design decoder?

Question

What is mean by decoder? how to design a decoder?(digital logic)

Answer 1

A decoder is a set of combinational logic (logic gates only, with no flip-flops) that takes an encoded input, such as a 3-bit binary number, and decodes the binary number into 1-of-8 separate outputs.

For example, when the input is binary 010, the only output that will be active is the '2' output.

Other examples are: 2-bit binary to 4 output decoder, 4-bit binary to 16 output decoder, BCD to 10 output decoder, 4-bit gray code to 16 output decoder.

You design one by creating a truth table of the inputs versus the outputs and use a sum-of-products (OR gates, AND gates) to implement the table. Karnaugh maps and other techniques should be used to minimize the number of logic gates.

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Answer 2

Here are some fine examples of logic decoders:

General decoder info
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http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld024.htm

http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld025.htm

2 to 4 decoder
------------------------
Truth table & device

http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld026.htm

Logic diagram

http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld027.htm

3 to 8 decoder
----------------------

http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld033.htm

Logic diagram

http://www.cs.ualberta.ca/~amaral/courses/329/webslides/Topic8-DocTimeDiagrams/sld032.htm

I hope this helps ...

Get a hold of the "classic" 2nd edition Logic Data Handbook on TTL from Texas Instruments. In it you'll find all the decoders, truth tables, schematics & descriptions.