jasmin_123 said:Hi, zorro,
Why not necessarily the output has to grow? If signal at some frequency is increasing while traveling over the loop and remains in phase (G>1 at zero phase implies just this), then the output does necessarily have to grow.
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The output always have to grow for a G>1, P(G)=0. Why for the same G>1, P(G)=0 it does grow in some cases and does not grow in the other cases? Why?
Jasmine
jasmin_123 said:The loop gain, G(s), is a network function defined for ZSR only. The oscillator response is a ZIR one. Does the G(s), defined in ZSR only, have meaning in ZIR? It seems that not.
Consider, for example, a zero-order amplifier with the gain A=10 and a feedback network with the feedback transmission B(jwo)=0.2. When you measure G in Fig. 1, you get G(jwo)=A*B(jwo)=2. But in ZIR (see Fig. 2), B(jwo)=2 has no meaning, because if A=10, then B(jwo) should be 0.1! and G(jw0) should be 1!
Conclusion: A, B, and G has no meaning in ZIR, and, hence, a single value of G says nothing about the oscillator stability.
jasmin_123 said:"Oscillator is like an amplifier with gain at only one frequency."
This is wrong. Oscillator with zero noise is not an amplifier. It does not have any input.
jasmin_123 said:"I am aware about https://web.mit.edu/klund/www/weblatex/node4.html
Unfortunately, these pages give no intuitive explanation to the question I asked.
jasmin_123 said:"A different site led me to the write answer:
https://www.ee.bgu.ac.il/~paperno/Positive_Feedback_Oscillators.pdf
https://www.ee.bgu.ac.il/~paperno/1._Positive_Feedback_Oscillators_Illustrations.pdf
teteamigo said:jasmin_123 said:"I am aware about https://web.mit.edu/klund/www/weblatex/node4.html
Unfortunately, these pages give no intuitive explanation to the question I asked.
Look in depth...
teteamigo said:We should be exigent with theory. Right.
But we can't be exigent with the physical systems. We accomodate to Nature.
jasmin_123 said:Note that an oscillator does not need any noise to oscillate.
jasmin_123 said:To understand a practical oscillator you first have to understand it without noise and then to add noise. With no noise its poles are to the right of the jω axis, and this is an oscillator. With noise, its poles are to the left of the jω axis, and this is an amplifier that amplifies the noise at all the frequencies but does it selectively, depending on the phase response of its feedback network.
jasmin_123 said:I repeat this once again: "oscillator does not need any noise to oscillate."
Its oscillations in steady state can originate from its natural response.
(If you do not believe, you can simulate a noise-free oscillator in SPICE.)
jasmin_123 said:With noise, the oscillator poles shift to the left, its natural response decays,
and its forced response defines the steady state.
jasmin_123 said:This is elementary... Take care!
jasmin_123 said:"Oscillator: amplifier+feedback network." Not always.
Oscillator is simply an unstable circuit, with unstable poles. No input.
Amplifier is a stable circuit stable, with stable poles. Noise is the input.
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