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question: deviation of Vth

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leonken

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eldo transistor vth

I want to konw the deviation of Vth ( mosfet threshold voltage) for each mosfet in the same process. In the same chip the deviation of same size mosfet is about what? 5% or 10%?
How about the Vth deviation in the same process but in the different die?
thank you
 

eldo meas command

You can refer to the model.
Or the PCM data of the foundry
 

The deviation of Vth is usually below 100mV. But it is very dependent the gate length. You can check the model in details. For short channel device, the Vth deviation is very complicated and is larger than the long channel device.

Yibin.
 

Foundry specs are typically +/- 50mV 3 sigma. This applies to across the wafer and wafer to wafer so no points should be worse than +/- 50mV from nominal. This applies to all transistor sizes but typically only 10um x 10um, 10um x Lmin and Wminx10um is checked. Wmin x Lmin is probably not checked or if it is, the spec may be wider..
The threshold voltage is calculated by ramping Vgs from 0 to 1.8V with Vds = 50mV (or sometimes 100mV). The maximum slope of Ids vs Vgs is calculated and extrapolated back to zero Ids. This zero value IDS is the threshold voltage (Vt0).
 

Hello,

to have this value for MOS you need to take a look on your DRM (Design Rules Manual)
On it you will find the standart deviation (gaussian distribution) of this parameter per type of transistor
 

Vth of each mosfet is a little different from others.
so, how about the difference of threshold voltage between a P channel mosfet and a N channel mosfet.
assume: deltaVth=Vthp -Vthn
The value of deltaVth also vary with chip ?
 

We can check the WAT data form foundry.
But this data is measured after wafer out.
If you use this process first time,You can refer to Spice Model (TT SS FF ...corner) or PCM.
 

If your design kit (models) come from the foundry then they have the statistical variation with them. These variations can be checked using .MEAS command in Eldo. It can be used only with the DC analysis

The syntax is as follows:

.MEAS DC vth0 param='lv9(m)' where m is the MOS transistor identifier

Hope this helps!
 

Or run a parametric sweep first , Goto the 'results browser' and find the transistor and click on vth to plot it. (using Cadence tools that is)
 

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