On May 3, 7:16 am, sykab <sara.cata...@[EMAIL PROTECTED]
> wrote:
> On 2 Maio, 21:30, Riad KACED <riad.ka...@[EMAIL PROTECTED]
> wrote:
>
>
>
> > Ohh Yes I see !
>
> > Is the bulk of your MOS tied to the Source ?
> > If not, your VTH will be strongly impacted by the Body Effect.
>
> > Remember that the VTH equation is roughly given by :
>
> > Vth = Vth0 + Gamma*{sqrt(abs(Vsb-2*PhiFs))-sqrt(abs(2*PhiFs))} with :
> > Vth0 is the Th volltage at Vsb=0 (i,e Vsource tied to Vbulk)
> > Gamma = The body effect factor
> > Vsb = Source to Bulk voltage
> > PhiFS = The Fermi Level stuff ... (never remember the name)
>
> > So if Vsb = 0, then Vth = Vth0 otherwise Vth will be greater.
>
> > You may to take this into account.
>
> > This is a weak point of the NMOS compared to the P-one. Since the Pmos
> > is drawn in an N-well, you can always tie the S-B nodes. But the NMOS
> > is in the global substrate ...
> > This could be solved if you process offers Deep-Nwells that can help
> > in creating isolated Pwells.
>
> > Other parameters like Well Proximity Effects (WPE), Shallow Trench
> > Isolation (STI) Stress ... impact the value of the VTh but it is a
> > third order impact ...
>
> > Look at your MOs model do***entation (MM9, BSIM3, BSIM4 ...) for more
> > details.
>
> > i don't know what you're designing but in a case of diff pair for
> > example, the current is fixed by the current source/mirror, the Diff-
> > pair transistors will then adjust their VGS to match the current fixed
> > by the source. The value of the VGS id of course dependent of your W/L
> > ratio.
>
> > Good luck anyway !
>
> > Riad.
>
> LOL!
> That's what I'm doing, an opamp with a differential pair (to make part
> of a current reference).
> I tied the bulk of all nMOS to ground and the bulk of all pMOS to VCC.
>
> Thanks
Don't know what's your transistor model. In common, BISM model is
always used and you could download the model do***ent to check the
algorithm how to calculate the Vth and Vdsat.
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