logic decoders

1. DECODER AND
MULTIPLEXER

2. CONTENT THAT BE COVERED:
• Decoder
• Example of binary decoder.
• Decoders: implementing function.
• Decoder with enable.
• Multiplexers
• Block diagram of multiplexer.
• Majority function using a Multiplexer.
• Types of lines in multiplexer.
• Three-state gates.
• Graphic symbol for a three-state Buffer.

3. WHAT IS DECODER?

4. DECODER
• A decoder is a combination logic circuit which has many input and
output lines.
• Therefore a decoder has “n” input lines and maximum “m” output
lines, where
• m=2n. When the decoder circuits is enable l, based on the
combination of
• input present, one of the 2n output lines will be active high.
• The decoder is also known as min-term generator or max-term
generator

5. EXAMPLE OF BINARY DECODER

7. DECODER : IMPLEMENTING
FUNCTION.
•Boolean function, in sum of min-terms form decoder
to generate the min-terms, and an OR gate to form
the sum.
•Any combinational circuit with n inputs and m outputs
can be implemented with an n:2n decoder with m OR
gates.

10. Decoders with Enable
A standard decoder typically has
an additional input called Enable.
Output is only generated when
the Enable input has value 1;
otherwise, all outputs are 0. Only
a small change in the
implementation is required: the
Enable input is fed into the AND
gates which produce the outputs.

11. WHAT IS MULTIPLEXER?

12. MULTIPLEXERS
•Combinational circuit that select binary
information from one of many input lines and
directs it to output line.
•That also simplify Data Selector.
• Multiplexers has:
• N data inputs (Multiple)
• 1 Output (Single)
• M select inputs, with 2M = N

13. BLOCK DIAGRAM OF MULTIPLEXER.

14. Implementing
Multiplexers
The implementation of a
multiplexer is straightforward,
and uses a decoder. Here is a 4-
1 multiplexer.

15. TYPES OF LINES IN MULTIPLEXER.
•2-to-1 (1 select lines)
•4-to-1 (2 select lines)

16. 2-TO-1 (SELECT LINES) MULTIPLEXER
•Here 2:1 means 2 inputs and 1 output

17. 4-TO-1 (2 SELECT LINES) MULTIPLEXER
• 4:1 MUX has 4 inputs (DO, D1, D2, D3) & 2 select
lines (S0, S1)

18. THREE-STATE GATES
• Multiplexer can be constructed with three-state gates. A three state
gates is a digital circuit that exhibits three state. Two of the states
are signal equivalent to logic 1&0 as a conventional gate. The third
state gates is a the high-impedance state that behaves like An open
circuit that means Output appears To disconnect and the circuit has
no logic significant.
• The most commonly used is the buffer gate.

20. REFERENCES
• slideserve.com
• slideshare.net
• https://m.youtube.com/watch?v=FKvnmxte98A

21. THE END