Garrett.Neaves wrote on Dec 2^nd, 2011, 6:48am:


Thanks for replying and - yes - of course I agree (more or less).
On the other hand, the degree of simplification is the same for interchanged input nodes leading to the classical circuit configuration, which is widely used.
Thus, the "excessive idealization" alone cannot be used as an argument.
Rather, I think it is the knowledge we have (contrary to the computer resp. the simulation engine) about the conditions for a stable dc operating point.
Are there other (additional) aspects?  

buddypoor wrote on Dec 2^nd, 2011, 7:48am:


I think we are seeing the same thing from slightly different points of view.  From my point of view, when a model becomes idealized to the point that it gives fundamentally contrary behavior then I would say that this is a sufficient condition for describing it as "excessively idealized".  

The configuration of an ideal opamp with resistive divider negative feedback does not give fundamentally contrary behavior and therefore is not necessarily " excessively simplified.  In fact, it is often a very useful model.  

buddypoor wrote on Dec 2^nd, 2011, 9:19am:


I like the kind of thinking represented by this question.

I think that there is no general way to know in advance.  

In specific cases, we can see a warning as soon as we see that the ideal modelling result is contrary to what we think we know about physical circuits.  Then, we can do some investigation by, for example, replacing the ideal models of the most complicated components by ones known to reasonably model physical components. Such as replace, the ideal op amp with a known physically representative model.

In general, we need to always ask if our modelling results are reasonable by testing them against something.

Of course, you already do that.  I am just saying that I think that what you are already doing is the right thing to do as far as I know.  I do not know of any general way to know in advance.

loose-electron wrote on Dec 2^nd, 2011, 11:59am:


But you shouldn't blame the simulator in this case. The same applies to each linear oscillator that is simulated without any "kick-off", that in reality is provided by the switch-on action. The user must know that such an "artificial" help to start is required.

hello buddypoor,
could you please send those moving poles paper titles or papers  and this recent simulation procedure paper to my gmail raja.cedt@gmail.com   ?

Thanks,
Raj.

buddypoor wrote on Dec 2^nd, 2011, 12:24pm:


How about enough gain & phase in a loop to sustain-build an oscillation based upon noise or other non-ideal effects?

"Loose-electron, excuse but (due to my limited knowledge of your language) I don't get the contents of this sentence. Do you mean that there can be other "starting aids" than the the power switch-on? (That's clear to me, of course)"

German? Sorry, I speak some French and Spanish, but not german.

Let me explain with simple language.

1. A tranient simulation does not show the effects of noise or mismatch unless you put a transient noise model into the simulation, or put a set of mismatches into the simulation.

2. Both noise and mismatch are often not included in a transient simulation.

3. Noise and mismatch models can be inserted into a transient simulation if needed.

4. An oscillator, in silicon, not in simulation, starts to oscillate due to sufficient gain and phase parameters in the electronic circuit.

5. The electronic circuit also has noise and/or offsets being amplified in the circuit.

6. A "switch on" is not the only thing that will start a device to oscillate.

7. Sufficient loop gain, will take anything (noise, offsets, injected glitches due to a switch flip) and cause a repetitive amplification of that which builds in amplitude as an oscillation.

Hopefully a bit clearer.