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Which Vt to use for calculations?

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mouzid

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What Vt to use?

Hi edaboarders,

I'm using the following techology file:
**broken link removed**
I looked for Vt to do some calculations but I find only VTH0.
Have I to consider Vt=VTH0 ?
 

What Vt to use?

VT0 should work the best with the simple MOS square-law calculation;
that's its purpose.
 

    M

    mouzid

    Points: 2
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What Vt to use?

Do you mean I have to use VTH0 instead of Vgs-Vt in equations ?
Could you provide an exemple ?
 

What Vt to use?

No, VT0 is the "VT" in the Id=u0*Cox*W/L*(Vgs-VT)**2 equation.
 

    M

    mouzid

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Re: What Vt to use?

I'm confused with that. To calculate a pmos pull-up resistor Ron I found two non quadratic equations:

The first:
Ron = 1/[u.Cox(W/L).(Vgs-Vt)]

The second is
Ron = 1/[u.Cox(W/L).(Vgs-Vt-Vds)]

1- Is VT=VT0 also valid ?
2- Which is the best relation of Ron to use with that assumption the first or the second equation ?
 

Re: What Vt to use?

1. VT0 is the threshold with zero body source voltage and at nominal temperature.
2. If you do the math (just find the derivative of MOS equation in linear region!), the 2nd form is the more accurate one. However, it is troublesome to use due to the dependence on Vds. Which equation to use depends on whether you foresee your vds to be comparable to the overdrive.
 

Re: What Vt to use?

vth0 is the normal threshold votlage with zero body to source potential difference
 

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