This content explains the construction, working principles, and characteristics of depletion-type Insulated Gate Field-Effect Transistors (IGFETs), commonly known as MOSFETs, differentiating between N-channel and P-channel variants.
Mind Map
Klik untuk perbesar
Klik untuk menjelajahi mind map interaktif lengkap
Hey friends, welcome to the YouTube channel ALL ABOUT ELECTRONICS. In the
earlier video of the field effect transistor, we have briefly discussed
about the different types of FET. And in detail we have already discussed
about the JFET. So in this video let us see the second type of FET, which is
known as IGFET and here this IGFET stands for insulated gate field effect
transistor so in this IGFET, the gate terminal is
isolated from the channel using this insulating layer and the MOSFET is the
most common type of IGFET. So here this MOSFET stands for
metal-oxide-semiconductor field-effect transistor and this MOSFET can be
further classified as either depletion type or enhancement type of MOSFET. so in
this video we will learn about the depletion type of MOSFET and first of
all let us see its construction. so if you see this n-channel depletion type of
MOSFET then the channel is made up of n-type material and the substrate is
p-type material. And through the metallic contacts the drain and the source
terminals are connected to this n- channel and similarly the gate terminal
is also connected through this metallic contact. But if you observer here there
is no direct connection between this N channel and this gate terminal. And the
gate terminal is isolated from the channel using this Sio2 layer. So if you
see the structure of this MOSFET then it consists of the metallic contacts for
this drain, gate and the source terminals. then this insulating layer and
the conducting channel which is made up of the semiconductor material. And that
is why this MOSFET is known as the metal-oxide-semiconductor field-effect
transistor. Now due to this insulating layer there will not be any flow of
current through this gate terminal. Or we can say that the input impedance of this
gate terminal is very high and in fact it is even higher than the JFETs. And
that is why these MOSFETs are used in the application where the minimum power
consumption is required. All right, so now let's see the working of this depletion
type of MOSFET. so initially let us assume that the gate and the source
terminals are connected together. And together they are connected to the
ground terminal. That means initially let us assume that this Vgs is equal to zero
volt. And the positive voltage is applied between this drain and the source
terminal. So as soon as we apply the positive voltage then the electrons in
this N channel will get attracted towards this positive terminal. So if you
observe from the source terminal, the electron starts moving towards the drain
terminal. And in this way the current will establish in this N channel. And if
we keep on increasing the voltage between this drain and the source
terminal then the current which is flowing through the channel will
increase. And this process will continue until all the electrons in this channel
will contributes in the flow of current. And then after if we increase this
voltage then the current which is flowing through the channel will become
constant so if you see the direction of the conventional current then it will
flow from the drain terminal towards the source terminal. And for the Vgs is equal
to zero, if you see the output or the drain characteristic then it will look
like this. That means as we keep on increasing the value of voltage VDS then
the drain current ID will increase. And after certain voltage, the drain
current ID will become constant. And the value of the saturation current for vgs
is equal to zero is known as the Idss. Now let's see what happens when the
voltage vgs is negative. So the negative voltage at the gate terminal will push
the electrons towards the substrate and at the same time the holes in this
p-type substrate will also get attracted towards these electrons. So in short, due
to the negative voltage at the gate terminal the electrons in the channel
will get recombined with this holes. And the rate of the recombination will
depend on the applied negative voltage. so as we increase this negative voltage
then the rate of recombination will increase. And that will reduce the number
of free electrons which is available in this n-channel. And effectively it
reduces the flow of current. So as you can see from the graph, as the value of
Vgs will become more and more negative, then the value of drain current will
reduce. And at one voltage this drain current will become zero. so this voltage
Vgs is known as the pinch-off voltage. so if you see the drain or the output
characteristic of the MOSFET then it looks quite similar to the JFET.
But this MOSFET also works for the positive values of Vgs. So now let us
see what happens when we apply the positive voltage. so whenever we apply
the positive voltage at this gate terminal then the electrons which are
minority carriers in this p-type substrate will also get attracted
towards this n-channel. And due to that, the number of free electrons in this N
channel will increase. so effectively we can say that the flow of current in this
n-channel will increase. so for the positive value of voltage vgs the drain
current ID will be even more than this Idss. Now for the JFET
we had already seen the transfer characteristic
and we had seen that this transfer characteristic defines the relationship
between the input and the output quantity. so basically it defines the
relationship between the drain current ID and the voltage vgs for the fixed
value of Vds. so now similarly let us see the transfer characteristic of this
depletion type of MOSFET. so if you see the transfer characteristic then it will
be similar to the JFET. But now you will also get the value of current ID
for the positive values of Vgs. So due to that the curve will get extended towards
the right-hand side. Now as we have seen whenever this vgs is positive then the
number of free electrons in the channel will increase and due to that this
region where the Vgs is positive, is known as the enhancement region and this
region where the vgs is negative is known as depletion region. But still the
relationship between this current ID and the voltage vgs can be expressed by the
same expression which was used for the JFET. That means drain current Id is
equal to Idss times 1 minus Vgs divided by Vp, whole square. So using this
expression we can find the value of drain current ID for the given value of
Vgs. Alright so, so far whatever discussion that we did was only for the
N channel MOSFET. So similarly let us briefly talk about the p-channel type of
MOSFET so in case of a p-channel depletion
type of MOSFET the channel is made up of p-type semiconductor material and the
substrate is n-type. And for the P channel MOSFET, now the polarity of the
applied voltage will also get reversed that means this voltage Vds will be
negative and this voltage Vgs will be positive but first of all let us see how
the current will flow whenever vgs is equal to 0. So when Vgs is equal to 0 and
Vds is applied in this fashion that means when Vds is negative
then the holes in this p-type channel will get attracted towards the negative
terminal and the flow of holes will be established in in this fashion. And in
this case the conventional current will also flow in the same direction. now
whenever we apply the positive value of voltage vgs then the holes will be
pushed towards the n-type substrate and at the same time the electrons in this
n-type substrate will also get attracted towards the p-type channel. And due to
that this holes and the electrons will get recombined and as we keep on
increasing this voltage Vgs then the number of holes in this p-type channel
will reduce and effectively the flow of current in this p-type channel will
reduce. So if you see the drain or the output characteristic of this p-channel
MOSFET then it will look like this. but here this voltage VDS is negative and
the voltage vgs is positive. So as you can see as we keep on increasing this
voltage Vgs then the drain current ID will reduce
and at the pinch off voltage this drain current ID will become zero. and whenever
this vgs is negative then the value of drain current ID will be even higher
than this Idss. And similarly if you see the transfer characteristic then it
will look like this. So now let us see the electronic symbols of this n-channel
and p-channel MOSFETs. So if you see the symbols of this depletion type of MOSFET
then they resembles the actual construction of the MOSFET. so it
consists of a three terminals that is gate, drain and the source terminals. And
further if you observe this symbol there is a space between this gate terminal
and this channel. So this line which connects the drain and the source
terminal represents the channel. And the space between this gate terminal and the
channel represents that the gate terminal is isolated from the
channel. Now in some MOSFETs this substrate pin is also available
externally so in that case the MOSFETs are represented by these symbols. But
whenever it is internally connected to the source terminal then these symbols
are used. Now if you observe the n-channel and the p-channel MOSFETs then the only
difference between the two symbol is the direction of the arrow. so if it is going
inward then it indicates the n-channel MOSFET and if it is going outwards then
it represents the p-channel MOSFET. And basically it indicates the direction of
the flow of current whenever the PN Junction which is formed by the channel
and the substrate is forward biased. So in case of the N channel MOSFET whenever
this PN Junction is forward biased then the current will flow in this direction
and similarly for the P channel MOSFET whenever this PN Junction is forward
bias then current will flow in the outward direction. So basically by the
direction of the arrow we can differentiate these two symbols. So I
hope in this video you understood the construction, working and the different
characteristic of this depletion type of MOSFET. So similarly in the upcoming
video we will learn about the enhancement type of MOSFET. So if you
have any question or suggestion do let me know here in the comment section
below. If you like this video hit the like button and subscribe channel for
more such videos
Klik teks atau cap waktu mana pun untuk melompat ke momen tersebut dalam video
Bagikan:
Sebagian besar transkrip siap dalam waktu kurang dari 5 detik
Salin Satu Klik125+ BahasaCari KontenLoncat ke Cap Waktu
Tempel URL YouTube
Masukkan link video YouTube apa saja untuk mendapatkan transkrip lengkap
Formulir Ekstraksi Transkrip
Sebagian besar transkrip siap dalam waktu kurang dari 5 detik
Pasang Ekstensi Chrome Kami
Dapatkan transkrip seketika tanpa meninggalkan YouTube. Pasang ekstensi Chrome kami untuk akses satu klik ke transkrip video apa pun langsung di halaman tontonan.
