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Anyone knows about how much variable capacitance is present under how much control voltage for device 'nmoscap'?

Alex Liao

Hi,

I noticed the description for device 'nmoscap' is NMOS in N-Well varactor and there are two fields:

CapValue_(F): variable_a F

CapValue@0V_(F):  variable_b F

It appears clear that variable_b means under the bias voltage (Vgs; S and D are short connected), the Capacitance(Cgs) is this variable_b value. What does variable_a mean? Is it any voltage else will result in a variable_a capacitance or the maximum capacitance under the maximum voltage for a certain W/L it can present? I believe the latter case is true but not quite sure because the maximum is what? Vdd?. Vdd is different in different technology, how to determine which exact capacitance will be for different Vdd?

Also I have searched technology documentation and other related pdf files in the PDK, not much saying on nmoscap. There is one mos varactor, but with size scaling from 0.4u-3.2u for W and 0.4u-2u for L instead of the device that I am caring about which is from 50u to 50um for both W and L. It looks I cannot find any documentation of this device 'nmoscap'. Any idea?

Thanks,

Alex

  • Andrew Beckett

    Alex,

    Your best bet is to ask the foundry or whoever the PDK came from. You didn't mention which PDK is being used, so I doubt anyone would be able to help you without some specific details.

    Regards,

    Andrew.

  • Alex Liao

    Hi Andrew,

    PDK: tsmc90nm- CRN90G

    The version is T_N90_CM_SP_013_V1.1.

    In case someone by chance used this and can provide some knowledge on this matter.

    I will keep asking the PDK provider and see what's happened.

    Thanks,

    Alex

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