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Simulators >> AMS Simulators >> Floating node using spectre option
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Message started by Gp on Jul 30th, 2018, 5:31am

Title: Floating node using spectre option
Post by Gp on Jul 30th, 2018, 5:31am

Hello All,

How can I found floating node in design using spectre option?

Another question is, any difference between the floating and dangling node?


Thanks.

Title: Re: Floating node using spectre option
Post by Geoffrey_Coram on Aug 1st, 2018, 7:14am

A dangling node usually means there's only one connection (but it's a resistive path). If you had

r1 dangle 0 50

then "dangle" is dangling, but not floating.

If you had

c1 dangle 0 1p

or if you have

c1 float 0 1p
c2 float 0 2p

then these nodes are both floating -- no dc path to ground. But "float" has two connections, so it's not considered dangling.

Title: Re: Floating node using spectre option
Post by Horror Vacui on Jul 24th, 2019, 5:32am

Is there any spectre option which could REPORT any potential floating and/or dangle instances? It could be a useful way to narrow down the cause of convergence issues.

Title: Re: Floating node using spectre option
Post by Ken Kundert on Jul 24th, 2019, 11:46am

The topology checker naturally finds, reports, and fixes nodes without a DC path to ground, which includes floating nodes. Dangling nodes do not cause convergence issues as long as they have a DC path to ground.

Dynamic floating nodes (generally caused by Verilog-A models) are not reported with a dedicated message. Instead, the simulation fails with a 'Singular Jacobian'. When it does, it generally reports the nodes or branches where the problem was found. This often leads you to the problematic node or branch.

-Ken

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