Hi Steve,
I am not sure what you mean when you say that the standard Wein works beautifully and the inverted Wein latches up.
Are you aware that the resistors R5 and R6 much also be swapped for the inverted version?
In other words, if the standard version has R5=10k and R6=5k, then the inverted version requires swapping R5 and R6, so R5=5k and R6=10k. It's only then that we see similar action.
I'll suggest these sufficient conditions. (Keep in mind that sufficient conditions allow that there might be other ways that don't obey these conditions)
1. Barkhausen Criteria must be met for a nonzero amplitude and frequency
2. Stimulus signal at the correct frequency must exist at small amplitude
3. Gain > 1 must exist for small amplitudes at the frequency
4. Gain must saturate as amplitude increases at the frequency
5. No RHP poles exist to cause instability when gain saturates to G<1
I think 5 will avoid the latch up and multivibrator issues.
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Anyway, that's my best attempt.
First, im not sure what you mean by the most recent circuit latching up and the more standard version working fine. Is this in simulation? They both should work fine otherwise we've found a circuit that meets Barkhausen and doesnt oscillate
But maybe you can clear that up. What i cant see is how you got one to work and one not to work, and the one that 'works' somehow works without negative feedback?
So anyway, what i am proposing is that for point number (2) as outlined by Steve, that we drop the 'noise' requirement, and we drop the 'turn on' requirement, because that is more general than what is needed, and as i already said twice now 'noise' does not guarantee start up and neither does turn on. ... Do you see why i stress this point now? [
The "most recent circuit" is the one from Winterstone in post #78. here the negative feedback path requires R5/R6=0.5. When I simulate this, the output latches to one of the power supply rails. It doesn't oscillate. I don't claim this is necessarily the correct answer, but it is what I got. It seemed reasonable to me, but I'm planning to double check the equations and implementation later today.
Here we have a similar situation. The additional elements (capacitor, resistor) enable a stable dc bias point - however, again point (4) of our list remains to be violated (as mentioned above).I also simulated the original topology from Winterstone in post #54. This topology uses a DC blocking cap in the positive feedback path. When I simulate this, I get the multivibrator oscillation. I also don't claim this result is necessarily correct, but it also seemed reasonable to me. I'll double check this one too later today.
Hi again,
I didnt mean to completely cancel condition #2, i meant to replace it with a more definitive requirement.
For an ideal loop of wire we satisfy Barkhausen but it does not oscillate. What makes it oscillate is to induce a current of some frequency that has a wavelength equal to an integer multiple of the length. So it satisfies the first two requirements (gain 1, phase shift 0 at the right frequency) but it cant oscillate because there is no energy of the right frequency. Perhaps this is getting too theoretical here, but that's part of what i am after.
... no definitive provable, repeatable condition can be stated.
So you think there is no reasonable conclusion? Some things that are more complicated take more time to resolve. Perhaps you think this is not the forum for such a discussion?
hi all,
On taking time to look at what the online web documentation regarding the Barkhausen criteria for a circuit to oscillate.
I read that this subject has been often discussed/debated in great detail at many levels and no unequivocal resolution has ever been produced.
IMHO the original question 'Is there a rigorous oscillation criterion?' is ambiguous and no definitive provable, repeatable condition can be stated.
I should also add that I have been reading the posts on this thread and noting the amount of time and patience our members are putting in trying to find a definitive solution and the difficulty entailed, is what prompted me to do some online reading of the subject.
As far I can see no one has considered the temperature effects on the imagined marginal circuit, ie: would a practical circuit oscillate over a range of temperatures.
Eric
You can be sure that I also did some "online reading" before. And not only "online" - I have consulted several textbooks with high reputation.
In case I had found a satisfying answer, I wouldn`t ask for some new thoughts in this forum.
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