buddypoor
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Hi Rajasekhat, thanks again for replying. I am really happy that you are willing to discuss with me some oscillator properties. Regarding the well-known double-integrator-oscillator (DIO), I have mentioned already some key points in my former posting (last sentence in brackets). This oscillator is a very outstanding one since it is the only circuit I know, which fulfills the phase condition over a broad range of frequency (if, and only if the opamp is considered to be ideal!). More than that, any additional gain within the loop changes the frequency of oscillation without touching the oscillation condition. This also is in contrast to all other harmonic oscillator circuits. Here are some details: 1.) For real opamps the phase will cross the 360 deg line (oscillation condition) at one frequency f1 only. The loop gain at this frequency is above unity. 2.) Question: For these conditions, every other oscillator - except the DIO - will oscillate at f1 with rising amplitudes until (severe) clipping occurs. But the DIO oscillates at another frequency f2 for which the loop gain is unity. This oscillating frequency f2 is (very often far) above f1. 3.) More than that, the phase of the loop gain at f2 is beyond 360 deg. (In some cases: -5...-15 deg. !!!). 4.) The oscillator amplitude reaches its maximum value (somewhat below the supply rail) with minor clipping only. In some cases practically no clipping can be observed. 5.) For the first time period (before the maximum amplitude is reached) the frequency is somewhat below f2. 6.) From the above, I would conclude that an oscillator with two IDEAL integrators (which do not exist, fortunately) cannot oscillate at all (?). _______________ These are some properties which I call "surprising". What do you think? Or somebody else in the forum?
Regards
Added somewhat later: To summarize in short: All harmonic/linear oscillators - except the DIO - oscillate at a frequency which can be derived from the loop gain (phase=zero, gain>0 dB due to safe start-up). In contrast, the DIO oscillates at a frequency for which the loop gain is 0 dB and the phase is some degrees below zero. However, the DIO never has any start-up problems.
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