On Sat, Feb 22, 2025 at 11:55 AM, Carlo wrote:
Do you think .options gmin=<value> is actually the same as "Add GMIN across current sources" checkbox?
No, they are not the same.
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".options gmin=<value>" sets GMIN to a number.? GMIN is used in a number of places in SPICE/LTspice, including in parallel with EVERY semiconductor junction.? GMIN is used in other places too.? If you search LTspice's Help for "GMIN", you can see some of the other places.
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Checking the checkbox to "Add GMIN across current sources" adds yet another place where a conductance with value GMIN may be added.? But for that to work, first GMIN needs to have a value.? Giving GMIN a value does not cause it to magically appear in extra places where it does not normally appear.? Note that GMIN must always have a value.? SPICE won't run without it.
In other words, does .options gmin=<value> add a <value> Siemens conductance in parallel to each (controlled or independent) current sources as well ?
No, not unless you check that checkbox!
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Again, I note that GMIN always has a value.? Its normal value is 1e-12, as shown on the Help page for .OPTIONS.? It can also be set in the Control Panel, and that is the same GMIN.? It might not be possible to set GMIN to 0.0000000000000.? Trying to do that might instead set it to its default value of 1e-12.? SPICE/LTspice might not run at all if GMIN were actually set to 0, or if it did, it might run poorly.? All this has nothing to do with current sources.? GMIN is a necessary convergence aide to help SPICE converge when there are semiconductor PN junctions, as well as a handful of other things.
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(Interesting note:? LTspice also uses the value of GMIN to set a minimum resistance value, in certain cases where a resistance must not reach zero.? That is kind of contrary to engineering logic, because GMIN is supposed to be a small conductance, not a small resistance.? But it silently does that anyway.? I guess it does this as a way of avoiding yet one more OPTION variable.? Yes it's cheating, but it works.)
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Andy
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