Digital Design Session 14

Digital Design – © 2020 Mouli Sankaran Email: mouli.sankaran@yahoo.com 2
Session 14: Focus
 Multiplexers (MUX)
◦ Usage in Real-life Applications
 Demultiplexer (DEMUX)
◦ 1-to-4-line Demultiplexer
◦ Symbols or Representation
 Solving problems
◦ With Basic Gates
 Solving Logical problems
 Home work problems
◦ Logic Gates
◦ K-maps

Multiplexer (MUX)

Multiplexer: Real-life Applications - 1
 Time Division Multiplexer (TDM) is one of the types of
multiplexers which join data streams by allotting every
stream a different time slot, in a sequence.

Multiplexer: Real-life Applications - 2
 Choosing one input from multiple input lines, to be
given to Arithmetic Logic Unit (ALU)
Selector
Inputs Output Lines
Bringing out
One of the
Input values

Demultiplexer (DEMUX)

Demultiplexer (DEMUX)
 A demultiplexer
(DEMUX) basically
reverses the multiplexing
function
 It takes digital
information from one
line and distributes it to
one of the output lines
 Based on the data-select
inputs
 For this reason, it is also
known as data
distributor
3 Select Lines
8 Output
Lines

1-to-4 line Demultiplexer
 For example, if the data select lines are (S1S0 - 10b) then data
input will be sent out through D2 output line

Quiz 1: Draw the Output Waveforms
 Given data-input and data-select waveforms, draw the output
waveforms on D0 to D3

DEMUX: Symbol or Representations

Demux : Application
One of the Paths (A/B/C/D) is chosen,
to get different amplification of input signal
A: OpAmp:
Operational Amplifier

Solving Problems with Basic Gates

Problem 1: Draw the output waveform

This is a 4-input NAND Gate, operating as negative OR. Use DeMorgon’s Theorem
 What is the equivalent logic gate? 4-input NAND

This is a 4-input NOR Gate, operating as negative AND. Use DeMorgon’s Theorem.
 What is the equivalent logic gate? 4-input NOR

Problem 6: Draw the output waveforms
XNOR Gate
XOR Gate

Solving Some Logical Problems

Problem 7: When does the alarm sound?
 The alarm sounds when any one of the three doors are opened.

Problem 8: When does the alarm sound?
 Below is the circuit of car seat belt alarm system.
 When will the alarm sound?
 The alarm will sound if the seat belt is not buckled within 30 seconds of
switching ON the ignition !!!
Delay
Initially LOW. when Ignition is
ON, it becomes HIGH After 30
seconds of delay

Problem 9: Staircase Two-way Switch
How does it work?

Home Work Problems

HW 1: Draw the output waveform

Solving Problems
with
K-maps

HW 5: Group 1s in each of the K-maps

HW 6: Group the 1s the K-map

HW 7: Find the SOP terms

HW 8: Find the SOP terms

HW 9: Map to K-map from Truth table
What is the simplified expression in sum-of-products form? AB

HW 10: Find the POS terms

HW 11: Find the SOP & POS terms
A
AC
SOP:
POS:

HW 12: Group the 1s in the K-map

HW 13: Find the product terms

HW 14: Simplify using 5-variable K-map

Session 14: Summary
 Multiplexers (MUX)
 Demultiplexer (DEMUX)
◦ 1-to-4-line Demultiplexer
◦ Symbols or Representation
 Solving problems
◦ With Basic Gates
 Solving Logical problems
 Home work problems
◦ Logic Gates
◦ K-maps

References
Ref 1 Ref 2

Digital Design Session 14

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Digital Design Session 14