Encoder and Decoder

What is Decoder? 

• The decoder is a combinational logic circuit used to decode the outputs from inputs. The decoder has 'n' inputs and a maximum of 2ⁿ outputs.

• When the decoder is enabled, outputs will be active based on the combination of inputs.

Types of Decoders

• 2 to 4 decoder
• 3 to 8 decoder
• 4 to 16 decoder

Explanation of  2 to 4 Decoder

This is the circuit design of two to four decoder.

                  

                

Here are 2 input lines and it has 4 outputs.

                  

This is how this decode function works.

Truth Table for decoder

               

 

• The E pin always must be HIGH for the decoder to get output. 
• For A and B if it is '0' and '0' in that case D₀ will get selected '1' and other terminals will stay '0'. 
• For A and B if it is '0' and '1' in that case D₁ will get selected '1' and other terminals will stay '0'. 
• For A and B if it is '1' and '0' in that case D₂ will get selected '1' and other terminals will stay '0'. 
• For A and B if it is '1' and '1' in that case D₃ will get selected '1' and other terminals will stay '0'. 

Logic Circuit Diagram of the Decoder

             

Logic Circuit Simulation of the Decoder

• Here is the video about the simulation process of the decoder .

             

What is Encoder? 

• The encoder is a combinational logic circuit that performs the reverse operation of the Decoder. The encoder has a maximum of 2ⁿ  inputs and 'n' outputs.

• When the encoder is enabled, outputs will be active based on the combination of inputs.

Types of Encoders

• Binary encoder
• 4 to 2 encoder
• Decimal to BCD encoder
• Octal to Binary encoder

Explanation of  4 to 2 Encoder 

This is the circuit design of four to two encoder.

                  

Here are 4 input lines and it has 2 outputs.                 

Truth Table for encoder          

                   

• For the values of A and B to '0' and '0' in the table D₀ should be '1' and other terminals will stay '0'. 
• For the values of A and B to '0' and '1' in the table D₁ should be '1' and other terminals will stay '0'. 
• For the values of A and B to '1' and '0' in the table D₂ should be '1' and other terminals will stay '0'. 
• For the values of A and B to '1' and '1' in the table D₃ should be '1' and other terminals will stay '0'. 

Logic Circuit Diagram of the Encoder

           

             

Logic Circuit Simulation of the Encoder

• Here is the video about the simulation process of the encoder.