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E-Mosfet as an Amplifier

In the last post, we studied the hybrid-pi model of E-MOSFET, in this post we are going to see Ac-Analysis of MOSFET or in short designing an amplifier with E-MOSFET. We know that with the help of Dc-Analysis we find certain parameters which are very important while designing any amplifier and those parameters are transconductance(gm), output current(Id), and Vth. So now we will focus on the ac-analysis of MOSFET to find certain ac parameters which are required to design any amplifier. @ AC-ANALY SIS OF E-MOSFET :- As you can see in the above diagram all the capacitors shown in the circuit will be shorted because capacitors act as a short circuit for the ac-signal. So the ac model of the E-MOSFET would look as shown below. As we had studied the ac-analysis of the BJT, there we had seen 4 important parameters and they were  1) Current Gain (Ai) 2) Input Resistance (Rin) 3) Output Resistance (Rout) 4) Output Voltage (Vout) 1) Current Gain:- As we all know the MOSFET is a voltage-controll

Hybrid-pi Model of MOSFET

In the previous post, we studied the key differences between D-MOSFET and E-MOSFET. In this post, we will only analyze the Ac model (small-signal analysis) of E-MOSFET as the working of D-MOSFET is similar to that of JFET so there isn't any significance in studying D-MOSFET. I hope that now you all guys are very much familiar with BJT and its model. We will compare the r π(r-pi) model of BJT to study the ac analysis of MOSFET. # R-pi Model of BJT :- So now as you can see that in BJT all the regions i.e. base, emitter, and collector region are connected to each other and a small current Ib which is in a few micro-amps flows through the base terminal but in the case of E-MOSFET, there is an oxide layer which is present in between the Gate and Substrate which acts as an insulator, therefore, the current Ig flowing through the gate terminal is zero i.e. (Ig = 0mA).  Now we know that V = I * R, if Ig = 0mA  Therefore, R = infinite ( ∞ ) Thus for MOSFET the value of  r π =   ∞ so in Ac a

Difference Between E-MOSFET & D-MOSFET

In the last post, we saw MOSFET biasing and some equations. I hope now you are very much comfortable in MOSFET. In this post, we will understand the key differences between D-MOSFET and E-MOSFET. Although we had covered almost all of the key differences in the previous posts here we will revise a few points and at the end, we will conclude that which MOSFET is better. Remember I'm considering N-type MOSFET as it is much more efficient than P-type MOSFET. 1) On basis of Symbol :- In the case of N-type MOSFET remember that the arrow will always point towards the gate terminal (<---) or to the oxide layer and for P-type MOSFETs, the arrow will point in opposite direction to the oxide layer (--->) or you can say that it is pointing away from the oxide layer. Since there is an oxide layer present below the gate terminal which acts as an insulator therefore the small gap which is shown in the symbol represents that oxide layer. In D-MOSFET, the two regions that are drain and sou

Biasing of MOSFET

We had studied biasing of BJTs and JFET. In the post of BJT biasing we had seen that there were four biasing techniques of BJT and JFET. So the same four biasing techniques are present for MOSFET.  But as we had seen in the post on BJT biasing Voltage divider bias gives more stability than Modified fixed bias and I hope now you are very much familiar with the concept of biasing.  So in this post, we will only analyze the Voltage divider biasing technique of MOSFET but before that, we need to understand the drain-source characteristics of MOSFET in little depth. In the last post, we saw that MOSFET can be operated in 3 different regions. Now we will see how we can control it so that it can work in the desired region. So for that, we need to recall the graph which we studied in the last post. In the above figure as you can see very clearly that when your input voltage(Vin = Vgs) is less than the threshold voltage(Vth) i.e. (Vgs<Vth) so in that case, your MOSFET is operating in the Cu

Characteristics Of MOSFET

 In the last post, we studied some basic concepts of MOSFET like different types of MOSFET, its construction, and its working. I hope you understood each and everything in that post. Now, in this post, we will study the characteristics of both types.  1) Characteristics of N-type Depletion MOSFET :- In the last post, we concluded that, although the internal structure of JFET and MOSFET are not similar, N-type Depletion MOSFET is almost similar to the N-type JFET. Now, since their working is similar therefore we can say that their characteristics should also be similar. Therefore we proved that characteristic of N-type JFET is the same as N-type Depletion MOSFET. That means the equation for output current(Id) would also remain the same. Id = Idss*(1 - Vgs/Vp)^2 So in this post, we will fully focus on the characteristic of n-channel enhancement type MOSFET. 2)  Characteristics   of   N-channel Enhancement   MOSFET :- Before studying characteristics of Enhancement type MOSFET let


In the last post, we had seen Ac analysis of JFET and there we had completed the whole JFET. Until now we had studied all the concepts of BJT and JFET in great depth. Now from this post, we will be starting with MOSFET. The full form of MOSFET is M etal O xide S emiconductor F ield E ffect T ransistors. In the end, it will be very much clear to you, why it is called metal-oxide field-effect transistors. 1) Types of MOSFET :- There is a total of 2 types of MOSFET i.e. Depletion-MOSFET (D-MOSFET) and Enhancement-MOSFET (E-MOSFET). Further, both are divided into 2 i.e. N-type and P-type. While explaining the construction part of MOSFET you will understand these 2 types of MOSFET in great depth but for now, just remember the symbol of both the MOSFET. Symbol :- NOTE :- MOSFET can be a 3 terminal device or 4 terminal device. Sometimes substrate is shorted with the source internally at that time we can say that it is a 3 terminal device if the substrate is not connected with the source inter

Ac Analysis of JFET

Until now we had covered almost all of the topics of dc analysis of JFET . If you want to start with Dc analysis of JFET, I recommend you start with this post on JFET:- Junction Field Effect Transistor .  So in this post, we are going to study ac analysis of JFET. Before starting with the post I want to give you a brief idea that what concepts we are going to learn by the end of this post.  1) Ac Analysis of CS-amplifier 2) Ac Analysis of CG-amplifier 3) Different parameters and it's importance while designing an amplifier.  We will try to understand it's working by using bypass and unbypassed capacitors. 1) Ac Analysis of CS Amplifier:- Here I'm considering a self-bias circuit you can also consider voltage divider bias and according to the superposition theorem during ac analysis, all the dc sources are grounded. (Remember that during Ac-analysis capacitors are replaced by short-circuit and during Dc-analysis capacitors are replaced by open-circuit.) a) Calculation of   I

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