Encoder

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An encoder is a device used to change a signal (such as a bitstream) or data into a code. The code may serve any of a number of purposes such as compressing information for transmission or storage, encrypting or adding redundancies to the input code, or translating from one code to another. This is usually done by means of a programmed algorithm, especially if any part is digital, while most analog encoding is done with analog circuitry.

1 Single bit 4 to 2 Encoder
2 Priority encoder
3 Connecting Priority Encoders
4 Examples
5 See also
6 External links

Single bit 4 to 2 Encoder

An encoder has 2ⁿ input lines and n output lines.The output lines genrate a binary code corresponding to the input value. For example a single bit 4 to 2 encoder takes in 4 bits and outputs 2 bits. It is assumed that there are only 4 types of input signals these are : 0001, 0010, 0100, 1000.

Gate level circuit diagram of a single bit 4-to-2 line encoder

I₃	I₂	I₁	I₀	O₁	O₀
0	0	0	1	0	0
0	0	1	0	0	1
0	1	0	0	1	0
1	0	0	0	1	1

4 to 2 encoder

The encoder has the limitation that only one input can be active at any given time. If two inputs are simultaneously active, the output produces and undefined combination. To prevent this we make use of the priority encoder.

Priority encoder

A priority encoder is such that if two or more inputs is given at the same time, the the input having the highest priority will take precedence. An example of a single bit 4 to 2 encoder is shown.

I₃	I₂	I₁	I₀	O₁	O₀
0	0	0	d	0	0
0	0	1	d	0	1
0	1	d	d	1	0
1	d	d	d	1	1

4 to 2 priority encoder

Connecting Priority Encoders

Priority encoders can be easily connected in arrays to make larger encoders, such as a 16 to 4 encoder made from six 4 to 2 priority encoders (four encoders having the signal source connected to their inputs, and two encoders that take the output of the first four as input).

Examples

A compressor encodes data (e.g., audio/video/images) into a smaller form.
A multiplexer combines multiple inputs into one output.
A rotary encoder converts rotary position to an analog (e.g., analog quadrature) or digital (e.g., digital quadrature, 32-bit parallel, or USB) electronic signal.
A linear encoder similarly converts linear position to an electronic signal.