In this lecture, we are going to learn about the Encoder in digital electronics, the types of encoders, and the application of encoders in digital electronics. We will also learn the detailed types of encoders. So let’s start with the basic knowledge of Encoder.
Encoder In Digital Electronics
An encoder is a combinational circuit that is designed to perform the inverse operation of the decoder.
An encoder has “n” number of input lines and “m” number of output lines.
An encoder produces an m-bit binary code corresponding to the digital input number.
The block diagram of the encoder is shown in the figure below.
The encoder accepts an n-input digital word and converts it into an m-bit another digital word.
The internal combinational circuit of the encoder is designed accordingly.
Also Read: Multiplexer in Digital Electronics
Types Of Encoder
The types of encoders that are going to be discussed in this lecture are as follows:
| Types Of Encoder | |
|---|---|
| 1. | Priority Encoder |
| 2. | Decimal to BCD Encoder |
| 3. | Octal to Binary Encoder |
| 4. | Hexadecimal to Binary Encoder |
Now we will discuss each encoder one by one.
Also Read: Demultiplexer in Digital Electronics
Priority Encoder
This is a special type of encoder.
Priorites are given the the input lines. If two or more input lines are logic-1 at the same time, then the input line with the highest priority will be considered.
Block Diagram of Priority Encoder
The block diagram of a priority encoder is shown in the figure below.
There are four inputs, D0 through D3, and two outputs Y1 and Y0. Out of four inputs, D3 has the highest priority and D0 has the lowest priority.
That means if D3 = 1 then Y1 Y0 = 11 irrespective of the other inputs. Similarly if D3 = 0 and D2 =1 then Y1 Y0 = 10 irrespective f the other inputs.
Priority Encoder Truth Table
Carefully go through the priority encoder truth table as shown in the below figure, to get the feel of the priority encode operation.
K-Maps for Priority Encoder Output
The K-maps for the two outputs of the priority encoder are shown in the below figure.
Priority Encoder Circuit
The logic diagram of the priority encoder or priority encoder circuit is shown in the below figure.
Priority Encoder in the IC Form
The priority encoders are available in the integrated circuit form. The available encoders are:
| 74147 IC | 10:4 Priority encoder |
| 74148 IC | Octal to binary priority encoder |
- The 74147 IC is basically a decimal to BCD priority encoder.
Also Read: Full Adder in Digital Electronics
Decimal To BCD Encoder
The block diagram of the Decimal to BCD encoder is shown in the below figure.
Decimal To BCD Encoder Truth Table
The truth table for a Decimal to BCD encoder is given in the below table.
Design of Decimal to BCD Encoder
- Consider output D from the above table. We observe that D = 1 only when the decimal input is 8 and 9.
- Therefore we can write that,
D = 8 + 9
- Similarly, the expression for the other outputs is,
C = 4 + 5 + 6 + 7
B = 2 + 3 + 6 + 7
A = 1 + 3 + 5 + 7 + 9
- The logic diagram of the Decimal to BCD encoder based on the above equations is shown in the figure below.
Also Read: Full Subtractor in Digital Electronics
Octal to Binary Encoder
The octal-to-binary encoder has 8 input lines and 3-output lines. Corresponding to the eight input octal numbers we get a three-bit binary output.
Note that in encoders only one input will have one value at a given time.
The block diagram of the octal-to-binary encoder is shown in the figure below.
Octal to Binary Encoder Truth Table
The truth table for the octal to Binary encoder is shown in the below table.
Logical Expression for Output of Octal to Binary Encoder
Referring to the truth table, we can write the logical expression for the outputs as follows:
B0 = D4 + D5 + D6 + D7
B1 = D2 + D3 + D6 + D7
B2 = D1 + D3 + D5 + D7
Implementation Using Basic Gates
The octal to binary encoder using the basic gates is shown in the below figure.
Also Read: Magnitude Comparator and Digital Comparator
Hexadecimal To Binary Encoder
The block diagram of the Hexadecimal to Binary encoder is shown in the figure below.
This encoder has 16 inputs “0 to F” and four binary outputs B3, B2, B1, and B0.
Hexadecimal To Binary Encoder Truth Table
The truth table of hex to binary encoder is shown in the below table.
In order to design the encoder, consider output B3. When the input is one of 8, 9, A, B, C, D, E, or F.
∴ B3 = 8 + 9 +A + B + C + D + E + F
Similarly, the expression for B2, B1 and B0 are as follows:
B2 = 4 + 5 + 6 + 7 + C + D + E + F
B1 = 2 + 3 + 6 + 7 + A + B + E + F
B0 = 1 + 3 + 5 + 7 + 9 + B + D + F
So the logic diagram of the Hex to Binary encoder is shown in the figure below.
Also Read: Classification of Logic Families |Characteristics of Logic Families
Application of Encoder in Digital Electronics
- Encoders serve as ubiquitous electronic circuits within the realm of digital systems.
- They find extensive utility in various applications, aiding in the translation of decimal values into binary representations. This translation facilitates the execution of fundamental binary operations like addition, subtraction, and multiplication.
- Furthermore, in specific instances, such as microprocessor applications, Priority Encoders prove invaluable for detecting interrupts.
Advantages of Encoders in Digital Logic
- Reduction in Line Complexity: One of the primary merits of employing encoders lies in their ability to streamline information transmission from multiple inputs to a single output. This reduction in line complexity simplifies system design and concurrently lowers component costs.
- Enhanced Reliability: By amalgamating multiple inputs into a solitary serial code, encoders contribute to heightened transmission reliability, minimizing the likelihood of errors in data transfer.
- Improved Performance: Encoders play a pivotal role in augmenting digital system performance by expediting the transmission of data from multiple inputs to a single output.
Disadvantages of Encoders in Digital Logic
- Increased Complexity: In comparison to multiplexers, encoders are generally more intricate circuits that necessitate additional components for implementation.
- Application Limitations: Encoders are exclusively suited for scenarios where a parallel set of inputs must be converted into a serial code, rendering them unsuitable for diverse applications.
- Limited Flexibility: Encoders exhibit limited flexibility, constrained to encoding a fixed number of inputs into a predefined number of outputs.
Also Read: Number System In Digital Electronics
FAQs on Encoder
What is an encoder in digital electronics?
An encoder is a combinational circuit that converts binary information in the form of 2N input lines into N output lines, which represent N bit code for the input.
Is an encoder input analog or digital?
Digital only
What is the principle used in the encoder?
The basic principle of an encoder is to assign a unique binary code to each possible input.
What is the difference between an encoder and a decoder?
The encoder encodes the actual data into binary code whereas the decoder decodes the encoded data, i.e., binary code to get the original data signal.
