Introduction To Electronic Gates, Digital Electronics, CSE, GATE Video Lecture - Computer Science Engineering (CSE) | Best Video for Computer Science Engineering (CSE)

now let us talk about devices called as
electric gates so these devices
electronic gates are actually used in
every electronic circuits so the base
you can think of it like this if you
want to build a house you will use
bricks isn't it
similarly if you want to build any
electronic device you are going to use
something called as gates and now these
gates have some properties that they
take some input and then produce some
output and the inputs they take will be
in terms of some signals voltages and
the output they produce will be in terms
of some voltages now you know you know
why we are we have been talking about
something called as boolean variables if
you remember it now I mean till now we
have been doing this right boolean
variables boolean variable which means
the variable is taking only two values
why are we restricting our variables to
be taking only two values is because
these devices can take only two and two
types of voltages high voltage and low
voltage and every input given to this
device can be represented as a variable
which will take some voltage right there
for device devices going to take inputs
and input is having two values and that
input and output even output is also
going to be two values therefore it is
very convenient for us to represent the
variable R using a variable what the
input device is taking and what the
output coming out of the device
right so what do one thing I'll read out
every point about it you please note it
down it is very important because they
might ask it for theory so sometimes
they are even asking it so it is better
that everything every point is that in
your notes so that later when you are
reversing it you will have everything
there that is why I am writing
everything here I'll just read it out
again electronic devices see electronic
gate networks electronic gates generally
receive voltages as input and produce
voltages as output that is simple which
means you give some input and they are
going to give you some output and next
point is the precise voltage of these
the precise values of these voltages are
not significant towards the
determination of the operation of the
gates which means what voltages you are
giving exactly that is independent or
that is irrelevant so sometimes you will
give
voltages sometimes you give five Oltenia
sometimes we give three voltages but ten
five or three is not what we are
wondering worrying about what we really
worry about is what is the range of the
voltage it is which means fizzles the
significance of the point is that
voltages are restricted to the ranges of
values high and low which means we have
some ranges called as high range and low
range if the voltage is anything between
this high range we do not care exactly
what its value is we just say the
voltage is high or we represent it as I
know using some value and if the voltage
falls in the range of low we just say
that the voltage is low we are not
exactly interested in what the voltage
is right and now this next point is two
values the two valued variables may be
used to represent these voltages
therefore any input that you give and
the output that you you everything can
be written as variables so that it will
be easy for us to construct the
expression and then convert the
expression into this electronic gates
next when you if you associate a
constant one with the high voltage and
zero with the low voltage it is called
positive logic system now first first of
all the devices are defined electronic
devices and they are going to take some
voltages so actually the device will be
designed first and which will behave in
some way using the voltages after that
if you have you fear sign see first of
all device is fixed and the voltages are
already defined high low everything I
will take an example later also but for
now understand this now already device
is defined and to which the voltages are
given and the actions of the device is
also defined which means it might take
two high voltages and then approach is a
high voltage or it may take two
low-voltage ascendance which is a lower
till something like this operations
already defined now how do you interpret
those high voltages and low voltages
depends how this gate is going to
actually work I will just take an
example later for now just see this
point if we associate a constant one
with the high voltage and a constant
viewer with the low voltage which means
for the level which we are having high
voltage level if you put a one there and
the low voltage level if you take zero
that is normal it is logical high
voltage is represented with 1 and low
voltage is given a value of zero if that
is the case then it is called positive
logic system the other one is if you
associate the constant one with low
voltage which means for the lower that
we are giving one and for the high
voltage we are giving zero then it is
called negative logic system so
initially if you buy a gate and that
gate is having some voltages and the
actions of the gate is defined in terms
of the voltages high high low like that
and later depending on what is the logic
system you are using the meaning of the
gate will change which means in one
logic system if the gate is and in the
other term system and gate will be or
something like this I will just take an
example and explain you that okay so if
please note on all these points so that
you know it will be easy for you to
understand the theory equations