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Simulating stability of single ended circuit wrt to a local gnd, not gnd!

Bill Toole

I am trying to simulate the stability of an LDO with respect to a local ground on chip. I use a 0V voltage source to break the feedback loop and get fairly normal looking results when I include bondwire inductance on the vcc input line only and local decoupling caps (purple lines in attached plot). When I include bond wire inductance (~ 2nH) on the gnd line though I get very strange results, mainly very significant gain and phase peaking at high frequencies (> 1GHz).  It appears that stb analysis runs with respect to the global gnd! Is there a way to use a probe to run stb wrt to the local gnd? Is it possible to use diffstbprobe for this purpose?  The help file mentions a "localgnd" parameter but I cannot figure out how to add the parameter.

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  • Andrew Beckett

    On the stb choose analysis form, click the Options button, and then at the bottom in the additionalParams field, enter localgnd=I1.I2.gndName (where I1.I2.gndName is the hierarchical path down to the node you want to be the local ground - use dots as hierarchy separators).

    Regards,

    Andrew.

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  • Andrew Beckett

    On the stb choose analysis form, click the Options button, and then at the bottom in the additionalParams field, enter localgnd=I1.I2.gndName (where I1.I2.gndName is the hierarchical path down to the node you want to be the local ground - use dots as hierarchy separators).

    Regards,

    Andrew.

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