MOSFET Common Source Amplifier - Small Signal Analysis ( Voltage Divider Bias )

In this video, the small-signal analysis of Common Source Amplifier (Voltage Divider Bias) is explained with a solved example.
Timestamps for the different topics covered in the video:
0:00 Introduction
1:56 Small Signal Analysis of CS Amplifier (without Source Resistance)
9:00 Small Signal Analysis of CS Amplifier (with Source Resistance)
15:50 Solved Example
MOSFET - Common Source Amplifier
The common Source is one of the most popular amplifier configurations of the MOSFET.
For the AC signal, since the source is common between the input and the output side, it is known as the Common Source Amplifier configuration.
In this video, the small-signal analysis of the Common Source Amplifier is explained with and without the presence of the source resistor. And in both configurations, the MOSFET was biased with voltage divider bias. And at the later part of the video, one example is also solved.
The link for the other useful videos related to MOSFET:
1) Enhancement Type MOSFET:
• MOSFET - Enhancement T...
2) MOSFET Biasing: Enhancement Type MOSFET Biasing Explained
• MOSFET Biasing : Enhan...
3) MOSFET Channel Length Modulation
• MOSFET- Channel Length...
4) MOSFET Small Signal Model:
• MOSFET Transconductanc...
This video is helpful to all the students of science and engineering for understanding the small-signal analysis of the Common Source MOSFET amplifier.
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#MOSFET
#MOSFETAmplifier
#MOSAmplifier
#CommonSourceAmplifier
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[@ALLABOUTELECTRONICS]

Timestamps for the different topics covered in the video: 0:00 Introduction 1:56 Small Signal Analysis of CS Amplifier (without Source Resistance) 9:00 Small Signal Analysis of CS Amplifier (with Source Resistance) 15:50 Solved Example

[@user-nl4ry3wb1x]

0:43 - 0:51 so ,in this configuration ,the small input signal is applied between the gate and the source terminal.在common source組態裡，輸入的小訊號會從 gate terminal到source terminal 0:51 - 0:55 while the output is measured between the drain and the source terminal. 0:55 - 1:02 that means as far as the AC signal is concerned ,then the source terminal is common between the input and the output side. 就ac訊號而言，在輸入端和輸出端都會用到 source terminal 2:51-3:11 That means to perform the AC analysis of any 1.consider all the dc sources in the circuit as zero 2:58-3:02 2.replace all the coupling and bypass capacitors by short circuit 3:02-3:07 3.replace the mosfet by the small signal model 3:07-3:11 4:39 - 4:50 we can say that this input impedance is equal to Vin/Iin=(R1 || R2) 5:04 - 5:10 so,to achieve the high input impedance ,the value of this R1 and R2 should be very high. 6:21-6:25 the ouput is measured between the drain and the source terminal. 6:26 - 6:36 and since this drain current ID is flowing in this anti-clockwise direction ,so we can say that this Vo is equal to -ID*RD. 6:36-6:42 Vo is equal to -ID*RD=-gm*VGS*RD

[@kwekker]

my man I think you just saved my grade. thank u so much

[@Tristan-mc4wm]

haha lekker jochem

[@SilentHacks-ii4qc]

BEST VIDEO , HONESLTY TOP NOTCH. CLEAR VOICE AND EASY TO UNDERSTAND . Good Job.

[@dr.vandanakhanna8813]

Very nicely explained. Great job!

[@Skylife333]

amazing, way better than my coures professor

[@rutwikmore7462]

Explained in very easy way😊. Thank you!!!!

[@mayurshah9131]

EXCELLENT 👍 HEARTLY CONGRATULATIONS AND ALL THE BEST FOR 300K

[@gss8594]

thank you for clear explaination

[@kyriakoskane233]

Great job thank you

[@easywaysgyaan1376]

Got it so correctly only because of you ..... Thank you sir ♥️

[@mdalmamun6562]

It’s awesome. Thank you 😊

[@user-yr4jk5oh3t]

9:56 Could u possibly answer my question? Here, I understand output coupling capacitor or input coupling capacitor can be short circuited. But how about capacitor placed between output(drain) to GND? Could u tell me if Such capacitor can also be shorted? I usually see such kind of problems on my old textbook. I might just don’t understand how capacitor should be treated in small signal circuit on a more general circuit. Eg) two resistor R and R’ are connected btw Vdd and drain and the output sensed at drain terminal and there is a capacitor placed btwGND and the point between R and R’.

[@murraychen9436]

Just want to know the analysis for the same circuit but having signal resource resistance Rsig, rd (or ro) parallel to gm Vgs, and unpassed RS.

[@noorsohail1403]

U are the bestttt dudeeeee....❤🌺

[@TechnicallyExplained]

Congratulations on 300k subscribers...may you have 400k subscribers within weeks..

[@shashikantsheoran7312]

At the end of numerical, while calculating voltage gain Av should we consider the value of source resistance i.e. Av=-gm.Rd/(1+gm.Rs)?

[@ALLABOUTELECTRONICS]

When the source resistor is not bypassed then only you should consider that equation for voltage gain. If there is a bypass capacitor across the source resistor then it will not appear in the AC analysis. I hope, it will clear your doubt.

[@bruhbruh4137]

last question why didnt you consider the resistance in source while calculating vout??

[@aamir99204]

sir can u please explain why current ID cannot be 5.62 ma

[@Harshavardhan-zr2ip]

Sir please complete all biasing of JFET and MOSFET

[@lehieu665]

i have a question at 7:44. Are there any other solutions to increase voltage gain but not limit the output swing ?

[@kgy8088]

perfect

[@studyelectronics3995]

Fabulous👏🏻

[@zackarywang1152]

Thanks. What type of MOSFET we are analyzing in the last example? is it a n-channel depletion type MOSFET? should the Vt be negative or positive?

[@ALLABOUTELECTRONICS]

It is n-channel MOSFET. And threshold voltage is positive of n-channel MOSFET.

[@zackarywang1152]

@@ALLABOUTELECTRONICS Thanks Boss. Another dump question, is this a depletion type n-channel MOSFET working in the enhancement region?

[@haoyuan92]

@@zackarywang1152 Doesn't matter because depletion and enhancement mode only determine whether it is normally on (depletion) or normally off (enhancement).

[@ECEVINCENTKUMARL]

Super

[@bruhbruh4137]

WHY DIDNT YOU CONSIDER R1 AND R2 while calculating vin?? plsssssssssssssssssssss tell i am confusedddddddd

[@sahilthakur279]

Can we use gm=id/vgs for calculating gm because then the value of vgs is totally different

[@leppuofficial3675]

on 18:39 why 5.62mA not operation in saturation region.. how to recognize it? thank you

[@ALLABOUTELECTRONICS]

In that case, if you calculate the Vgs then it is 6V - (1.2) (5.62) = -0.7V. Since Vgs is negative, the N-type MOSFET will operate in the cut-off region. Because for MOSFET to turn on, Vgs should be greater than Vt. I hope it will clear your doubt.

[@leppuofficial3675]

@@ALLABOUTELECTRONICS thank you.. all clear sir

[@kwekker]

the quality of this video is super high too, wow

[@प्रणव_गुप्ता]

Sir please explain at 18:26 how will solve that quadratic equation in exam it's coefficients values is very large?

[@ALLABOUTELECTRONICS]

You can use scientific calculator for solving the quadratic equations.

[@GrindOne69]

Dear Sir, @19:19 duration, can't we use formula gm=Id/Vgs?

[@ALLABOUTELECTRONICS]

You can use that formula, if you know small signal drain current Id (NOT DC drain current) and small signal voltage across gate and source. (Vgs). Practically, if you want to find the transconductance of the MOSFET, then by measuring id and Vgs, you can find that. Here while solving example, since do not know, these values, so we have used other equations of the transconductance.

[@aashman_40k]

Where did Rs go in the Small signal model of the solved example? Will it's inclusion change the values of Zin and Zout?

[@ALLABOUTELECTRONICS]

Becuase of the bypass capacitor, it will get short circuited in the small-signal analysis. Before the example, I have already shown the expression of input and output impedance with Rs. Please go through the chapters (timestamps) given in the video. You will get it.

[@dorukilhan4329]

so everything is same with bjt's besides K formula ?

[@mainakseal5027]

lovely explanation...loved it

[@pierpa_76pierpaolo]

How many times is it able to amplify a sound, noise or music ? How many times? I need an 'audio amplifier with an output of No. 1000 times. I have seen simple dividers with mosfets but they only multiply by 12 times. How to proceed? I am waiting in anticipation. Thank you very much.

[@arnab94mallick]

Could you please make some good videos on EM theory specially concentrated on Antenna Theory..

[@arnab94mallick]

It will be of immense help for us.

[@ALLABOUTELECTRONICS]

Yes, once I finish the series on MOSFET, I will definitely consider it.

[@maituyetlan614]

Hey teacher, do you have video about AC analysis Mosfet ?

[@ALLABOUTELECTRONICS]

Yes, please check this video: kzbin.info/www/bejne/q6Wlg4qBaaygo6c For more info, please check the JFET and MOSFET playlist on the channel.

[@bagavat21520]

How to find the value of c1 and c2 and c3 here

[@lordgamingyt9405]

Sir please upload concepts of vlsi

[@bruhbruh4137]

@7:09 isn't Vgs=(R1||R2)Vin

[@blake632]

If there is ro resistance and Rs resistance, I cannot find how to find Zo. You have not added ro at all.

[@MaheshKumar-sx7oj]

Sir if u can provide notes of what ever you have written it will be more useful for us sir

[@ALLABOUTELECTRONICS]

The notes have been uploaded on the website. Here is the link for some of the MOSFET related notes. www.allaboutelectronics.org/mosfet-tutorials/

[@aravindh06]

lot of thanks , i have one doubt why we take 1.11mA not 5.62mA

[@ALLABOUTELECTRONICS]

If you use Id = 5.62 mA, then VGS will become negative. (Because here VGS = 6 - IDRs). If VGS is negative, then MOSFET is in cut-off region. And hence, the circuit will not operate. And That's why second value of Id (1.11 mA) is chosen. I hope, it will clear your doubt.

[@sunitsawant885]

16:15 i have been given rd =40K ohm how will it affect the Ac analysis diagram and values?

[@ALLABOUTELECTRONICS]

How about the source resistor? Is it the same or different? First using DC analysis, you need to find the value of gm (transconductance). And then using the formula, or using AC analysis, you can find input, output impedance and gain.

[@sunitsawant885]

@@ALLABOUTELECTRONICS I found my answer and thank you soo much for the much needed explanation... Truly good.

[@bruhbruh4137]

@19:00 I HAVE A DOUBT AS TO VERIFY THE VALUE OF ID ?? HOW?? WH DIDNT WE TAKE 5.11 ??? HOW TO CHECK WHETHER THE VALUE OF ID is not valid for given case???

[@ALLABOUTELECTRONICS]

Vgs= 6V -Id *Rs, where Rs = 1.2 K. If we select the value of Id as 5.62 mA, then Vgs will be negative. It means with that value of Id, MOSFET is off, which is not possible. That is why that cannot be the value of ID. I hope, it will clear your doubt.

[@tompang5296]

19:20 Why is there a 2 in front of the k? The other times I’ve encountered this formula there’s no 2 there…

[@ALLABOUTELECTRONICS]

The MOSFET transconductance gm = un Cox (w/L) ( Vgs - Vt) Where, K = 1/2 un Cox ( w/L) That is why there is 2. I hope, it will clear your doubt. For more information, please check the video on MOSFET transconductance. Here is the link : kzbin.info/www/bejne/q6Wlg4qBaaygo6c

[@dylanzheng2551]

I think at 17:32 in the saturation Id=1/2 * k (V_G- V_T)^2 is this right？

[@ALLABOUTELECTRONICS]

Yes, in saturation, Id = 1/2 µn Cox (W/L) (Vgs - Vt)^2 Here, 1/2 µn Cox (W/L) is considered as constant. And that is why the equation is written as K (Vgs - Vt)^2

[@dylanzheng2551]

@@ALLABOUTELECTRONICS Thank you so much!! That is really helpful!!

[@sachinkumarraghuvanshi5069]

what about 30v terminal voltage ,you have considered it no where?

[@ALLABOUTELECTRONICS]

Would you please mention the timestamp, where you are referring to ??

[@vedant6029]

isn't the formula of gm=k*(Vgs-Vt)....where k=unCox*(w/l)?...why have you taken an extra factor of 2 @ 19:42 ?

[@ALLABOUTELECTRONICS]

Id = 1/2 (un Cox) (W/L) (Vgs - Vt^2. Or K = 1/2 (unCox)(W/L) Therefore, Id = K (Vgs - Vt)^2 That means gm = ∂Id / ∂Vgs = 2 *K * (Vgs - Vt) I hope it will clear your doubt.

[@rajeshwar2109]

@@ALLABOUTELECTRONICS thank you very much

[@Vishal_Gwall]

I'm second Because Everyone is first 🙃

[@pakeru1768]

I have question. Why we don't use the Id1 value?

[@ALLABOUTELECTRONICS]

Would you please mention the time where you are referring in the video ? It would be easy for me to answer your question.

[@abubakarsiddiq7271]

is it p-channel or n-channel mosfet? if n-channel , what about p-channel. And if finite output impedance (r0) then calculation what?(unbypass Rs)

[@ALLABOUTELECTRONICS]

On the channel, if you see MOSFET playlist, you will also find p- channel MOSFET example. Please check that playlist. Most of your doubts will get clear. If you still have any doubts, then let me know here.

[@abubakarsiddiq7271]

@@ALLABOUTELECTRONICS I Want to learn p channel MOSFET gain(Av) and Output impedance(Z0) derivation, with internal resistance (small rd),,but here I could not find this.

[@pramya7535]

Voltage gain when rs is not bypassed is -1. 690

[@nidhiashok9940]

Why did u take gm=2k(Vgs-Vth)?, shouldn't it be k(Vgs-Vth)?

[@ALLABOUTELECTRONICS]

The drain current Id = 1/2 (μnCox) (W/L) (Vgs - Vt)^2 Or Id = 1/2 (kn) (Vgs - Vt)^2 Where Kn = (μnCox) (W/L) So, after differentiating the above expression, we are getting gm = kn (Vgs - Vt). But here in the question we have been given constant K (not Kn) Where K is the device constant. And it is equal to 1/2 (μnCox) (W/L). So, based on that, here we are getting gm = 2K (Vgs - Vt) I hope, it will clear your doubt.

[@besmartknowledgeable]

Hi there

[@Ritik-ww7ro]

For BCEIAN go from 12:00

[@gulamashrafshaikh445]

18:45 why I1 is not the value?

[@ALLABOUTELECTRONICS]

With that value, the Vgs will be negative. And in that case, the MOSFET will not conduct. You can put that value in Vgs equation and check. I hope, it will clear your doubt.

[@gulamashrafshaikh445]

@@ALLABOUTELECTRONICS yes, thankyou basically Vgs must be greater than Vth for on MOSFET.

[@wongyithong9838]

All prayers for the India family.

[@GrindOne69]

Sir, what is Ro?

[@ALLABOUTELECTRONICS]

It is the output impedance.

[@GrindOne69]

@@ALLABOUTELECTRONICS output impedance as in external output impedance or the drain resistance?

[@ALLABOUTELECTRONICS]

@@GrindOne69 It is the output impedance of the MOSFET. (Because of the channel length modulation).

[@Avinashkumar-op4ex]

what indicate gm sir?

[@ALLABOUTELECTRONICS]

It is the transconductance of the MOSFET. I have made a separate video on it and have explained it in detail. Here is the link: kzbin.info/www/bejne/q6Wlg4qBaaygo6c

[@SuperPaul5000]

How can i calculate r0?

[@ALLABOUTELECTRONICS]

From the channel length modulation parameter (lamda) or Early Voltage Va, the Ro can be calculated. If you go through the video on channel length modulation in MOSFET, I have explained there. Moreover, you can also refer the JFET and MOSFET playlist for more solved examples. In some examples, the output resistance is calculated using early voltage or lamda.

[@sivaprasadnakka6010]

Previous video link send me

[@ALLABOUTELECTRONICS]

It is already given in the description of the video. ( Small signal model) But anyways, here is the link : kzbin.info/www/bejne/q6Wlg4qBaaygo6c

[@kashishkarera7762]

Why was Id1 ignored??

[@ALLABOUTELECTRONICS]

Would you please mention the timestamp where you are referring to in the video?

[@nthumara6288]

what is gm

[@ALLABOUTELECTRONICS]

It is a Transconductance of the MOSFET. I have already made a seperate video on that. Please check this link : kzbin.info/www/bejne/q6Wlg4qBaaygo6c

[@ajayajju5802]

First view

[@vlog85773]

Hello sir please Hindi language

[@asthagupta6433]

bhai kuch smajh nai aata hai presentation ki tarah bna ke khatam kr dete ho yr or wo same pitch pe pura video chlta rehta hai

[@sourcecreator2222]

please no more with this music...

[@zoro.mf69]

Very well explained