output is 000; if 01 is active, the output is 001, and so on.

What is a Decoder?

A decoder is a device or combinational circuit that is designed to do the reverse operation of the encoder. A decoder takes a coded input signal and converts it back into the original signal as output. 

It converts N lines of input into 2^N lines of output in binary terms. The decoder's role is to decode or convert coded information to its original, unambiguous form.

How Decoder Works?

Suppose we have a 3-bit binary input with 8 possible combinations (since 2^3 = 8). Each combination of these 3 bits corresponds to one of the 8 outputs.

3-bit Input (Combination)	Activated Output
000	00
001	01
010	02
011	03
100	04
101	05
110	06
111	07

If the 3-bit input is 010, then output 02 is activated. If the input is 111, then output 07 is activated, and so on.

Key Differences Between Encoder and Decoder

• An encoder converts information signals into a coded digital bitstream, whereas a decoder converts coded bits back into the original information signal.
• Decoder typically has a more complex operation due to the need to interpret the coding format. In contrast, an encoder has a more straightforward operation as it only needs to convert signals into a coded format.
• An encoder uses OR gates as the basic logic element, whereas a decoder uses AND and NOT gates.
• A decoder is installed at the receiving end to interpret coded signals. In contrast, an encoder is installed at the transmitting end to code the signals.
• The encoder accepts 2^n input lines and produces n output lines, whereas the decoder accepts n input lines and produces 2^n output lines.
• Decoder is commonly used in memory chips and microprocessors. On the other hand, an encoder is used in applications like video encoding and emails.
• An encoder produces coded outputs from the input signals, whereas a decoder produces active, raw, or original outputs from coded inputs.
• The decoder has a more complex internal logic circuitry to recover the original signal accurately. In contrast, an encoder typically has simpler circuitry, as it only needs to code the input signals into a binary format.

Conclusion

The primary difference between encoder and decoder is that the binary information is passed in 2n input lines, changing the input into n output lines. Meanwhile, in a decoder, the binary information is passed into n input lines, which are changed into 2n output lines.