Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Philosophic question about Mosfet

Status
Not open for further replies.

sharas

Member level 4
Joined
Jun 7, 2005
Messages
76
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,965
What enables the ,osfet to amplify???

I know all the equations of the small signal gain etc., but I still don't fully understand what physical phenomena in a transistor enables amlifying an input signal?

The same question is also relevant for the bjt.


I would rally like to read your thoughts on this issue.
 

elec_student

Member level 2
Joined
Nov 21, 2005
Messages
42
Helped
5
Reputation
10
Reaction score
2
Trophy points
1,288
Activity points
1,566
See in a MOSFET on application of a suitable gate voltage, compared to the threshold voltage of MOS, current starts increasing and thus amplification takes place.
 

wchu01

Member level 3
Joined
Nov 23, 2005
Messages
67
Helped
2
Reputation
4
Reaction score
0
Trophy points
1,286
Location
South East Asia
Activity points
1,884
Should the input be at the Gate, which controls the current flowing through the channel from Drain to Source. With an increase in the gate voltage, the channel will be bigger resulting in a larger current drive. From the transistor equation, you will notice that the increase in gate voltage will lead to drain current increase, therefore amplification is possible. That is my take.
 

sharas

Member level 4
Joined
Jun 7, 2005
Messages
76
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,965
Guys, tell me something that I don't already know!!
 

Sceadwian

Full Member level 3
Joined
Sep 25, 2005
Messages
174
Helped
15
Reputation
30
Reaction score
0
Trophy points
1,296
Activity points
3,588
The electric field that is applied to the gate with a carefuly doped and chosen soure/drain silicon layer(s) will cause the electric properties of the properly doped silicon to alter slightly. The real physics behind these interactions are WAY beyond me, but I like to think of it along the lines of the way a human being can 'feel' a static field on something like a Vandegraf generator. Where the applied voltage even at a relativly great distance ends up providing a lot of 'sense' for the materials to react dramatically which produce the amplification. In the case of a Vandegraph generator the applied voltage causes people's hair to stand up on end and repel each other which gives us for a brief time at least a natural sense of strong electric fields. The electron and material interactions in a mosfet or similar device are quiet a bit more complex than that, but it helps me to think of it as a simple static electric field effect, it just effects doped silicon in much more complex ways.
 

    sharas

    points: 2
    Helpful Answer Positive Rating

yjkwon57

Full Member level 4
Joined
Jul 31, 2004
Messages
218
Helped
24
Reputation
48
Reaction score
3
Trophy points
1,298
Activity points
1,808
Hi~~

When MOSFET works in the saturation region, it works like a current source. Then, if you add some resistor to a drain, then, the voltage drop will appear at the drain. If you apply some AC signal as well as a DC level to the gate, the AC component of the drain voltage will appear larger than the AC component of the gate voltage.

Bye~~
 

    sharas

    points: 2
    Helpful Answer Positive Rating

tkbits

Full Member level 5
Joined
Dec 4, 2004
Messages
242
Helped
39
Reputation
78
Reaction score
2
Trophy points
1,298
Activity points
2,209
Amplification uses this principle: a small signal is used to control a large current source.

Amplification does not occur by "growing" or "expanding". It occurs by controlled restriction of a power source.

It's the reason why vacuum tubes are also called "valves".
 

    sharas

    points: 2
    Helpful Answer Positive Rating

sharas

Member level 4
Joined
Jun 7, 2005
Messages
76
Helped
3
Reputation
6
Reaction score
0
Trophy points
1,286
Activity points
1,965
Thanks, tkbit.

Your answer is my favourite.
 

A.Anand Srinivasan

Advanced Member level 5
Joined
Oct 15, 2005
Messages
1,804
Helped
257
Reputation
514
Reaction score
39
Trophy points
1,328
Location
India
Activity points
10,680
Actually the devices amplify the signal just by restricting current and voltages to certain limit based on the input and thereby making the load draw power from the power supplies.
 

nee_naresh04

Member level 2
Joined
Dec 15, 2005
Messages
47
Helped
1
Reputation
2
Reaction score
0
Trophy points
1,286
Activity points
1,657
what i know is the only reason for amplification of any device is DC biasing...we all know that energy cannot be created or distroyed..
so if voltage gets amplified to igh value then current will decrease..this decrease in current and the energy supplied by DC biasing will only cause for amplification...
 

    sharas

    points: 2
    Helpful Answer Positive Rating

hermin

Full Member level 2
Joined
Apr 19, 2005
Messages
132
Helped
12
Reputation
24
Reaction score
3
Trophy points
1,298
Activity points
2,481
Just think that you control the current from source to drain by changing the voltage on the gate. Lets say that the gate voltage changed from 0 to 1 volts, the change in the current on the drain and source will be equal to the gain, so that every small changes on the gate, a large change on the drain to source will correspond to that.

Feel free to correct my understanding...
 
  • Like
Reactions: Nigger

    sharas

    points: 2
    Helpful Answer Positive Rating

    Nigger

    points: 2
    Helpful Answer Positive Rating
Status
Not open for further replies.

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top