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Encoder (digital)

Digital electronic circuit

Wikipedia contributorsAdapted for Fathomly · View authors
1 min read
Source updated May 1, 2025
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An encoder (or "simple encoder") in digital electronics is a one-hot to binary converter. That is, if there are 2n input lines, and at most only one of them will ever be high, the binary code of this 'hot' line is produced on the n-bit output lines. A binary encoder is the dual of a binary decoder.

If the input circuit can guarantee at most a single-active input, a simple encoder is a better choice than a priority encoder, since it requires less logic to implement. However, a simple encoder can generate an incorrect output when more than a single input is active, so a priority encoder is required in such cases.

01Types of encoder

2n-to-n encoders

A 2^{n}-to-n encoder has n number of outputs in correspondence to the 2^{n} number of inputs. It thus reduces the number of transmission lines and can be compared to a multiplexer. Only one of the inputs become "high" (logic state "1") at a time.

For example, a 4-to-2 simple encoder takes 4 input bits and produces 2 output bits. The illustrated gate level example implements the simple encoder defined by the truth table, but it must be understood that for all the non-explicitly defined input combinations (i.e., inputs containing 0, 2, 3, or 4 high bits) the outputs are treated as don't cares.

4-to-2 encoder

Truth Table
InputOutput
I3I2I1I0 O1O0
0000 x
0001 00
0010 01
0100 10
1000 11

https://en.m.wikipedia.org/wiki/Encoder_(digital)#/editor/4 https://en.m.wikipedia.org/wiki/Encoder_(digital)#/editor/4

Gate level schematic of a simple 4:2 line encoder
Gate level schematic of a simple 4:2 line encoder
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This article is adapted from the Wikipedia article “Encoder (digital)”, written by its contributors and licensed under CC BY-SA 4.0. Fathomly has changed the layout, removed citation markers, navigation and maintenance notices, and adjusted punctuation. This adapted version is shared under the same license. For references, see the original article.

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Related topics

Binary decoder

In digital electronics, a binary decoder is a combinational logic circuit that converts binary information from the n coded inputs to a maximum of 2n unique outputs. They are used in a wide variety of applications, including instruction decoding, data multiplexing and data demultiplexing, seven segment displays, and as address decoders for memory and port-mapped I/O. There are several types of binary decoders, but in all cases a decoder is an electronic circuit with multiple input and multiple output signals, which converts every unique combination of input states to a specific combination of output states.

Multiplexer

In electronics, a multiplexer, also known as a data selector, is a device that selects between several analog or digital input signals and forwards the selected input to a single output line. The selection is directed by a separate set of digital inputs known as select lines.

Priority encoder

A priority encoder is a circuit or algorithm that compresses multiple binary inputs into a smaller number of outputs, similar to a simple encoder. The output of a priority encoder is the binary representation of the index of the most significant activated line.