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Simulators >> Circuit Simulators >> Spectre simulation message
https://designers-guide.org/forum/YaBB.pl?num=1170129928

Message started by xwcwc1234 on Jan 29^th, 2007, 8:05pm

Title: Spectre simulation message
Post by xwcwc1234 on Jan 29^th, 2007, 8:05pm

Hi,
I run the Spectre for my circuit , got following mesage:

Warning from spectre during IC analysis, during transient analysis `analysisTran1'.
xt.xi71.xi116.mhp7: Missing bulk-source diode would be forward biased.
xt.xi71.xi116.mhp8: Missing bulk-source diode would be forward biased.
xt.xi71.xi117.mhp7: Missing bulk-source diode would be forward biased.
xt.xi71.xi117.mhp8: Missing bulk-source diode would be forward biased.
xt.xi71.xi128.mhp52: Missing bulk-drain diode would be forward biased.

What is the cause of this message ?

Title: Re: Spectre simulation message
Post by Ken Kundert on Jan 29^th, 2007, 11:46pm

Because of certain the value specified for certain model parameters the bulk-source diode is not modeled, however, if it were it would be forward biased. What this is saying is that you are getting the wrong answer because the bulk-source diode is missing.

-Ken

Title: Re: Spectre simulation message
Post by xwcwc1234 on Jan 31^st, 2007, 7:31pm

Is this problem cause by Spice model ? I use BSIM3v3 for MOS modeling . Is that means the spice model is not correct ?

Title: Re: Spectre simulation message
Post by Geoffrey_Coram on Feb 2^nd, 2007, 5:20am

Since the bulk-source diode is there in any physical mosfet you can manufacture, but it is missing from the spice simulation, then yes, I'd say the spice model has a problem.

It could be that the diode is modeled externally as part of a subckt (the bsim3v3 diode model isn't very sophisticated); you'd have to check that -- and I'd still expect it to turn on and prevent the mos from seeing a forward bias on its b-s junction.