Philosophic question about Mosfet

[sharas]

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]

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]

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]

Guys, tell me something that I don't already know!!

 

[Sceadwian]

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.

 

[yjkwon57]

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~~

 

[tkbits]

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]

Thanks, tkbit.

Your answer is my favourite.

 

[A.Anand Srinivasan]

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]

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...

 

[hermin]

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...