From: Stefan J. <st...@gr...> - 2007-02-09 08:24:49
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Am Do, 1.02.2007, 00:44, schrieb Oswald Buddenhagen: hello oswald, >> >> probably you can send me a link (inet) where the circuit is described >> as >> >> well as the actual model your version is based on? >> >> >> > i think i got it here: >> > http://homepages.internet.lu/absolute3/tronic/szdiscr.htm >> >> Ok, thanks. >> Unfortunately there are (partly) no values given for the C's and R's. >> :-( >> > who's the electronics engineer here? ;) hm. you are? > i did some more experimenting ... > with R2 (in my schematic) equal to 6k8 and C1 680pF the circuit actually > works - at 50kHz, which also seems to be really close to the limit. if > R2 is too big, the discharge never triggers, if it is too small, it > never unlocks. if the capacitor is too small, the discharge doesn't > trigger as well. i think especially oscillators are sensitive to their components values. so this is something you can actually expect? > i think i assumed too much ideality from the standard components (i > tried the default transistors before the BC5*) - probably because it is > highly inconsistent (compare the opamp model). the default transistors/diodes are quite ideal in fact. no series resistance, no junction capacitances and alike. that's what the properties are for. > some actual bugs in the gui now: > - the schematic view has some selective repainting problems. it seems to > misinterpret the region information (maybe a global vs. local > coordinates thing) - you can observe it very well by moving a small > window over it. that's probably a Qt "proplem"? > - the widgets in the component properties dialog have weird repainting > problems which temporarily disappear when one first resizes the > dialog, then closes and then opens it again. > this sounds a lot like this thing should go through valgrind. that is as well a Qt problem which is known to us. probably also a general X windows problem? i don't know. if you find out it would be a good contribution to Qt/X i think. > another thing ... not a bug, rather an inherent problem (i assume): the > simulation behavior (primarily time) varies *extremely* between even > almost trivial circuits. for somebody not really understanding *all* the > parameters it is virtually impossible to tune the simulation for > acceptable results; in a more complex circuit it is probably actually > impossible to find a compromise between the local optima. > there should be more/more obvious knobs to limit the cpu time spent on a > single simulation step. ideally, it would also give an estimation of the > quality reached. taking this further, the system could tune itself, at > best for particular subcircuits. who wants to make a PhD soon? ;} you're right this is an inherent problem. i assume you refer to transient simulation. this type of simulation solves a set of non-linear equations. this system has the following properties/problems: * there is an unlimited set of solutions * numerical noise plays sometimes an important role * numerical overflow must also be avoided * a "wide-range time-constant circuit" causes ill-conditioned solution matrix -> difficult to solve * etc, etc., etc. i was constantly working on these issues and tried my best so far to handle all these problems. it's always like part of the problem are in the device models and part of them in the simulation algorithm. i think we already get some good results with the current implementations. new ideas and inputs are always welcome. i suggest you to probably read the technical documentation (qucs-doc cvs) or the pdf file on the homepage. most aspects of transient simulation are covered somehow. remarks on it would be nice and could help me to re-consider some things. also a tutorial about the transient simulation and its properties would be welcome. you could use some example schematics with apparent convergence difficulties and show how those "knobs" and "workarounds" can be be applied to solve these issues appropriately. in fact to triggered a topic which is still worth research, though a thousand times already applied. please don't mind this kind of answer. :-) cheers, stefan. |