I'm reading that it acts like it in Saturation, but it's confusing to me since in Saturation there's no slope, rather the curve it's almost a straight line. While in Triode mode there's an upward slope that can serve to amplify the input signal that you put in the gate.

Here are the characteristic curves.

http://macao.communications.museum/images/exhibits/2_10_4_4_eng.png


So my question is... In what region does the MOSFET operates as an amplifier? Thanks in advance.

 

If you want a amplifier you need to work in saturation region. Why?
Because in this region MOSFET work just like a voltage control current source.
Try read this
http://forum.allaboutcircuits.com/showthread.php?p=663195#post663195

 

Correct - there is no (in reality: a slight) slope.
However, please note that you are speaking about the ID=f(VDS) characteristics.
Do you intend to use VDS as input signal to vary ID? No!
The slope you are expecting to verify the amplifying characteristic can be seen in the ID=f(VGS) curve (input-output).
In contrary, the slight slope of the output characteristic curves indicate the desired current output properties of the device (large dynamic resistance).

 

"Do you intend to use VDS as input signal to vary ID? No!"

I just noticed this, thanks for pointing it out it all makes sense now.

Thanks a lot guys, I really appreciate it.

Let's see if what I'm gonna say makes any sense now: Since we never intened to use VDS as input signal, because VGS is the control voltage, which is pretty obvious. We want the MOSFET in Saturation because that's the only mode where VDS value doesn't affect the amplification of the ID signal at all since it's almost exclusively dependant on VGS.
Hence in Saturation, the more VGS we put in the more amplification we'll have. Am I correct?

 

Hence in Saturation, the more VGS we put in the more amplification we'll have. Am I correct?

No - i depends on the MOS type you are using.
The VGS dc value determines the operating point on the Id=f(VGS) curve.
And it is the SLOPE of this curve (at this point) that determines the gain.
For example, a depletion type PMOS transistor provides less gain (smaller slope) for rising positive VGS values (until the device is off for VGS,pinch-off).

 

i see, so if we want to have a higher amplification we have to get an NMOS with a higher threshold votage then?

 

I see, so if we want to have a higher amplification we have to get an NMOS with a higher threshold votage then?

Not necessarily. You want a large transconductance (Gm) which is given in the data sheet.

 

Thanks, looking around I just found the formula the overall gain, so yep it appears we want a large gm to have a large gain:

Av= -Rin/Rin+Rs * gm (RD || RL || ro)

 

Thanks, looking around I just found the formula the overall gain, so yep it appears we want a large gm to have a large gain:

Av= -Rin/Rin+Rs * gm (RD || RL || ro)

Normally, such a formula says nothing - if you don`t explain the meaning of the various symbols. OK - some are self-explaining (like RD perhaps).
Nevertheless, do YOU know the meaning of the symbol ro ?