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Aug 22nd, 2019, 7:45am
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Floating node using spectre option (Read 934 times)
Gp
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Floating node using spectre option
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.
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Geoffrey_Coram
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Re: Floating node using spectre option
Reply #1 - 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.
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Horror Vacui
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Re: Floating node using spectre option
Reply #2 - 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.
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Ken Kundert
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Re: Floating node using spectre option
Reply #3 - 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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