Binary Encoder – Construction, Types & Applications

Digital Binary Encoder – Types & Construction

What is Binary Encoder?

A combinational circuit capable of converting “2ⁿ” input signals into “n” signals (such as BCD (Binary Coded Decimal) Binary etc) is called binary encoder also known as digital encoder.. Its operation is exactly opposite of Binary Decoder. In simple words, Binary Encoder used to encode a Binary Codes.

It has 2ⁿ input lines and “n” output lines. When we want to process data received from many data lines and we have few available input ports or we want to conserve the input ports of a system then we apply an encoder to reduce the number input data lines. Block diagram of binary encoder is given below.

Line encoders are an example of Encoder in which multi-input lines are converted into a few binary outputs.

In line-encoders, one input at a time has a HIGH value otherwise the output will be invalid. Each data input line is treated as a single digit, for each line a specific binary output is generated in line encoders.

To clarify the problem of having more than one input line “HIGH”, priority encoders are used. Priority Encoders prioritize the input based on the design like in Line encoders, Most significant value out of the two inputs will decide the output. There is also an input condition check “V” which is low when there is no high input. And it is high when there is at least one high input.

• Also read: DEMUX – Demultiplexer | Types, Construction & Applications

Types of Binary Encoder

Some of the Line encoders are given below with details.

• 2-to-1 Line Binary Encoder
• 4-to-2 Line Encoder
• 4 to 2 Priority Encoder
• 8-to-3 Line Encoder
• 8 to 3 Priority Encoder

Also read: Counter and Types of Electronic Counters

Some of the line encoders are given below:

2 to 1 Line Encoder

Schematic & Truth Table

Simplest line encoder is 2 to 1 line encoder in which there are 2 input lines and 1 output line. 2 to 1 line Encoder schematic and truth table are given below.

When D₀ is high, the output is 0 and when D₁ high output is 1 considering the other input is 0.

4 to 2 Line Encoder

This encoder has 4 input lines and 2 output lines. A single input line can be high at a time otherwise the output will be ambiguous. Block diagram of 4 to 2 line binary encoder is given below.

The output is in binary format. Each input line gives a combination of binary output.

Consider D₀-D₃ as 4 inputs and X, Y as output bits.

Truth Table

The truth table of 4-2 Encoder is given below:

According to the truth table of 4 to 2 encoder:

X               =            D₂ + D₃

Y              =            D₁ + D₃

As from the above expressions, we deduce that binary encoder only needs OR gates. This encoder can be implemented with 2 OR gates as shown in the figure below. Schematic diagram of 4 to 2 line encoder using or gates it given below.

However, there is a limitation, when D₁ and D_{2 ­}are high at the same time then the output will be 1 1, which neither represent D_{1 ­}nor D₂ output. To remove this ambiguity, Priority encoders are designed.

• Also read: MUX – Digital Multiplexer | Types, Construction & Applications

4 to 2 Priority Encoder

This encoder prioritizes the highest input and produces output for that highest priority input regardless of the value of the other inputs. This encoder will prioritize D₃ over D₂,D_1, and D_0. D₀ being the lowest priority input.

If D₂ input is high then the output will be 10 whether the D₁ input is low or high.  There is input condition check “V” to make sure there is any input. “V” is high when there is any input.

Input and output variable are “D₀-D₃” and “X, Y, V” respectively.

Truth Table and K-Map

The truth table and K-Map for 4 to 2 priority encoder is:

Using K-map solution:

X             =             D₂ + D₃

Y             =             D₁D̅₂ + D₃

V             =             D₀ + D₁ + D₂ + D₃

These expressions are same as the normal encoder but there is a condition that Y = 1 for D₁ only when D₂ (higher priority than D₁) is low because for D₂ =1, “Y” should be “0” according to the truth table.

• Also read: Ring Counter &  Johnson Counter – Construction & Operation

Schematic of 4 to 2 Priority Encoder

Schematic of priority encoder using NOT, AND and OR gate is given below.

8 to 3 Line Encoder

This encoder has 8 input lines and 3 output lines. It converts the octal into a binary system that is why it is known as octal to binary converter.

Consider D₀-D₇ as input and X,Y, Z as output.

Truth Table

The truth table for 8 to 3 line encoder is given below:

According to the truth table :

X             =             D₄ + D₅ +D₆ + D₇

Y             =             D₂ + D₃ +D₆ + D₇

Z             =             D₁ + D₃ +D₅ + D₇

• Also read: Ripple Carry And Carry Look Ahead Adder

8 to 3 Line Encoder Schematic Using OR gate

Schematic of 8 to 3 line encoder using OR gate is given below.

8 to 3 Priority Encoder

Consider  D₀-D₇ as input and X,Y, Z as output and V as input condition check.

Truth Table

The truth table for 8-3 priority encoder is given below.

According to the truth table :

X             =             D₄ + D₅ + D₆ + D₇

Y             =             D₂ D̅₄ D̅₅ + D₃ D̅₄ D̅₅ + D₆ + D₇

Z             =             D₁ D̅₂ D̅₄ D̅₆ + D₃ D̅₄ D̅₆ + D₅ D̅₆ + D₇

V             =             D₀ + D₁ + D₂ + D₃ + D₄ + D₅ + D₆ + D₇

“X” being the MSB of binary output is high when any of D_4,D₅,D₆ and D₇ is high.

“Y” is high when D₇ or D₆ is high. It is also high when D₃ or D₂ is high considering D₄ and D₅ are low because if they are high then the output Y=0.

“Z” is high whenever D₇ is high, it is also high when D₁,D₃,D₅ are high but with these inputs other high priority input should be checked for which output “Z” goes low such as;

For D₁; D₂,D_4,and D₆ has to be low,

For D3; D₄ and D₆ has to be low,

For D₅; D₆ has to be low.

If any of them are high the output “Z=0″

• Also read: Digital Flip-Flops – SR, D, JK and T Flip Flops

8 to 3 Priority Encoder Schematic

Schematic of 8 to 3 priority encoder is given below.

Cascading 4 to 2 Priority Encoders

8 to 3 priority encoder can be made by cascading 4 to 2 priority encoder with enable inputs.

When enable input is high the encoder is enabled

Inputs to the encoders are D₀-D₃ for first encoder and D₄-D₇ for the second encoder. The output of the first encoder is Y₀, Z₀ and second encoder output is Y₁, Z1. Input condition check for the first decoder is V₀ and second is V_1.

Truth Table

The output of the whole 8 to 3 priority encoder is X, Y, Z. so the truth table would be:

According to the truth table:

X               =             V₁

Y               =             Y₀ + Y₁

Z               =             Z₀ + Z₁

V              =             V₀ + V₁

En₀             =             V̅₁                      

when there is no input to the higher priority Encoder the lower Priority encoder will turn on.

• Also read: Comparator and Digital Magnitude Comparator

Schematic Diagram & Operation

Cascading 4 to 2 Priority Encoders implementation diagram is given below.

Binary Decoder IC Pinout

CMOS IC 4532 Priority Encoder

A CMOS IC 4532 Priority encoder’s pin configuration and details are given below.

Applications of Binary Encoders

Encoders are widely used in digital electronic systems. Some of common application and uses of encoders are as follow:

• In calculators, Encoders are used to encode the decimal values in binary to perform specific binary functions like addition, subtraction, multiplication and division etc.
• Encoders also used to generate digital signal (shaft encoders and linear encoders).
• Priority encoders are used to reduced the number of connection and wires in specific electronic circuit or applications with multiple inputs such as Keyboard (104 keys (as input) of a standard QWERTY keyboard) and Keypads as well as they are used to detect interrupts in microprocessor applications.
• The diode matrix encoders are used in printed circuit boards (PCB) on many electronic devices having keyboards as user data interface.
• Positional Encoders are used in magnetic positional control for positioning in robotic arms and ship navigation.

You may also read:

• Digital Logic NOR Gate
• Exclusive-NOR (XNOR) Digital Logic Gate
• Digital Logic NAND Gate – Universal Gate