hello everyone. I am trying to use qucs (which in my mind seems to be the
best of gui- driven, no hassle eda foss software) for a report i have. I
hope you put up with my newbie questions
a) Transient simulations. Dunno why i just cant make them work... even a
simple one like http://users.ntua.gr/el04092/bah.sch
b) I am also trying to make a dc analysis of the 741 opamp, but qucs doesn't
like my voltage sweeping http://users.ntua.gr/el04092/1_2_apomonwths_dc.sch
more to come :)
any help highly appreciated
From: Stefan Jahn <stefan@gr...> - 2007-05-01 08:32:09
Am Mo, 30.04.2007, 13:14, schrieb Alexandros K-K:
> hello everyone.
> I am trying to use qucs (which in my mind seems to be the
> best of gui- driven, no hassle eda foss software) for a report i have. I
> hope you put up with my newbie questions
> a) Transient simulations. Dunno why i just cant make them work... even a
> simple one like http://users.ntua.gr/el04092/bah.sch
the frequency of the source is 1GHz. with tstop=1ms you try to simulate
a lot of periods..., so set frequency to e.g. 2kHz.
> b) I am also trying to make a dc analysis of the 741 opamp, but qucs
> like my voltage sweeping
put a small resistor in the feedback-path to make it work...
hope this helps,
From: Stefan Jahn <stefan@gr...> - 2007-05-12 17:32:26
Am Sa, 12.05.2007, 17:02, schrieb Alexandros K-K:
> the transient simulation works like a charm! thanks a bunch
> however the 741 thingy doesnt work, putting resistors doesnt change a
> replacing the uA741 with a "generic lossless" opamp from nonlinear
> components works, but it's not exactly what i need i guess
> the error message is like
> WARNING: DC1: DC analysis failed, using fallback #1 (source stepping)
> WARNING: DC1: DC analysis failed, using fallback #2 (gMin stepping)
> repeated a few times
> maybe uA741 model is wrong in some way?
Ok, I tried your simulation. The messages are warnings. So you can rely
on the results. Also they look good, even without a resistor in the
You use the "generic lossless" opamp if you want to. It depends on what
you want to achieve or learn...
From: Stefan Jahn <stefan@gr...> - 2007-05-12 21:24:52
Am Sa, 12.05.2007, 22:03, schrieb Alexandros K-K:
> you are indeed right, they are mere warnings. a friend of mine (a new
> convert) complained about not being able to sweep the dc voltage due to
> warnings, however it works for me
> a new question: http://users.ntua.gr/el04092/example1.sch
> I want to insert a 5V dc bias to the signal. At least on the breadboard,
> do that by connecting a 10V dc source to 2 resistors of the same
> and drawing the ac signal through them. However as shown on the example, i
> think the ac signal nulls the dc bias (i hit F8 for a quick view)...
Nothing's wrong. Please remember that an AC voltage source is a short
for DC. So you need either a dc-block or a normal capacitor between the
pos. terminal of the ac-source and the vout node.
Hope this helps,