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MOS DC Operating Point

JagdishP

HI,

I am using virtuoso 6.1.5 version. When I chose to print DC Operating Point of the MOSs used in my design, I came across this parameters viz, "Vsat" and "Vdss".

By the values displayed, I was able to figure out that Vsat = Vds- Vdss

where Vds is drain-to-source voltage of selected MOS.

I am not able to understand the significance of this 2 parameters (Vdss and Vsat)

A positive value of Vsat do imply whether the MOS is in saturation region ?

if so then how this value of Vsat is different than Vds-(Vgs_vth) value? 

Can anyone have any idea about what Vsat actually signifies ?

Parents

  • This almost certainly depends on which model you're talking about (you didn't mention which simulator either, so I assume it's spectre). For bsim3v3 and bsim4, there's no operating point parameter called "vsat". There is "vsat_marg" which is vds-vdsat (the parameter vdss appears to be the same as vdsat) - so it's how far within saturation you are. If you look in the Virtuoso Simulator Components and Device Models Reference manual from the MMSIM stream, and look in the bsim4 section (right at the end of the chapter) there are links from the operating point parameters to the equations that define them - there is for vdsat (for vdss there isn't, however, and not for vsat_marg either but it's fairly obvious what it means and this can be checked by simple testing).

    Regards,

    Andrew.

Reply

  • This almost certainly depends on which model you're talking about (you didn't mention which simulator either, so I assume it's spectre). For bsim3v3 and bsim4, there's no operating point parameter called "vsat". There is "vsat_marg" which is vds-vdsat (the parameter vdss appears to be the same as vdsat) - so it's how far within saturation you are. If you look in the Virtuoso Simulator Components and Device Models Reference manual from the MMSIM stream, and look in the bsim4 section (right at the end of the chapter) there are links from the operating point parameters to the equations that define them - there is for vdsat (for vdss there isn't, however, and not for vsat_marg either but it's fairly obvious what it means and this can be checked by simple testing).

    Regards,

    Andrew.

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