Difference Between Encoder And Decoder On Your Fingertips!

11 mins read

Data is constantly being transformed and transmitted in the digital world. Encoders and decoders play a crucial role in this process. These electronic circuits act like translators, converting data from one format to another. But it’s important to know the difference between encoder and decoder.

Before we dive into these differences, let’s understand the meaning of a combinational circuit. Why? Because encoder and decoder are combinational logic circuits.

What are Combinational Circuits?

A combinational circuit consists of an interconnection of logic gates, the outputs of which are decided only by the current combination of inputs at any given time. Unlike sequential circuits, combinational circuits do not have memory or feedback loops, meaning their outputs are purely a function of the present inputs without regard to previous input states.

Below is a block diagram of a combinational circuit. The n input binary variables come from external sources. The internal combinational logic circuit generates the 'm' output variables, which are sent to an external destination.

Each input and output variable exists physically as an analog signal whose values are binary signals representing logic "1" and logic "0."

Note that a combinational circuit can also be specified by a truth table that lists the output for each combination of input variables.

Now, let's discuss the difference between encoder and decoder.

Difference Between Encoder And Decoder: An Overview

Encoder:

• Function: Converts data from one format to another, typically compressing or transforming it for efficient transmission or storage.
• Example: A text encoder converts human-readable text into a machine-readable format like ASCII or UTF-8.

Decoder:

• Function: Reverses the process of encoding, converting data back to its original format.
• Example: A text decoder converts an ASCII-encoded message back into human-readable text.

Key Difference Between Encoder and Decoder:

In essence: Encoders and decoders work together to ensure data is transmitted or stored efficiently and can be accurately retrieved.

What is Decoder?

A decoder is a combinational logic circuit that converts binary data or binary code from ‘n’ bit input lines to a maximum '2n’ unique output line such that only one output line is stimulated for each one of potential combinations of input.

A decoder has many inputs and outputs and accepts binary code as input. Also known as selectors, decoders are widely utilized in computer memory systems.

Decoders are used to convert or to identify a particular code, for example:

1. Binary to Octal (3 to 8-line decoders)
2. Binary to Hexadecimal (4 to 16 line decoders)
3. BCD to Decimal (4 to 10 line decoders)
4. BCD to 7 - segment display.
5. BCD to 3 - segment display
6. BCD to 2 - segment display
7. BCD to 1 - segment display
8. BCD to 0 - segment display
9. BCD to Dot Matrix Display
10. BCD to Liquid Crystal Display

BCD stands for Binary Coded Decimal. It is another method for converting decimal values to binary equivalents.

If the n-bit decoded information has unused or doesn’t care combinations, the decoder output will have less than 2n outputs.

If n = total number of input lines
m = a total number of output lines.
then m <= 2n.

Following is a general block diagram of a decoder:

BCD to 7 - segment display decoder

One of the most popular and simplest methods for displaying numerical digits is a "7-segment display” to form the decimal characters '0' through '9' and sometimes the HEX characters' A' through 'F'. It is used in electronic calculators, digital multimeters, watches, etc. 

This decoder takes a 4-bit BCD input and generates outputs that carry current through the correct segments to display the decimal digit.

The figure below shows a seven-segment display consisting of seven light-emitting segments.

Note:

1. The internal circuitry of the decoder and Demultiplexer is exactly the same.
2. A decoder with enabled signal input can function as a demultiplexer.
3. A 2 X 4 line decoder may act like a 1: 4 Demultiplexer and vice-versa.
4. The basic logic element in the decoder contains AND gates or NAND gates.

What is an Encoder?

An encoder is a combinational circuit that carries out the inverse operation of a decoder. It is a device that converts analog signals into digital signals.

It has 2n input lines and ‘n’ output lines. Only one of the 2n input lines is activated at a given time. Depending on which input is activated, it produces an n-bit output code. Like the decoder, the encoder has no selection lines.

The below figure shows the general block diagram of an encoder with m number of inputs and n-number of outputs, where, m=2n or n = log2m. 

The encoder is used to convert other codes to binary, such as,

1. Octal-To-Binary encoder (8 X 3 line)
2. Decimal to BCD encoder (10 X 4 line)
3. Hexadecimal-To-Binary encoder (16 X 4 line)
4. Decimal-to-Binary encoder

Note: The basic logic element in the encoder contains OR gates.

What are the types of encoders?

1. Priority Encoder

The encoders discussed above will work properly as long as one and only one decimal input is 'high' at any given time.

However, in some practical systems, two or more decimal inputs may simultaneously become 'high'. To remove this disadvantage, a modified version of the simple encoder is used - the "priority encoder".

A priority encoder is a logical circuit comprising priority functions to ensure that when two or more inputs are equal to '1' or high simultaneously, the input having the highest priority will take precedence.

Following is a block diagram of a priority encoder.

2. Four Input Priority Encoder

The truth table of a 4-bit priority encoder is described below. The inputs are called I0, I1, I2, and I3, in addition to the two outputs, Y1 and Y0.

The circuit has a third output called X, activated when one or several inputs are 'high'. If all the inputs are '0' or 'low', there are n valid inputs, and X = 0. The following is a truth table of a four-input priority encoder.

Based on the truth table shown, the higher the subscript numbers, the higher the priority of the input. Input I3 has the highest priority. Whatever the other input values are, when the input is high, the output for Y1 Y0 = 11.

Now I2 has the next priority thus when I3 = 0 and I2= 1 whatever other lower priority inputs are shown as don't care the outputs Y1 Y0 = 10.

Similarly, for I1, I2 and I3 must be 'low', and I0 is don't care, with outputs Y1 Y0 = 01. For I0 (lowest priority), all the other inputs are 'low', and output Y1 Y0 = 00.

Difference between Encoder and Decoder

Applications of Encoders and Decoders

Encoders and decoders are widely used in various fields of electronics, telecommunications, and computing. Here are some key applications:

Applications of Encoders:

1. Digital Communication Systems: Encoders are used to convert data into a format suitable for transmission, such as encoding digital signals for efficient transmission over communication channels.
2. Robotics and Automation: In robotics, encoders are used to convert motion into a coded signal, which can then be used to determine position, speed, or direction of motors and other components.
3. Memory Addressing: Encoders are employed in memory devices to select a specific memory address from a large set, allowing access to particular data stored in memory.
4. Sensor Systems: Encoders are used in sensors to convert physical measurements, like angular or linear position, into digital signals for further processing.
5. Input Devices: In devices like keyboards, encoders convert key presses into binary code that computers can process.

Applications of Decoders:

1. Digital Displays: Decoders are used to convert binary or other coded data into a form that can be displayed, such as converting binary input to drive a seven-segment display.
2. Communication Systems: Decoders are essential in digital communication to decode the received encoded signals back into their original form, such as in satellite TV receivers or data packet decoders in networking.
3. Data Retrieval: In memory systems, decoders are used to select the correct data line from the memory address during the read operation.
4. Signal Processing: Decoders are used in signal processing to convert coded inputs, such as DTMF signals in telephony, into a form that can be used to perform specific functions.
5. Automated Control Systems: Decoders are employed to interpret coded control signals in automation systems, enabling the control of various devices like motors, lights, and machinery.

Both encoders and decoders play critical roles in enabling efficient data processing, transmission, and control across a wide range of applications.

Final Remarks

To conclude, both encoder and decoder are combinational logic circuits, but they complement each other in their operations. The first encodes the actual data signal, while the second decodes the coded data bits to obtain the exact message signal. There are numerous other uses for encoders and decoders.

Frequently Asked Questions

1. Define a digital circuit.

An electrical circuit that uses digital signals to function is referred to as a digital circuit. Digital signals can have one of two discrete levels: ON/OFF, 0/1, or True/False. Boolean logic's principles, which include logical operations like AND, OR, and NOT, are used to handle binary data in this system.

2. Mention some applications of an encoder.

Some applications of an encoder are:

• Automatic health monitoring systems
• RF-based home automation system
• Robotics vehicle with a metal detector
• War field flying robot with a using night-vision flying camera
• Speed synchronization of multiple motors in industries
• Encoder for CNC machines

3. What is the function of a decoder?

A decoder is a circuit that translates a coded input signal into its original form or expresses the meaning of the input binary code through output signals. It performs the reverse operation of an encoder and is used in various applications such as memory addressing device selection, and signal decoding.

4. Give an example of a decoder.

A line decoder is an example of a decoder. A line decoder is a typical sort of decoder that converts an input n-digit binary integer into 2n data lines. The 1-to-2 line decoder, which contains the following truth table, is the simplest type of line decoder:

This means that when the input A is 0, the output D1 is 0 and D0 is 1. When the input A is 1, the output D1 is 1 and D0 is 0.

5. What is a video encoder?

A tool or piece of software known as a video encoder transforms video signals from one format to another. It uses a variety of methods and approaches to encode an input video stream—typically in a raw or uncompressed format—into a compressed version. A video encoder's primary function is to compress video data while retaining acceptable levels of quality. For effective video material storage, transport, and streaming, this compression is essential.

6. Name the different kinds of encoding available.

The three main kinds of encoding are visual, acoustic, and semantic.

And that is all on this topic. For more useful content, stay tuned to Unstop!

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