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Adding a cap in Ultrasim requires an additional probe statement - any workaround?

ckteng

Hello, I'm adding some caps to nodes in one of my subcircuits by adding a statement with a hierarchical path like this:

C1 Xtop.Xnext.node1 VSS 1e-15

Before adding the cap, I can browse the simulation results using SimVision and see the voltage at node1.

The simulation file includes a probe statement

.probe v(Xtop.*)

After adding the cap the probe seems ineffective and I can't see node1 in my sim results.

If I add a probe statement for node1 specifically I can see it in my results.

.probe v(Xtop.Xnext.node)

I don't want to have to add a probe statement for every node I add a cap to.

Does anyone know why I can't just add the cap and continue to see results?

Thanks!

  • Marc,

    Which version of Ultrasim are you using? This works for me (apologies for the simple circuit - I just threw it together in a text editor!):

    **

    .model nch bsim4 type=n
    .model pch bsim4 type=p

    .SUBCKT BUF y a vdd vss
    MP1 node1 a vdd vdd pch w=1u l=0.2u
    MN1 node1 a vss vss nch w=0.5u l=0.2u
    MP2 y node1 vdd vdd pch w=1u l=0.2u
    MN2 y node1 vss vss nch w=0.5u l=0.2u
    .ENDS BUF

    .SUBCKT MID y a vdd vss
    Xprev mid1 a vdd vss BUF
    Xnext y mid1 vdd vss BUF
    .ENDS MID

    Xtop O1 I1 vdd vss MID
    VDD vdd 0 DC=2
    VSS vss 0 DC=0
    V1 I1 0 PULSE (0 2 0 1n 1n 70ns 100ns)

    C1 Xtop.Xnext.node1 vss 1e-15

    .TRAN 1n 200n
    .PROBE v(Xtop.*)

    I get the nodes in simvision regardless of whether C1 is present or not. I'm using sub-version  14.1.0.804.isr12


    Regards,

    Andrew.

  • Hi Andrew, thanks, that's the kind of circuit and situation I was describing. The version is: 13.1.1.049 64bit 04/15/2014 04:15 (usimamd64-46). So, it sounds like it should work.

    I tried your netlist and it works for me - I can see node1 in SimVision. So, perhaps the issue specific to my netlist but in principle it's the same as the case you created.

  • Marc,

    I just tried the netlist above with the same version as you, and it seems to work for me. So I suspect there must be some subtlety my simple example is missing. Perhaps you could check my netlist too - I just did:

    ultrasim -raw forumultra.raw forumultra.spi

    (the netlist was in forumultra.spi)

    I used: Version 13.1.1.049  64bit 04/15/2014 04:15 (usimamd64-46)(exactly what you used).

    Regards,

    Andrew.

  • Yes, I tried your example and it worked. Unfortunately I can't share my netlist.

    The probe statements are:

    .probe tran v(Xtop.*) preserve=all depth=2
    .probe tran v(Xtop.Xnext.*)

  • Marc,

    I think the best thing is for  you to work with customer support to investigate what is different about your case that cause this problem.

    Regards,

    Andrew

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