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[Moved]: Vdsat in weak inversion - definition

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1091120109

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Reference previous discussion:

https://www.edaboard.com/threads/347253/
Click to expand...

Excuse me, when I simulation my amp,I find vgs-vth=20mv,vdsat=38mv.gain=40dB
1.Does this means the mos is in moderate inversion?
2.vdsat is so small,whether it will have any bad impact on my amp?

thank you very much!
 
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Re: Vdsat in weak inversion - definition

1091120109 said:
1.Does this means the mos is in moderate inversion?
Click to expand...
Yes; moderate or even weak inversion. Depends on the transistor current density Id/W .

1091120109 said:
2.vdsat is so small,whether it will have any bad impact on my amp?
Click to expand...
No, in contrary.
 

Re: Vdsat in weak inversion - definition

Yes; moderate or even weak inversion. Depends on the transistor current density Id/W .
Click to expand...

Could you explain why "weak inversion" here?
According to this, it should be in moderate inversion.

129535d1465020339-inversion.png


Inversion.PNG
 

Re: Vdsat in weak inversion - definition

anhnha said:
Could you explain why "weak inversion" here?
According to this, it should be in moderate inversion.
broken link removed
Click to expand...

According to Binkley (s. below), regarding to the very low vdsat=38mV info (above), it could well be in weak inversion mode. Actually, vdsat shouldn't be lower than 4Vt≈100mV (at room temperature).

log-Ids_vs_Vds_with_inversion_regions.png
 
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Re: Vdsat in weak inversion - definition

erikl said:
According to Binkley (s. below), regarding to the very low vdsat=38mV info (above), it could well be in weak inversion mode. Actually, vdsat shouldn't be lower than 4Vt≈100mV (at room temperature).

View attachment 129547
Click to expand...

What't the disadvantage of Vds< 100mV?
 

Re: Vdsat in weak inversion - definition

shanmei said:
What't the disadvantage of Vds< 100mV?
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Should you mean VDS,sat, there would be none, but theoretically it doesn't seem possible - at least at room temperature or above. But of course VDS,sat depends on its calculation method, i.e. the boundary condition used for it.

Don't mix up the drain-source voltage Vds with the saturation voltage VDS,sat ; Vds may of course be lower than 100mV, it can be zero or even negative - depending on its external circuit.
 
Re: Vdsat in weak inversion - definition

Hi 1091120109

From what I gather from forum posts and discussions with colleagues, (and as erikl said) there is no harm in operating in weak inversion/subthreshold region (also see: https://www.edaboard.com/threads/355783/)
 
Re: Vdsat in weak inversion - definition

anhnha said:
Could you explain why "weak inversion" here?
According to this, it should be in moderate inversion.

broken link removed

View attachment 129535
Click to expand...

Hi anhnha,

Can you please cite the reference from which you obtained that screenshot?
 
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