MOSFET Biasing : Enhancement Type MOSFET Biasing Explained
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- Опубліковано 22 лип 2024
- In this video, the biasing of the Enhancement Type MOSFET is explained and the different biasing configurations like Fixed Bias, Voltage Divider Bias, Drain Feedback Bias, and Constant current Biasing is explained.
By watching this video, you will learn the following topics:
0:00 Introduction
0:37 The need for Biasing in MOSFET Amplifier
3:56 Fixed Bias Configuration
9:56 Voltage Divider Bias
14:47 Drain Feedback Bias
16:21 Constant Current Biasing
The need for Biasing in MOSFET Amplifier:
To use the MOSFET as an amplifier, it needs to be operated in the saturation region where the MOSFET operates as a voltage-controlled current source.
To ensure the operation of the MOSFET in the saturation region, and to get linear amplification, MOSFET needs to be biased properly.
MOSFET Biasing Configurations:
There are several ways to bias the MOSFET.
But the following are the most common biasing configurations
1) Fixed Bias
2) Voltage Divider Bias
3) Drain Feedback Bias
4) Constant Current Bias
The Fixed Bias Configuration is the most simple biasing technique, but in this configuration, the operating point is more susceptible to the change in the external parameters and MOSFET parameters.
The Voltage Divider Bias and Drain Feedback Bias stabilize the operating point to some extent.
The constant current Biasing configuration is a more robust biasing configuration and prevents the change in the operating point due to external parameters. Typically it is used in the integrated circuit for the MOS amplifier.
In this video, different biasing configuration, as well as the DC analysis of the different biasing configurations, is explained.
This video will be helpful to all the students of science and engineering in understanding the different MOSFET biasing configuration.
The link for the other useful videos related to MOSFET:
1) Enhancement Tye MOSFET Explained
• MOSFET - Enhancement T...
2) Depletion Type MOSFET Explained
• MOSFET- Depletion Type...
3) Depletion Type MOSFET Biasing Explained
• MOSFET Biasing: Deplet...
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Timestamps for the different topics covered in the video:
0:00 Introduction
0:37 The need for Biasing in MOSFET Amplifier
3:56 Fixed Bias Configuration
9:56 Voltage Divider Bias
14:47 Drain Feedback Bias
16:21 Constant Current Biasing
0:25 why we need to bias the MOSFET
0:39 we want to use the MOSFET as an amplifier 我們要把 MOSFET當成一個放大器
0:42 that means whenever we apply a small input to hte MOSFET ,then we should get the amplifier output signal
照理講，這個用MOSFET做成的放大器，如果輸入一個小訊號，應該要給我們一個把該訊號放大之後的訊號
0:49 - 0:59
But if we just apply a small input signal between the gate and the source then we directly can not get the amplifier output.And that is because of the MOSFET characteristics . 但實際上如果我們給MOSFET一個小訊號，他不會給我們一個放大的訊號，這點我們可以從MOSFET的I-V特性圖 看出來
1:01 - 1:09
if you see the transfer characteristic of the enhancement type MOSFET,then it starts conducting when the voltage VGS is greater than the threshold voltage
1:10-1:19
That means whenever we directly apply a small input signal of a few mV between the gate and the source terminal then the MOSFET will not get turned ON.這意味著當我們直接給一個大約只有幾 mV 的電壓給 gate 和 source , then MOSFET就不會打開
1:19-1:24
That means there has to have some DC biasing voltage which is greater than the threshold.這意味著 必須用一些 大於門檻電壓的 直流偏壓電壓
（意思就是說加一個大於門檻電壓的直流偏壓電壓來解決MOSFET無法啟動的問題）
1:48 - 1:56
whenever we want to use the MOSFET as an amplifier, then it needs to be operated in the saturation region
1:56 because in this saturation region the drain current remain constant
2:09-2:15
That means by controlling the voltage VGS ,the drain current can be controlled
3:48 - 3:55
Now,the easiest way to bias this MOSFET is by applying a fixed voltage between this gate and the source terminal.
3:57 - 4:05
so,here,since this gate current IG is approximately equal to zero(因為 G terminal 絕緣) 所以在Rg上面幾乎沒有壓降
4:05 - 4:11
that means in this case,the voltage VGS is equal to VGG
4:11 - 4:17
and on top of it , a small input signal can be applied through this coupling capacitor.
4:17 - 4:22
but for the dc analysis ,this coupling capacitor will act as an open circuit.(電容對直流來說是斷路，電容對交流來說是短路)
注意：open circuit是斷路
6:43 - 6:55
in the graph ,the yellow line means load line.That means whenever this voltage VDS is equal to zero,then the drain current ID is equal to VDD/RD
6:56 - 7:02
And whenever this ID is equal to zero ,then the voltage VDS is equal to VDD.（由圖中看出來的）
8:33 - 8:42
now,although this fixed bias is a very simple biasing technique ,it is not a good approach to bias the MOSFET.
8:42-8:50
the reason is ,in this configuration ,the biasing poit is very susceptible to the change in the temperature as well as the other MOSFET parameters.因為在這種組態，biasing point 非常容易受到溫度影響，因為溫度會影響 MOSFET的常數
8:51 - 9:00
For example,this mobility and the threshold voltage are temperature dependent.
(意思就是溫度一旦變化，參數都會變化，所以ID也會跟著變化)
9:46-9:51
That means in terms of the biasing stability ,this fixed bias is not an ideal biasing technique.
9:51- 9:56
and this biasing stability can be improved using the voltage diveider bias.
10:03 - 10:16
because the IG is approximately equal to 0 ,so the current flow through the R1 and R2. That means using these two resistors ,we can decide the gate voltage.(用分壓定理)
10:24 - 10:34
so here ,the ac input signal is applied using the coupling capacitor.but for the dc analysis ,these coupling capacitors will act as an open circuit.
10:35 - 10:46
VG is equal to [R2/(R2+R1)]*VDD（分壓定理）
10:46 - 10:54
and once we know this gate voltage ,then by applying the KVL（克希荷夫定律） in this loop ,we can find the relationship between VG and the drain current.
11:03 - 11:14
VG-VGS-ID*RS=0(by KVL)
12:04-12:20
VDD-ID*RD-VDS-ID*RS=0(by KVL)
Thank. The teaching about my this in my university sucks so much. Glad that UA-cam University once again saves lives.
Thankyou!! This is a very well organized video 🤍🤍
VERY NICE, PLEASE CONTINUE ,WE ARE ENJOYING YOUR VEDIOS
I was wondering how was the locus of pinch off voltage determined ( Vds = Vgs - Vt ) and this video answered that beautifully! Thank you!
Thank u sir i got so much to learn from this single video
How do I decide or find the biasing current for correctly reaching saturation region. If you can show through a datasheet it will be great for instance Mrf300 ldmos
can you please tell, how to select the resistor for the drain feedback biasing.
very helpful, ty
Thank you so much sir
I have issues that.. mosfets are damage and burn when we send stop command to our device... please tell me solution..
Thank you very much
Thank you so much....
Thank you ❤❤❤
Thanks
At time stamp 16:08 I think the simplified symbol for the enhanced P channel should show the arrow on the lower (source) and point inwards to show current flow direction. Is your diagram correct?
How does D-mosfet can be used as enchancement?
D-mosfet has both depletion mode and enhancement mode but it is called depletion type mosfet...for n-channel depletion type mosfet, when vgs>0V, we have enhancement mode in D-mosfet
Where can I find AC Analysis of voltage-divider-bias circuit using N-channel Enhancement MOSFET?
Please check the MOSFET playlist on the channel. You will find there. In case, if you don’t get it then let me know. I will share the link.
@@ALLABOUTELECTRONICS First of all, thank you for your interest. I found only this video on the list "ua-cam.com/video/vBvLu3euc2Q/v-deo.html" , but it's not exactly what I want. I want to prove Zi, Zo and Av equations with DC and AC analysis for Voltage-Divider Bias Enhancement Type MOSFET.
Please check this playlist:
ua-cam.com/play/PLwjK_iyK4LLC-tRT_Uml3T-ifdcmuykjV.html
You will get it the video.
Thanks but I got confused from minute 13:00, the formula Vgs = Vg - Id * Rs, if Vgs =0 then transistor is OFF, then no current is flowing at Id, therefore how is possible that Id = Vg / Rs. Thanks again
The yellow line, Vgs = Vg - Id*Rs is load line. And does not represent the actual current through the device. The intersection of the load line with the transfer curve will give you the actual current and voltage of the device.
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Can you make a video on MOS capacitor?
Yes, will cover it.
👌👌👌👌👌
Dear sir
I will write gate EC this year and I want to know which branch in MTech is better in terms of placement and also which college is best for that branch?
In terms of the placement, VLSI has better placement. IISC CEDT and IITD VDTT (VLSI Design Tools and Technology) are very good.
@@ALLABOUTELECTRONICS and sir how is the placements of other branches like communication / microwave ??
It is Ok. Usually, it is not as good as VLSI. But it may change with year to year, and depends on the companies which are participating in the placement.
@@ALLABOUTELECTRONICS thankyou so much sir for all this information. One last question sir do branch matters or college matters? For example lower branch in IIT D(old IITs ) or VLSI in NIT TRICHY (south nit's)Which option I should go for??
Is the operating point same as bias point?
Yes, they are same.
@@ALLABOUTELECTRONICSThank you for your quick reply.
WHAT IS VALUE OF µn IN MOSFETS?
μn is the mobility of electron. In silicon, it is around 1000 to 1400 cm^2 / (V.s)
Good work sir..Congratulations in advance on 300k subscribers..you deserve it...BTW I am struggling to reach 2000 subscribers :p
👌👌👌👌👍
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Another video that didn't help me understand practically. It would be great if you could make a practical video explaining mosfets as switch, as a resistor and as an amplifier.
0:37
5:45
hindi me videos banaye plz...
0.04 id