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Which region this transistor work in?

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jeepx5

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Hi,
When the Vgs is alittle bit lower than Vth and the Vds is almost zero, Which region dose this transistor work in? The triode or the subthreshold? And in this region, how much is the gds? The spectre shows it works in the subthreshold.


Kinds Regards,

JeepX5
 

definetly the transistor works in subthreshold region
vgs any thing less than Vt it is called subthreshold region
 

Vt is the voltage where you have strong inversion irrespective of the Vds
and hence if the Vgs voltage is less than threshold then the transistor
is definately working in subthreshold region.
 

Hi
gds in subthreshold region is bigger than saturation region.
regards
 

In theory, these answers are vaild, however, in practice you will find that the absolute operation of a transistor near Vt/Vth is more of a grey area than black or white.

When you simulate this transistor, your are probably using a model. The real question is how does this model provide a value for Vt/Vth. In most cases, different companies/foundaries will overspecify the satuaration "Is" current for the transistor turn-on voltage (ie @ VT) roughly between 1e-15 -> 1e-10. In orders of magnitude this is a huge difference ?!?!?

In my experience, you should be concerned with two issues and include some margin. Eg......

for SatMargin use Vds-Vgs+Vt > +/-30mV
but also important is VDSAT = Vgs-Vt > +/-10mV to avoid pinch-off

Hope this provides more depth to your problem
 
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    jeepx5

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    melkord

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awqati said:
In theory, these answers are vaild, however, in practice you will find that the absolute operation of a transistor near Vt/Vth is more of a grey area than black or white.

When you simulate this transistor, your are probably using a model. The real question is how does this model provide a value for Vt/Vth. In most cases, different companies/foundaries will overspecify the satuaration "Is" current for the transistor turn-on voltage (ie @ VT) roughly between 1e-15 -> 1e-10. In orders of magnitude this is a huge difference ?!?!?

In my experience, you should be concerned with two issues and include some margin. Eg......

for SatMargin use Vds-Vgs+Vt > +/-30mV
but also important is VDSAT = Vgs-Vt > +/-10mV to avoid pinch-off

Hope this provides more depth to your problem
Click to expand...

Thank u! U helped!
 

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