From: Soeren D. S. <soe...@gm...> - 2013-07-21 13:21:24
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Am 21.07.2013 14:26, schrieb roucaries bastien: >> But of course "gmin" and "short" are modifications to the circuit. I >> think it would be possible to reduce the need for them by a better >> implementation of the algorithm. > > Gmin and gshort replace a lot of time the missing step not given by > the electrical engineer. In the case of biasing a tunnel diode, it > make sense from a phycical point of view: your source are not > perfectly constant but a heaviside step. Make sure not to confuse gnucap's "gmin" with Spice's "gmin". The former is similar to Spice's "rshunt". Is it always harmless to add a resistance of 1e12 Ohm to ground in each node? In most cases, it probably is, but users of circuit simulation programs should be educated about it, so there won't be any surprises. Adding a series resistance to a voltage source seems both more effective and more harmless to me -- really, who is going to notice 10u Ohm? It's perhaps a good idea to either add this as a global option or incorporate it as a parameter in the ideal voltage source model. Currently, Qucs adds a virtual resistance on demand inside an integration step. I'm not sure if that's a good idea because it modifies the circuit while the simulation is already running, so the result from the previous integration step may be inconsistent. It's important for users to understand that leaving out certain parasitic components sometimes doesn't simplify things but actually makes them trickier. Sören |