General doubts about MOSFETs

Akshe said:

Hi,

I have a few doubts about the MOSFETs in general-
1. What is the drain voltage when the MOS is in different modes of operation (saturation,linear and subthreshold). There is a finite current being sourced or sunk by the device and 1 terminal of the device is at Vdd or gnd.

2. In the case of NMOS where we have Vdd at one terminal and Vgate is Vdd too, the voltage at the other terminal can be max Vdd-Vthn. Is this valid only for saturation region operation?
Similarly for the PMOS when there is 0 at Vgate and one of the terminal , the other terminal can have Vthp as the minimum voltage. Is this also valid only for the saturation region?

3. Is this correct-
weak inversion = Subthreshold mode (Vgs<Vth)
Onset of strong inversion = Vgs = Vth
Strong inversion = Linear and Saturation mode

Any good references to help get these answers will also be helpful.:roll:

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Junus2012 said:

Hello

1. the transistor is to be in the saturation region when VGS ≧ Vth and VDS ≧VGS-Vth. Look at the condition AND

the saturation region itself the transistor can be under the strong or the weak inversion (also called subthreshold) depending on the difference value of VGS from Vth. it is assumed ideally that if VGS is less than Vth the transistor will not conduct a current, however, in reality the transistor starts to conduct small amount of current before this Vth, the current is referred as the subthreshold current at the subthreshold voltage . I attached you this image, it will help you.




2. I think you are considering the transistor switch charging a capacitor,;-). yes , it is reffered for the saturation region.

3. exactly right, see also my image

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