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multiple gnd's passive components only system problem

robert 21

Hello , i have a system with multiple device represented by R L C components each device has its own ground, i wanted to make POLE ZERO simulation on it.

at first for the simplisity i made  all the devices stacked and one big cirtuit(which was verified in a much simpler simulator called LTSPICE)

After that i tried to convert each device as a symbol as shown bellow.
when In cadence virtuoso i didnt use symbol to simplify the schematics it gave me errors like,

1.no DC path from node "net.. to ground" Gmin installed to provide a path

2.Fatal: the following braches form a loop of rigid barnches(shorts) when added to the circuit

3.why i tried to make subsimbols it gave me an error in bettween the connection of the devices saying they are floating although they are not(and i ran it fine in LTSPICE)

i really want to use the potential of cadence virtuoso to analyze to the fullest extent this passive component network

Where did i go wrong?

Thanks

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  • Dear robert21,

    robert 21 said:
    1.no DC path from node "net.. to ground" Gmin installed to provide a path

    Perhaps I am overlooking something in your circuit, but if I zoom in as much as I can to enhance my view of your screenshots, the error reported is justified as your circuits do not have a DC connection to ground. I've annotated two of your screenshots to illustrate that you have not provided a DC path to ground and attached the two files. Therefore, to enhance DC convergence, spectre indicates it is adding a small conductance to provide a DC path to ground. LTSPICE I believe is based on SPICE. It does not warn you, but likely also adds a small conductance to achieve DC convergence. If you study the LTSPICE simulator parameters, you will likely find an analogous parameter to Gmin. HSPICE, for example, includes a gmin whose value is a factor of 10 greater than the default for spectre (1e-11 in lieu of 1e-12 mhos).

    With respect to the fatal error, I do not know the value of your resistors. However, if they are too small and you are simulating with spectre APS, they may be shorted out. One possible way to avoid this is to set the "preserve_inst" option to all. You can do this in ADE using the high performance simulation GUI shown in the attached figure.

    Also, please verify that none of your subcircuits have multiple DC sources driving same node to different DC voltages in all of your subcircuits. This will also cause this fatal error.

    Shawn

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