1. Introduction
  2. Block diagram
    1. Examples of decoders ::
  3. 2-to-4 line decoder
  4. Block diagram
  5. Truth table
  6. Logic circuit


A decoder is a combinational circuit. It has n input and to a maximum m = 2n outputs. Decoder is identical to a demultiplexer without any data input. It performs operations which are exactly opposite to those of an encoder.

Block diagram

Examples of decoders ::

  • Code converters
  • BCD to seven segment decoders
  • Nixie tube decoders
  • Relay actuator

2-to-4 line decoder

The block diagram of 2 to 4 line decoder is shown in the fig. A and B are the two inputs where D through D are the four outputs. Truth table explains the operations of a decoder. It shows that each output is 1 for only a specific combination of inputs.

Block diagram

Truth table

Logic circuit