From: Stefan Jahn <stefan@gr...>  20050930 11:48:48

On Fr, 30.09.2005, 11:19, Eric Tanguy wrote: Hi! >> >> >>> Ok. In fact it depends what you want to see. I need to see the >> >> >>> permanent >> >> >>> regime to estimate the signal deformation so i need to analyse >> the >> >> >>> signal >> >> >>> in more time and thus the simulation is quiete longer. But it >> seems >> >> >>> also >> >> >>> interesting to see "the real transient regime" with loading of >> >> >>> capacitors. >> >> >>> Maybe it could be an option in transient analysis ? >> >> >> >> >> >> I just had a short glimpse on the 'ampli.sch' file. When you set >> >> input >> >> >> capacitor to 0.033u and output to 0.5u (divide both by 100) then >> you >> >> get >> >> >> the "permanent regime" after the first swing... >> >> >> >> >> >> >> >> > Yes you're right but it does not reflect the reality it's just an >> >> artefact >> >> > for simulation so it's difficult to explain that to young student >> >> whereas >> >> > the problem does not exist in orcad because it makes simulation >> around >> >> a >> >> > bias point by default. >> >> > It could be very helpfull to have (like in orcad) the possibility >> to >> >> > choose. >> >> >> >> Hm. I am not sure about your statement about "reality"  "simulation >> >> artefact". I rather assume that if you switch a sinus source on, you >> >> really get the results reflected by the simulation and *not* a >> squeaky >> >> clean sinus at the output. I'm going to investigate this anyway... >> >> >> >> Michael: Any comments on this? >> >> >> > The reality is : the values of the real capacitors that i will take to >> > realize the circuit. Decreasing the value to reduce the transient time >> > is just for the simulation and it's not so simple to explain this to >> > student. If you put a sinus source on the real circuit and use an >> > oscilloscope to visualize the signals you will never see the transient >> > part of the signal except if you add rectangular modulation. That's >> why >> > in orcad the default transient simulation is around the bias point. In >> > orcad you can also simulate the "complete" transient analysis but it's >> > not done by default. This is just because this is default way in orcad >> > but may be the goal of qucs is quiete different. It's not very >> important >> > it's just to have a free altenative to orcad and so on with mainly the >> > same possibilities and more i hope. >> >> You may shift the "Start" time to a later point (when the "steady state >> regime" is reached) in the transient analysis properties in Qucs. Is >> this an option probably? >> > > Hello, Stephan, you are right it is an option and it works fine. Thanks. > I don't why i didn't think to this before! I have 2 more quesitons : > how it is possible to make a parametric simulation about temperature ? > how to obtain the FFT of a transient result to estimate distorsion ? > One more time thanks for the help. For a parameter sweep you need to place a "Parameter Sweep" component onto the schematic. Apply any variable (e.g. T or Temp or TEMP whatever) to be swept in the parameter sweep properties. Then apply the (same) variable to the "Temp" properties of components you want to sweep. Please note: Temperature models of diodes/transistors are not yet implemented completely. Unfortunately the FFT of time signals is not yet implemented, but it's on the TODO list. It just went two/three items up :) Cheers, Stefan. 