## Re: [Qucs-help] Surprising simulation results from Qucs...

 Re: [Qucs-help] Surprising simulation results from Qucs... From: Stefan Jahn - 2006-06-02 07:33:18 ```Am Mi, 31.05.2006, 19:39, schrieb Rob Frohne: Hello Rob, >>> The discrepancy is that the DC analysis gives Vout as 5.98 volts and >>> the >>> transient analysis gives it as 12 volts. Sorry I wasn't as clear as I >>> should have been. I did download and compile 0.0.9 and it gives the >>> same result. >>> >> >> Yes. I noted this as well. But as I said: Try setting the AC- >> Voltage source amplitude to 1V and *see* where the descrepancy may >> come from. >> >> >>> I noted you are looking for an algorythm for transient analysis of >>> transmission lines on the web page. Is this still so? If so, I may >>> give some thought to it. >>> >> >> You can have a look at the technical description >> ; >> 6.5 Components defined in the frequency domain >> Page 103-109 >> >> There I already documented a lot regarding this issue. Probably you >> can review this and tell about your thought then? >> > > I will have a closer look at that document. It looks good. If I have > comments I'll let you know then. > > I still think that the DC analysis should give the same as the Transient > analysis in the limit as the input AC signal goes to zero. I haven't > done a quick hand analysis on that circuit to find what it says. I > would, but the circuit is at home, and I haven't compiled qucs on this > machine yet, so I don't remember the resistor values. I agree to a limited extend. Imagine a circuit with very large time constants. The DC solution is the average transient solution with unlimited time passed. You can't simulate until infinity, thus the result can differ even without a real contradiction. In your case it is about the two capacitors at the input and output of the circuit. With smaller values of these you're getting probably what you would expect in first place. Does this help? Stefan. ```

 Re: [Qucs-help] Surprising simulation results from Qucs... From: Stefan Jahn - 2006-06-02 07:33:18 ```Am Mi, 31.05.2006, 19:39, schrieb Rob Frohne: Hello Rob, >>> The discrepancy is that the DC analysis gives Vout as 5.98 volts and >>> the >>> transient analysis gives it as 12 volts. Sorry I wasn't as clear as I >>> should have been. I did download and compile 0.0.9 and it gives the >>> same result. >>> >> >> Yes. I noted this as well. But as I said: Try setting the AC- >> Voltage source amplitude to 1V and *see* where the descrepancy may >> come from. >> >> >>> I noted you are looking for an algorythm for transient analysis of >>> transmission lines on the web page. Is this still so? If so, I may >>> give some thought to it. >>> >> >> You can have a look at the technical description >> ; >> 6.5 Components defined in the frequency domain >> Page 103-109 >> >> There I already documented a lot regarding this issue. Probably you >> can review this and tell about your thought then? >> > > I will have a closer look at that document. It looks good. If I have > comments I'll let you know then. > > I still think that the DC analysis should give the same as the Transient > analysis in the limit as the input AC signal goes to zero. I haven't > done a quick hand analysis on that circuit to find what it says. I > would, but the circuit is at home, and I haven't compiled qucs on this > machine yet, so I don't remember the resistor values. I agree to a limited extend. Imagine a circuit with very large time constants. The DC solution is the average transient solution with unlimited time passed. You can't simulate until infinity, thus the result can differ even without a real contradiction. In your case it is about the two capacitors at the input and output of the circuit. With smaller values of these you're getting probably what you would expect in first place. Does this help? Stefan. ```
 Re: [Qucs-help] Surprising simulation results from Qucs... From: Stefan Jahn - 2006-06-06 14:39:55 ```Am Fr, 2.06.2006, 17:08, schrieb Rob Frohne: > Hi Stefan, Dear Rob Frone, > I can't remember the exact circuit I sent you, but if it is the one I > was just playing with, (attached here as common_emitter 1.sch) its DC > analysis gives me around 5.9 volts at the collector, and my hand > calculations give me a saturated transistor with the DC analysis. I do > the same circuit without the capacitors (also attached as > common_emitter2.sch), and I get fine results, so you are right that it > has to do with the capacitors. It seems that the DC analysis should be > the same with or without the capacitors, as for DC they are open circuits. > > It may have to do with something I did while entering the circuit in the > GUI too because I just added the capacitors to the circuit that was > working (no voltage source yet) and it still works. I'll enclose it too > (common_emitter4). Ok. And now you can add again your 1MHz/0.1V input voltage source to common_emitter4 and set the numer of points to 10001 in the transient simulation box and you will see the result which you might have expected in the first place... Cheers, Stefan. ```