Early Effect or Base width modulation - Electrical Engineering (EE) Video Lecture

we are discussing about a 2006 ec paper
and this question is related to
electronics
the phenomena known as early effect in a
BJT refers to a reduction of effective
base width caused by a electron hole
recombination at the base be reverse
biasing of base collector Junction see
forward biasing of emitter base Junction
the early removal of third base charge
during saturation do cut-off switching
the right answer for this question is P
reduction of effective base width is
caused by reverse biasing the base
collector Junction
early affect the other name for this one
is nothing but pace width modulation
the other name for the early effect is
base width modulation as the name
implies the base width of a BJT
is going to be getting modulated that is
nothing but changed so there is
effectively the base width ops base
width of ability will gets changed that
is going to be taking place only in
active region
in active region this phenomena will
take place base width modulation or
early effect the meaning of active
region is nothing but emitter base
Junction je forward bias
collector--base junction JC reverse bias
okay and if you observe let us assume we
are going in this way
this is a BJT which consisting of P and
P transistor let us assume
and we are interested in base width so
that I am trying base as wider but
actually base width is very very small
but here our interest is in the base
width so that we are going with emitter
it is based this is collector this will
be treated as je emitter base Junction
and it is called as JC
if no voltages are going to be applied
by the time these two junctions emitter
base Junction and collector base
Junction are under open circuit under
open circuit there is a depletion region
formed between emitter and base as well
as collector and base and under the open
circuit the depletion region form can be
neglected because it is very very small
under open circuit so that we don't show
the depletion region over here
we are drawing with vertical lines only
we are neglecting the depletion region
formed under open circuit
now you have to make emitter base
Junction forward biased and collector
base Junction reverse bias
to make the transistor to work as either
amplifier or oscillator because it must
be in active region for that purpose
so emitter base Junction forward bias is
nothing but if it is let us assume PNP
transistor that is PNP means emitter and
collector is of p-type bases of n-type
for P side you are applying positive
voltage okay
so that this is what VEB we are going
with less -
whenever you are making forward bass of
emitter-base junction at that time
potential barrier in forward by us
in forward bias potential barrier
reduces
potential barrier reduces meaning is
nothing but height of potential barrier
as well as width of potential barrier
will be reduces okay so width already
will neglect it under open circuit now
it will be reduced so no need to draw
the with geta emitter base Junction so
that we are simply trying the same
vertical line
now when you are going to be making
collector base Junction reverse pass
collector base Junction reverse pass is
nothing but four pieces you must apply
negative voltage so that we can ensure
that when this collector base Junction
is going to be under reverse bias the
voltage what you are applying is nothing
but we see B
so whenever you are applying VCB as a
voltage which makes collected by jings
in the worse pass
we know that one under reverse bias in
reverse bias potential barrier
okay increases potential barrier
increases is nothing but width as well
as height are going to be increases
here we are interested only in the width
according to this question so width of
potential barrier that is nothing but
width of depletion region increases
with tufts depletion region is going to
be increases
and whenever we are going for this
depletion region which generally
increases in lightly doped side so the
width of depletion region more
penetrates into lightly doped side so
now check whether it is going to be base
is lightly doped or collector is lightly
doped so generally emitter is heavily
doped okay emitter is heavily doped
campaign to collector and collector is
heavily doped compared to base base is
very much like lead opal so with tuff
potential barrier at the collector base
Junction increases and the increase is
going to be more into base region than
the collector side so collector side is
going to be very very small
whereas beside the width of depletion
region is going to be increases because
base is lightly doped
if you observe under open circuit the
base is going to be from this point to
this end
that is under open circuit the
metallurgical base width is nothing but
the blue B WB is nothing but the width
from the emitter to collector end where
the majority charge carriers of base are
present
and under reverse mass of
collectivization the majority carriers
are effectively present only during this
portion look at this one because
depletion region doesn't contain mobile
charge carriers okay
depletion region always consisting of
ions
since it is n-type base it will be
consisting of positive ions and P side
it will be consisting of negative ions
so I answer immobile and no mobile
charge will be present in the depletion
region
so effectively mobile charge carriers
that is nothing but majority charge
carriers off base will be present only
in the during this portion so during
this portion if you observe this is WB
dash and the width of depletion region
is nothing but this is W
okay so as VCB is going to be increases
that is collector base voltage increases
at the time reverse bias at JC increases
collector base Junction gets more
reverse bias as collector base Junction
gets more reverse bias width of
depletion region increases and it will
be penetrated into more into base side
so that effective base width may the
mobile charge carriers are going to be
present will be gets reduces that is WB
Dash is getting reduced even though the
WB is same WB's metallurgical base width
whereas WB Dash is effective base width
where the majority charge carriers are
available which can contribute further
transistor operation
so this phenomena is first observed by
the scientist named as early that's why
it has named as early effect so as
reverse bias voltage across
collectivization is going to be
increases effective base width gets
reduces this phenomena is called as base
width modulation so the answer for this
question is a reduction of effective
base width is caused by reverse biasing
the base collector Junction there is
nothing but JC so the right option for
this is B
thank you