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Does the threshold of the transistor vary with fingers?

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iVenky

iVenky

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Does the threshold voltage of MOS transistors vary with fingers?

Hi,

I would like to know if the threshold voltage of MOS transistors vary with the number of fingers in these advanced technologies. I mean compared to multipliers, does the threshold vary?

Thanks!
 
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Yes. Layout dependent effects (LDE) can effect the Vt of transistors. I have also seen Vt vary depending on the device W but that was on a special type of mosfet.
 

Re: Does the threshold voltage of MOS transistors vary with fingers?

iVenky said:
I would like to know if the threshold voltage of MOS transistors vary with the number of fingers in these advanced technologies. I mean compared to multipliers, does the threshold vary?!
Click to expand...

I do not know the answer but the role of the fingers is to apply the electric field uniformly over a larger area and (at the same time) reduce the effective area so that the effective capacitance is reduced. The threshold voltage will not be dependent on the number of fingers (at least to the first order)- that depends on the manufacturing process.
 
I think threshold voltage variation of transistors with the number of fingers is an artefact: threshold voltage is given for a distinct operation point (OP) of Vds and Id. Realizations of the same transistor (re. width & length) with different number of fingers in layout usually create different source and drain voltage drops (from Id via Rs & Rd), and different (internal) Vsb and Vdb voltages. So for the same Vds & Id OP, (external) Vth may be a little bit different.

Any analog circuit in advanced technologies, also analog multipliers suffer from such a layout artefact, I believe.
 
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