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how to varies the threshold voltage for mos transistor??

vishnu4830

hai,

am using cadence virtuoso for my project. Here I got a problem about vth in my ieee base paper they are using high vt and low vt transistors .

In my library I also had low vt and high vt trasistors. But base paper guys are used some low vt at 0.22V for p&n mos high vt 0.466V .

Come to gpdk045 library I have high vt transistors at 0.731V for nmos and 0.6V for pmos low at some 0.4V. So please tell me how reduce the vth in virtuoso?

  • Andrew Beckett

    In the gpdk045 library, each transistor has three variants. There's for example:

    • nmos1v   : "standard" VT
    • nmos1v_lvt : Low VT
    • nmos1v_hvt : High VT

    There are also "native" devices too, and then a 2Volt Standard VT and 2Volt Native device. The same is true for pmos as well.

    So pick the appropriate device and use it in your schematic.

    If you need to change the models you will need to change the models! These are in <GPDKinstDir>/models/spectre . It's a fictional process, so you can do what you like! Probably it would be the vtho (or vth0) parameter in the models.

    Regards,

    Andrew.

  • DeeMJ
    Hai there, I'm dee, also need to use cadence virtuoso for my project. May i know how can I get the gpdk library for the low vt and high vt transistors? Do i have to invoke from the command? Thanks.
  • Andrew Beckett

    If  you're using gpdk045 - which can be downloaded from

    then this has pmos1v, pmos1v_hvt. pmos1v_lvt devices in the library (and similar for nmos). I've no idea what "Do I have to invoke from the command?" means...

    Regards,

    Andrew.

  • DeeMJ

    Thanks, Andrew and sorry for the late reply. This cadence runs using Linux command, so I thought  that I should invoke the gpdk file as I have to invoke the cadence by using the command prompt. So, I just have to download the file and then I could simply use it? Thanks a lot for your help.  

    Sincerely,

    Nurdyana

  • Andrew Beckett

    You need to download the PDK, unpack it using "tar xfz fileName.tar.gz" and then read the reference manual in the doc directory (which is a PDF). This will tell you how to add it to your cds.lib to reference it.

    Andrew

  • DeeMJ

    Hi,

    Thanks for your guide. I'm not very familiar with this and this had been a lot of help. 

    Regards,

    Dee

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