What Can I do if my PEX netlist does not converge in the simulator?

Document created by rick_sedlak on Sep 24, 2012
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[1] Reduce the number of resistors in the design by reducing parasitic via resistors.  If a large number of resistors are being extracted from Via's in the design, try a more aggressive via reduction setting in the following SVRF statement:

     PEX REDUCE VIA RESISTANCE [layer1 layer2]

                {STANDARD [COUNT max] [DISTANCE value] |

                FLEXIBLE [DISTANCE value] [MINSTEP value] |

                MINIMUM |


OFF is least aggressive.  FLEXIBLE is more aggressive.   STANDARD can be made most aggressive





[2] Reduce parasitic elements further by using the Pex Reduce Ticer reduction statement.  Sweep the TICER frequency setting from zero Hz to a reasonably high value to find a frequency at which TICER reduction of parasitic elements is maximum.

[3] Reduce parasitic resistor counts even further using PEX REDUCE MINRES COMBINE threshold.  This combines all unprotected resistors of resistance less than the specified threshold into a neighboring larger resistor, and is applied before PEX REDUCE TICER.  Associated capacitors are split equally between two neighboring resistors. A node is protected if it connects more than two resistors, or connects to a port or a device pin.
[4] Consult this TechNote:  MG579191  on  supportnet.mentor.com
      What settings are most aggressive in reducing parasitics in Calibre xRC netlists?



[5] If your circuit simulator allows this, specify a minimum value for resistors to be simulated.  For example, in the simulation testbench input file under 'simulatorOptions' include a parameter called 'minr'.  You can possibly set this to 0.1 ohm to discard the values smaller than the specified value.


For example: simulatorOptions options reltol=1e-6 vabstol=1e-6 iabstol=1e-6 temp=25 tnom=25 scalem=1.0 scale=1.0 gmin=1e-12 rforce=1 maxnotes=5 maxwarns=5 digits=5 cols=80 pivrel=1e-3 ckptclock=1800 sensfile="../psf/sens.output" checklimitdest=psf minr=0.1


[6] Change the device GATE resistance

        Step Gmin through several orders of magnitude.


[7]  Searching google for convergence problems turns up these helpful documents:


     [7.1]   Solving Spice Convergence Problems

     [7.2]   Step-by-Step procedures help you solve Spice convergence problems

     [7.3]   Correcting Convergence Problems