1:4 Demultiplexer Video Lecture | Analog and Digital Electronics - Electrical Engineering (EE)

in the previous video we had seen what
is the demultiplexer and the general
form of a demultiplexer in this video
let us look at block diagram truth table
and logic diagram of a 1 to 4 d
multiplexers
similar to a multiplexer in order to
arrive at the block diagram of a
demultiplexer we need to compare the
given D multiplexer with it general form
by comparing it with the general path we
will get the number of inputs outputs
and select Li
the general form of a demultiplexer is
you
input is to output and
inputs is one number of outputs is to
power n where n is the number of select
lines so we are given 1 is to 4 so this
can be written as 1 is to 2 power 2
which will give us n is equal to 2 so
the number of input will be 1 number of
output will be 4 and number of select
lines will be 2 so by using this
information we can draw the block
diagram of demultiplexer so this is the
block diagram of a 1 2 4 d multiplexer
you
so you can see that you have one input
data line D in to select line s1 s0 and
four output line y0 y1 y2 y3 and one
active high enable input so this enable
input determines if the d-max is enabled
or disabled so if the enabled input is 1
the demas is enabled and when the enable
input is 0 the d-max will be disabled
now look at the truth table of 1/2 for
demultiplexers the truth table and the
working of a 1 to 4 demultiplexer can be
understood by looking at the block
diagram of 1 to 4 demultiplexers so this
is what the block diagram of 1 to 4 be
multiplexers
from the definition of demultiplexers we
know that the input data line is
connected to a particular output data
line depending on the combination of
select lines here you have to select
line so you will be having four
combinations that is 0 0 0 1 1 0 and 1 1
so when the input combination s 1 s 0 is
0 0 then the D in line gets connected to
y 0 similarly when s 1 s 0 is 0 1 the in
line gets connected to y 1 when s 1 s 0
is 1 0 D in line gets connected to y2
and when s 1 s 0 is 1 1 D in line gets
connected to Y C all this would be true
only if the enable signal is 1 if it is
0
then irrespective of the combination of
s1 s0 all the four outputs will be 0
because the demultiplexer will be
disabled so this is represented in the
form of a truth table
the inputs to the demultiplexer will be
enable and s1 s0 whereas there will be
four output y0 y1 y2 y3 if the animal is
0 the demultiplexer is disabled so
irrespective of the combination of the
select lines the output would be 0 these
4 cases indicate when the demultiplexer
is enabled since it is an active high
enable input
II must be 1
and when the combination of select line
s1 s0 is 0 0 then the teen data line
gets connected to y 0 and y 0 becomes t
in and the other 3 will be 0 similarly
when it is 0 1 beam gets connected to y
1 so Y 1 will get in
and the others will be 0 for 1 0 Dean
gets connected to Y 2 so y 2 will be
Dean and others will be 0
and the Select line is one one
Dean gets connected to y3 so y3 is d and
others will be zero so this is the truth
table of one to four demultiplexers to
draw the logic diagram of one 240
multiplexer we have to derive the output
expression for y 0 y 1 y 2 and y 6 we
can do that from the truth table
so why is zero will be d in depending on
the input combinations of e s1 and s0
for y 0 to be teen es 1 s 0 must be 1 0
0 which means e s 1 bar is 0 bar
so this is similar to what we had done
in multiplexer that is if you have one
then you write the variable and if you
have zero you write the complement of
that variable so similarly for y one it
will be d in e s 1 bar s 0
for why do it will be
d in e
one
zero-bar + 4 y 3 TB d in e s1 s0
so you have
for output expressions so if you draw
the logic diagram using basic gates it
will give you the logic diagram of one
to four T multiplexers
we have already done the logic diagram
of one circle demultiplexer here you can
see that you have to select line s1 is 0
for output y0 y1 y2 y3 1 enable input
and 1 data input line D so this D in is
connected to all the four and gate and
also the enable is connected to all the
four angles
the output of this not gate will be s 1
bar and output of this not gate will be
is 0 bus
so the output of first and gate will be
d in a 0 bar s 1 bar and E so this can
be written as d in e s 1 bar s 0 bar
similarly the output of second and gate
will be beam
s 0 s 1 bar and E so this will be D in e
s 1 bar s 0 the output of third and gate
will be Dean is 0 bar s 1 e which can be
written as d in e s 1 s 0 bar
similarly the output of force and gate
will be D in s0 s1 and E so which can be
written as D in es1 SC so this is the
same as what we got from the truth table
we look at 1 to 8 d multiplexer in the
next video thank you