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for help on convergence issue when run pss simualtion (Read 1616 times)
hiSkill_11
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for help on convergence issue when run pss simualtion
Jan 06th, 2016, 1:21am
 
Hi Guys,

I am running pss+pnoise on crystal oscillator and encounter a convergence issue as following. The strang thing is that when I run the same circuit at 125deg the pss completed as expected, but fail at -40deg. I am not sure about whether it is caused by circuit or model or simulator. Any comments would be very appreciated.

*****************
DC Analysis `dcOp'
******************
Important parameter values:
   reltol = 1e-06
   abstol(V) = 1 uV
   abstol(I) = 1 pA
   abstol(Temp) = 100 uC
   abstol(Pwr) = 1 nW
   temp = -40 C
   tnom = 25 C
   tempeffects = all
   gmindc = 1 pS
   rabsshort = 1 mOhm
Trying `homotopy = gmin'.

Notice from spectre during DC analysis `dcOp'.
   GminDC = 1 pS is large enough to noticeably affect the DC solution.
       dV(I0.I1.op1) = -47.3664 uV
       Use the `gmin_check' option to eliminate or expand this report.

Convergence achieved in 148 iterations.
Total time required for dc analysis `dcOp': CPU = 2.37064 s, elapsed = 937.469 ms.
Time accumulated: CPU = 4.24635 s, elapsed = 32.2662 s.
Peak resident memory used = 91.8 Mbytes.

dcOpInfo: writing operating point information to rawfile.

*****************************************************************
Periodic Steady-State Analysis `pss': estimated fund = 24.012 MHz
*****************************************************************
Trying `homotopy = gmin' for initial conditions.

Notice from spectre during IC analysis, during periodic steady state analysis `pss'.
   GminDC = 1 pS is large enough to noticeably affect the DC solution.
       dV(I0.I1.op1) = -47.3664 uV
       Use the `gmin_check' option to eliminate or expand this report.

DC simulation time: CPU = 2.08568 s, elapsed = 542.645 ms.

MultiThread info: 7 new work threads created

Using linear IC

Warning from spectre during periodic steady state analysis `pss'.
   WARNING (CMI-2139): I0.I0.N2.qsnap: The base-emitter junction current exceeds `imelt'.  The results computed by Virtuoso(R) Spectre are now incorrect because the junction current model has been linearized.
   WARNING (CMI-2363): I0.I0.N2.qsnap: `ic' exceeds `imax1'.
Notice from spectre during periodic steady state analysis `pss'.
   I0.I0.N2.qsnap: The base-emitter junction leaves the linearized region.
   I0.I0.N2.qsnap: `ic' returns to normal.
Warning from spectre during periodic steady state analysis `pss'.
   WARNING (CMI-2139): I0.I0.N2.qsnap: The base-emitter junction current exceeds `imelt'.  The results computed by Virtuoso(R) Spectre are now incorrect because the junction current model has been linearized.
Notice from spectre during periodic steady state analysis `pss'.
   I0.I0.N2.qsnap: The base-emitter junction leaves the linearized region.

Linear IC: estimated frequency is 2.24101e+07 Hz

=================================
`pss': time = (0 s -> 2.25781 us)
=================================

Output and IC/nodeset summary:
                save   4       (current)
                save   20      (voltage)

Important parameter values in tstab integration:
   start = 0 s
   outputstart = 0 s
   stop = 2.25781 us
   period = 44.6228 ns
   maxperiods = 50
   step = 2.12394 ns
   maxstep = 100 ps
   ic = all
   useprevic = no
   skipdc = no
   reltol = 1e-06
   abstol(V) = 1 uV
   abstol(I) = 1 pA
   abstol(Temp) = 100 uC
   abstol(Pwr) = 1 nW
   temp = -40 C
   tnom = 25 C
   tempeffects = all
   method = trap
   lteratio = 3.5
   relref = sigglobal
   cmin = 1 fF
   gmin = 1 pS
   rabsshort = 1 mOhm

Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.
Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.
Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.
Zero diagonal found in Jacobian at `V1:p' and `V1:p'.
Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.

Error found by spectre at time = 3.2 ns during periodic steady state analysis `pss'.
   ERROR (SPECTRE-16192): No convergence achieved with the minimum time step specified.  Last acceptable solution computed at 0 s.

The values for those nodes that did not converge on the last Newton iteration are given below.  The manner in which the convergence criteria were not satisfied is also given.
           Failed test: | Value | > RelTol*Ref + AbsTol

Top 10 Solution too large Convergence failure:
   I(V4:p) = 29.3536 uA, previously 29.3536 uA.
       update too large:  | -248.147 pA | > 29.3536 pA + 1 pA
   I(V0:p) = -13.0754 uA, previously -13.0754 uA.
       update too large:  | -83.4838 pA | > 13.0754 pA + 1 pA
   V(I0.I1.net0135) = -19.1005 V, previously -19.1005 V.
       update too large:  | 45.267 uV | > 19.1005 uV + 1 uV
   I(V1:p) = -1.73303 mA, previously -1.73303 mA.
       update too large:  | 3.40771 nA | > 1.73303 nA + 1 pA
Top 10 Residue too large Convergence failure:
   V(I0.I1.C9.11) = 120.642 pV, previously 120.642 pV.
       residue too large: | 50 pA | > 151.123 aA + 1 pA
   V(I0.I1.C0.11) = 166.275 uV, previously 166.275 uV.
       residue too large: | 24.7732 pA | > 74.3217 aA + 1 pA
   V(I0.I0.I0.C1.11) = -14.6418 uV, previously -14.6418 uV.
       residue too large: | 12.1248 pA | > 36.3785 aA + 1 pA
   V(vclk) = 3.73789 nV, previously 3.73789 nV.
       residue too large: | 8 pA | > 181.01 aA + 1 pA
   V(I0.I1.C19.11) = 22.1314 uV, previously 22.1314 uV.
       residue too large: | 7.37346 pA | > 22.1317 aA + 1 pA
   V(I0.I1.C19.1) = 731.648 mV, previously 731.648 mV.
       residue too large
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Geoffrey_Coram
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Re: for help on convergence issue when run pss simualtion
Reply #1 - Mar 16th, 2016, 10:10am
 
Quote:
Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.

What's connected to I0.I1.on ?  How do those devices look at -40?

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hiSkill_11
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Re: for help on convergence issue when run pss simualtion
Reply #2 - Mar 16th, 2016, 11:59pm
 
Hi Geoffrey_Coram,

Many thanks for your help.

I attached the schematic part for you.


Geoffrey_Coram wrote on Mar 16th, 2016, 10:10am:
Quote:
Zero diagonal found in Jacobian at `I0.I1.on' and `I0.I1.on'.

What's connected to I0.I1.on ?  How do those devices look at -40?


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fig_pss.png
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Shawn Wang
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Re: for help on convergence issue when run pss simualtion
Reply #3 - Jan 7th, 2018, 11:39pm
 
hi,  hiSkill_11

Do you solve this problem? I encounter the same problem during PSS analysis. The tran simulation is ok, but PSS fails.

If you have the solution, could you share with me?

thanks
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Ken Kundert
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Silicon Valley
Re: for help on convergence issue when run pss simualtion
Reply #4 - Jan 8th, 2018, 10:17am
 
This appears to be a transient analysis problem rather than a PSS problem as it is occurring during the initial transient run.

I recommend that you run with the default tolerances.

-Ken
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