Key Takeaways:
- Encoders are used to turn multiple inputs into a smaller binary output, reducing the number of wires needed by representing inputs with coded values.
- They help simplify digital systems by converting button presses or signals into binary codes, making circuits cleaner and more organized.
- In a basic encoder, only one input should be active at a time—multiple active inputs can lead to incorrect results.
- Priority encoders address this issue by assigning precedence to inputs, ensuring accurate output even when multiple inputs are active.
- Common encoder types include 4-to-2, 8-to-3, and decimal-to-BCD, each designed for specific input-output combinations.
- Encoders are built using simple logic gates like OR gates, making them easy to implement in digital circuit designs.
- They reduce wiring complexity—for example, encoding 8 buttons into just 3 output lines instead of using 8 separate wires.
- Encoders are used in everyday applications like keyboards, CNC machines, communication devices, and medical systems.
In digital electronics, an encoder is a type of logic circuit used to convert information from one format to another — specifically, it takes multiple input signals and converts them into a smaller number of binary output bits. It may sound simple, but this small component plays a big role in how digital systems manage data efficiently.
Let’s say you have several input lines, but at any given moment, only one of them is active (HIGH). An encoder looks at which input is active and then generates a binary code that represents its position. This is why it’s called an encoder — it’s literally encoding positions or signals into binary values.
In this blog, we’ll walk through what an encoder is, how it works, the types of encoders you’ll come across, how to build its logic circuit, and where it’s commonly used in the real world.
Table of Contents:
What Is Encoder in Digital Electronics?
“A Binary Encoder is the combinational circuit that has n outputs and 2 to the power n or fewer inputs.”
In the encoder, it has been assumed that at any given time, only one of the inputs is HIGH. And depending on which input is HIGH, we get the specific code at the output.
Key Functions of an Encoder
One of the main purposes of using an encoder is to convert input signals into a coded format. Typically, the input is in the form of multiple active signals, and the encoder takes these and converts them into a smaller set of binary codes. For example, if you have 8 input lines, the encoder will convert the active line into a 3-bit binary code. This helps in identifying which input is active, using fewer bits for processing.
For example: Imagine if you had a calculator keypad. The thing is that when you press a number, say ‘7’, there is a circuit that detects which key was pressed and converts it to a binary value which would be 0111. The number is then used by the processor to be displayed, or to be calculated.
This simplifies the wiring to the inside and helps the microcontroller figure out which key was pressed without requiring a wire for every key.
2. Parallel to Serial Conversion
Encoders are also useful in converting data from a parallel format to a serial format. In most systems presented, data is processed in parallel form for powerful raw processing, and they must be accessed over a communication line or stored efficiently; as they need to be converted into a serial form. This conversion is the main purpose of the encoder due to which the information can be transmitted bit by bit, however, the initial input is always preserved.
Example: USB keyboards. Within the keyboard, the keypresses are stored in registers in digital electronics following a matrix method (parallel form), however it is sent serially, over the USB cable, to the computer. The encoder assists in converting such parallel key data into serial format on bit by bit basis to make them compatible with communication standards.
3. Reducing Wiring Complexity
And then when you have to work with multiple inputs and only so many lines to transport that data, things can get very messy in terms of wiring. An encoder can simplify this to some extent. The advantage is that instead of sending over individual wires for each input (as positive logic requires), you just send over the coded binary output. This has the advantage of requiring less switching lines and less complexity in its circuit. It is particularly beneficial in big digital systems, where space and efficiency are important.
Example: There are multiple buttons or control signals in industrial machines. Rather than running 16 wires to a controller between buttons, we can actually convert which button is pressed to a 4 bit binary value using an encoder. All of these 4 bits are transmitted on only 4 lines. This simplifies the system and makes it easier to debug.
Types of Encoders
There are following types of Encoders,
1. 4 to 2 Bit Encoder
Let’s take the case of a 4-line to 2-line encoder, and let’s understand the working of this encoder.
So as you can see, this 4-line to 2-line encoder has 4 inputs and 2 outputs. That means here at the output, this n is equal to 2. And the total number of inputs is equal to 2 to the power n, that is equal to 4. And here is the truth table of this 4-to-2 encoder.
When the D0 input is HIGH, then the output of the encoder is equal to 0,0. Likewise, when this D1 input is HIGH, then the output of the encoder is equal to 0, 1. Similarly, when the D2 is HIGH, then the output will be equal to 1, 0.
When D3 is HIGH, then the output of the encoder will be equal to 1, 1. So in this way, this binary encoder encodes the input information into the compact binary code. So now, let’s see the logic circuit of this 4-line to 2-line encoder.
From this truth table, the output A is HIGH when either D2 is HIGH or D3 is HIGH. That means the logical expression of this output A is equal to D2 + D3. Likewise, this output B will be HIGH when either D1 is HIGH or D3 is HIGH.
That means the logical expression of this output B is equal to D1 + D3. And these two logical expressions can be implemented with the help of OR gates. So this is the logic circuit of this 4-line to 2-line encoder.
Similarly, now let’s see the 8-line to 3-line encoder.
2. 8 to 3 Bit Encoder or Octal to Binary Encoder
So in case of this 8 to 3 bit encoder, it has 8 inputs and 3 outputs. And depending on which particular input is HIGH, we get the specific 3-bit code at the output.
Here is the truth table of this 8-line to 3-line encoder.
When this D0 input is HIGH, then the corresponding output code is equal to 0, 0, 0. Likewise, when the D5 input is HIGH, then the output code is equal to 1, 0, 1.
Similarly, when this D7 is HIGH, then the corresponding output code is equal to 1,1,1. So in this way, we get the specific output code corresponding to the individual inputs. And based on this truth table, we can also design the logic circuit of this 8 to 3 encoder.
This output A is HIGH, when either D4 is HIGH or D5 is HIGH or D6 is HIGH or D7 is HIGH. So we can say that this logical expression of this A is equal to D4 plus D5 plus D6 plus D7. Likewise, this B is HIGH, when either D2 or D3 is HIGH or this D6 or D7 is HIGH.
i.e. the logical expression of this B is equal to D2 plus D3 plus D6 plus D7. Similarly, this C output is HIGH, when either D1 is HIGH or D3 is HIGH or D5 is HIGH or D7 is HIGH. So we can say that the logical expression of this C is equal to D1 plus D3 plus D5 plus D7.
So, in this way, we got the three logical expressions for the outputs A, B and C. These three expressions can be implemented with the help of OR gates. So this is the logic circuit of this 8-line to 3-line encoder. So as you can see, this binary encoder encodes the input information into the compact code.
So in this way, the encoder is particularly useful when we want to connect so, many input devices to the processor or the controller. For example, let’s say we want to connect the 8 switches to the controller. Let’s say each key represents a specific symbol or a specific action.
For example, we are designing a gaming pad for some application. That means whenever this key is pressed, then the input to the particular pin is equal to Vcc. And in that case, we will get the high input at the particular pin.
When the switch is not pressed, then the input to that pin is equal to zero. So in this way, the processor or the controller can know that the particular key is pressed. Therefore, without an encoder, in this case, we require the 8 such input-output pins of the controller.
Of course, nowadays, the controller comes with so many IO pins. But when you want to connect so many inputs to the controller, then you might run out of the number of IO pins. So in such cases, the encoder is very useful.
So in such a case, what we can do, we can connect the 8 switches to the encoder. And the output of the encoder can be given to the controller. So depending on which key is pressed, we get the specific code at the output of the encoder.
By reading that code, the controller can know that which key is pressed. So in this case, instead of the 8 pins, we just require the 3 pins. And in this way, we can save the number of IO pins.
So that is one of the uses of this binary encoder. So this 8-line to 3-line encoder, which we have discussed, can also be used for octal to binary conversion. So in such case, each input represents the specific octal number, and the output of the encoder is the binary code, which is equivalent to the particular octal digit.
So likewise, we can also design the decimal to BCD encoder.
3. Decimal to BCD Encoder
Decimal to BCD encoder, we have 10 inputs and 4 outputs. So here, each input represents a specific decimal digit, and the output is the BCD equivalent code corresponding to the particular digit.
So here is the truth table of this Decimal-to-BCD encoder.
Corresponding to the particular input, we get the 4-digit BCD code. That means whenever this D0 input is high, then the corresponding BCD code is equal to 0000.
Likewise, when this D7 input is high, then the corresponding BCD code is equal to 0111. And similarly, when this D9 input is high, then the corresponding BCD code is equal to 1001. So with the help of the truth table, we can also design the logic circuit of this encoder.
For example, this output A is high when either D8 is high or D9 is high. That means the logical expression of this A is equal to D8 plus D9. Likewise, this B output is high when this D4 is high or D5 is high or D6 is high or D7 is high.
That means the logical expression of B is equal to D4 plus D5 plus D6 plus D7. Similarly, the output C is high when either D2 is high or D3 is high. Likewise, this output C is also high when this D6 is high or D7 is high.
So, we can say that this logical expression of C is equal to D2 plus D3 plus D6 plus D7. Likewise, the logical expression of D is equal to D1 plus D3 plus D5 plus D7 plus D9. So this is the logical expression of D. So in this way, we got the four different expressions for the individual outputs.
And each of them can be implemented with the help of OR gates. So, here is the OR logic circuit of this decimal to BCD encoder.
And in this way, we can implement the particular encoder.
4. Limitations of Encoders and Need for Priority Encoders
So now, let’s see few limitations of this normal encoder. So in case of the normal encoder, we have assumed that at the most only one input is high. But when all the inputs of the encoder are zero or when more than one input is high, then this encoder circuit will not work properly.
And to understand that, let’s take the case of this 8-line to 3-line encoder. So in case of this 8 to 3 encoder, when this D0 input is high, then the corresponding output is equal to 000. And that is also evident from the logic circuit.
Because here, this D0 input is not connected to any of the OR gates. That means whenever this D0 input is high and all other inputs are zero, then the output of the three OR gates will be equal to 000. But suppose if all the inputs are zero, then also the output of this encoder will be equal to 000.
That means for the two different input conditions, we will get the same output. So, to resolve this discrepancy, we can have one more output to this encoder. Which will indicate that at least one of the inputs to the encoder is high.
So if all the inputs to the encoder are zero, in that case, this output V will also be equal to zero. And when this V is equal to zero, in that case, it doesn’t matter what the other output of this encoder is. So in this way, we can distinguish the condition when all the inputs to the encoder are zero.
Apart from that, the other issue with this encoder is that if more than one input is high, then the output of the encoder will be invalid. For example, if this D1 input is high, then the output of this third OR gate will become high. And if rest of the inputs to the encoder are zero, in that case, the output of these OR gates should be equal to 001.
Similarly, when this D2 input is high, then the output of this second OR gate will become high. And if the remaining inputs are zero, then in that case, the output of this encoder will be equal to 010. But suppose, if both inputs D1 and D2 are high simultaneously, in that case, the output of this second and third OR gate will become high.
And if we see the overall output of this encoder, then that is equal to 011. And this output indicates D3 is HIGH, but actually, both D1 and D2 are HIGH.
And in this condition, we are getting the invalid result. That means this normal encoder will not work when more than one input to the encoder will be high. And to avoid that, we need to set the priority to the inputs. Now, you might be wondering “what is priority encoder in digital electronics?”
What Is Priority Encoder in Digital Electronics?
“A priority encoder in digital electronics is a combinational circuit that assigns a binary code to the highest-priority active input among multiple inputs. It ensures that when multiple inputs are high, only the one with the highest priority is encoded.”
For example, we can set the priority so that when more than one input is high, then the input with the higher subscript will have more priority.
And in that case, that input will be considered as high. So such encoders are known as the priority encoder.
So let’s say, in this priority encoder, the input with the higher subscript has the higher priority. So now, suppose this D1 and D2 inputs are high simultaneously; in that case, D2 will have more priority. And in that case, the output of the encoder will be equal to 010.
On the other hand, if D2 and D5 are high simultaneously, in that case, D5 will have more priority. And in that case, the output of the encoder will be equal to 101. So in this way, in the case of the priority encoder, even if more than one input is high, then based on the priority, we will get the specific code at the output.
So apart from that, to detect the all-zero input condition, we can also have one more output to this priority encoder. That means when all the inputs are 0, then this output V will also be equal to 0. While, when one or more than one, input is high, then this output V will be equal to high. So in this way, with the help of the priority encoder, we can eliminate the two limitations of this normal encoder.
Advantages of Encoders
- Data compression: Compression allows encoders to use less number of bits for the representation of information.
- Efficient Data Transmission: Encoded data can be transmitted over communication channels more efficiently.
- Error Detection and Correction: Special encoders to detect and correct errors in digital data.
- Standardization: To simplify calculations, encoders may standardize data.
Disadvantages of Encoders
- Increased Complexity: Encoders can introduce further complexity to digital systems by requiring additional hardware or software. This is applicable for complex or custom encoders.
- Loss of data: If the encoders are not constructed right, they may lose data in the process of encoding.
- Propagation Error: Misinformation can propagate in the system.
- Decoding: The original information must be restored from the encoded data, i.e., decoding or reverse coding is required, which adds an extra step.
Applications of Encoders
Encoders in digital electronics can be thought of as small devices in the digital system; however, they are used in a wide range of applications such as medical applications, manufacturing machinery, automotive, and more. From computers to medical equipment, they silently undertake the task of turning signals, positions, or actions into digital code that other systems can interpret and act on.
Consider a few examples from the real world! Such as:
1. In Computer Systems
Encoders in digital electronics are commonly employed in microprocessors and controllers. As is the case with receiving more than one signal (such as having a printer ready for a new job to print or a user clicking a mouse), priority encoders can be used to determine which one we should respond to first. They can also be used to minimize the size of control words in microprogramming by encoding larger sets of control inputs into smaller, more compact binary codes.
2. Motor Speed Synchronization
In a lot of work settings, however, more than one motor needs to be synchronized to work together, think conveyor belts and robotic arms, and encoders assist in keeping their speeds in sync. Even if one motor starts to stall, the system slows one or more others accordingly, so things continue to move smoothly and in sync.
3. CNC Machines
In CNC machines, such as drilling, mining, and shaping machines, encoders assist in controlling the precise movement and position of tools. They make sure every action is precise (which is important when you’re cutting or shaping materials with precision).
4. Electronics Industry
The electronics industry uses encoders in processes such as chip making. Different kinds are employed depending on the task, which may include rotary encoders, angle encoders, and linear encoders, all to measure and gauge the motion, position, and speed in sensitive machinery.
5. Medical Equipment
Rotary encoders are crucial to ensure part positioning in machines such as CT scanners and MRI systems according to some specific safety criteria. Scans can be thrown off by even slight errors of positioning, and encoders help keep scans precise.
6. Data Routing in Communication
Encoders in digital electronics may be useful in communication systems for transmitting data efficiently. They condense or reformat data so it can travel through networks efficiently with relatively narrow pipes and be decoded faithfully at the other end. Or compare it to packing luggage efficiently for a flight and then unpacking after you arrive at your hotel.
7. Signal Processing
In signal processing, encoders can convert symbolic or categorical data (not analog signals) into digital format for compression or transmission. This makes them faster to store, read, or send. They can also be used to measure things like angles or distances and even to count how many times an event occurs, like a gear turning or a signal pulsing.
8. Address Encoding
They are used for efficient shifting of the converted address from character to BCD (Binary Coded Decimal) format. It is a handy thing in computer networks and communication systems, a way to make sure that data can be correctly transmitted and the system knows where to send or store the data.
9. Keyboards
When you strike your keyboard a micro-controller deciphers which key was struck by row and column. It turns that position into a BCD code and sends it to your computer, which then prints that character on the screen.
10. Positional Encoding
This is useful for determining where something is located, especially when it’s spinning, which is what you get when you have a shaft on a motor. In AI models such as transformers (a type of AI model used in natural language processing), positional encoding is crucial for the system to figure out how to use order of words (or tokens) in a sentence.
11. Handling Interrupt Requests
Encoders in digital electronics help work out who gets to the processor’s ear when multiple devices are vying for its attention at once. They not only create a schedule, but also regulate distractions and interruptions so that things get done and don’t overload.
Final Thoughts
Encoders in digital electronics might seem like a small part of a circuit, but they make a big difference in how digital systems stay organized and efficient. Whether it’s helping a keyboard talk to your computer or keeping motors in sync on a factory floor, they quietly do their job in the background. Learning how encoders work gives you a better grip on real-world electronics. They may not stand out, but they definitely keep things running smoothly.
Encoder in Digital Electronics – FAQ
1. What is the difference between an encoder and a multiplexer?
An encoder in digital electronics is serving multiple inputs and gives a binary output depending on which input is active. A multiplexer in digital electronics, however, chooses one of a number of input lines for output to a single output line under the control of control signals. So, then, though they both handle multiple signals, an encoder translates a number of positions mentioned into ‘binary codes’, while a multiplexer selects which input to allow through.
2. Can two inputs be active in a priority encoder?
Yes, but only slam that has the highest priority will be used. That’s the beauty of a priority encoder- it takes care of the multiple active inputs by having a defined priority, and picks out the output based on the priority of the highest priority active input.
3. What happens if no input is active?
It may produce an undefined or nonsensical output in the absence of input. This is why priority encoders often have an additional output line, typically called “valid” or “V” or something like that, which indicates if any of the inputs are even active. If all the inputs are low, this line will be driven low as well, indicating that the output is not to be used.
4. What is Encoder and Decoder in Digital Electronics?
An encoder in digital electronics is a circuit that takes multiple input lines and turns them into a smaller set of binary outputs. A decoder in digital electronics does the opposite, taking binary input and activating one specific output line based on that input.
5. What is Flip Flop in Digital Electronics?
A flip-flop in digital electronics is a basic memory element that stores one bit of data. It changes its output based on input signals and a clock, making it useful for building memory and sequential circuits.