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 Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? 

Last post Thu, Jun 19 2014 11:10 AM by XinjiePI. 5 replies.
Started by CadenceUser3 17 Jan 2014 04:55 PM. Topic has 5 replies and 6067 views
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  • Fri, Jan 17 2014 4:55 PM

    Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    Our foundry provides a subcircuit model which produces correct ID-VD and ID-VG curves. However, the .OP vdssat (based on BSIM definition) is wildy different than what is expected, ~200mV higher.

    What I want:

    (1) Custom definition of Vdssat, for example vdssatxxx based on Rout degradation

    (2) Must be able to back-annotate on the schematic

    One way I was thinking is to run a DC sweep, calculate the value vdssatxxx based on my arbitrary definition, and then overwrite the original .dcOpInfo.info file's vdssat with the the calculated value vdssatxxx from the DC sweep. Now, when I back-annotate it should read the .dcOpInfo.info file that was overwritten.

    (1) Is this a reasonable way to do it?

    (2) How do I overwrite the existing dcOPInfo.info file (replace vdssat with an arbitrary value that I have calculated)? Does OCEAN have this feature?

    (3) Is there a better way to have a custom-defined operating point parameter that can be back-annotated?

    • Post Points: 20
  • Sun, Jan 19 2014 2:21 AM

    Re: Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    A couple of options:

    1. Use opParamExprList in the CDF (search in the documentation for this) to allow you to put an expression in the CDF to compute an operating point value from other values.
    2. In IC616 you can use the Annotation Setup form and enter expressions easily to compute other values (for example, to annotate satMargin by using vds-vdsat). 

    You can't really overwrite the dcOpInfo.info file - I'm not sure you'd want to do that anyway.

    It's not that clear precisely how you want to compute the vdsat from a dc sweep, but I doubt you'd really need to use a dc sweep?

    Andrew.

    • Post Points: 35
  • Tue, Jan 21 2014 7:17 PM

    Re: Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    Thanks. I tried #2 listed in your email. It may be the best option. However, it's not easy to come up with an empirical equation for Vdssat based on other operating point parameters (e.g. Vdssat=f(vgs,vds,vth,id,rout,...)). Please let me know if you know of one.

    Ideally, I would like to base Vdssat on a DC sweep of Vds holding Vgs for each transistor at the operating point value. Below are the steps:

    (1) Create original schematic (e.g. an op amp containing 10 transistors) and run .OP sim

    (2) fprint value of Vgs and Vbs using ocean

    (3) Create a new schematic copying only the transistors from original schematic

    (4) Add dc voltage sources to each pin of the transistor in the new schematic using values from step 2 

    (5) Run a DC sweep on Vds (Vgs, Vbs is fixed to operating point value) for the new schematic

    (6) Calculate Rout=deriv(Id) 

    (7) Create arbitrary definition: vdssatxxx is the Vds when Rout is degraded 50% from the value from Vds=Vdd/2

    (8) Take this value of vdssatxxx and annotate on the schematic using schCreateNoteLabel (since I can't overwrite .dcOpInfo.info)

    It's obviously a complicated solution... Please let me know if something like this already exists. I've just started to implement this with Skill and Ocean code (I'm a beginner), so please let me know of any difficulties I may run into.

    Thanks,

    AK 

    • Post Points: 5
  • Mon, Jun 16 2014 5:06 PM

    • XinjiePI
    • Not Ranked
    • Joined on Mon, May 19 2014
    • Posts 8
    • Points 100
    Re: Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    Hi Andrew,

     May I ask some easy questions about opParamExprList expresstion.

    Here I need to calculate res rely on v/i which I can get from OP( mappedRoot(\"A\") \"i\") and OP ( mappedRoot(\"A\") \"v\").

    But somehow I may equals to 0 which I need to add one condition to display inf if this situation happened.

    I try to use the example at document but not working so far.

    Could you please give an simple example that I can follow and study?

    Thanks,

     

    Xinjie 

    • Post Points: 20
  • Tue, Jun 17 2014 9:31 AM

    Re: Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    A little hard to see what you want, but I'd expect something like:

    "if(OP(mappedRoot(\"A\") \"i\")<1e-15 then "inf" else  OP(mappedRoot(\"A\") \"v\")/OP(mappedRoot(\"A\") \"i\"))"

    should do the job.

    Regards,

    Andrew.

    • Post Points: 20
  • Thu, Jun 19 2014 11:10 AM

    • XinjiePI
    • Not Ranked
    • Joined on Mon, May 19 2014
    • Posts 8
    • Points 100
    Re: Custom DC Operating Point Definitions or Overwriting the .dcOpInfo.info file? Reply

    Great help! Thanks Andrew.

     

    Xinjie 

    • Post Points: 5
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Started by CadenceUser3 at 17 Jan 2014 04:55 PM. Topic has 5 replies.