Stabilizing techniques for transistor amplifiers are well known, and as we know the frequency of operation we can make sure of stable operation in that band. However, in oscillators and specifically parallel oscillators which oscillation frequency is wished to be defined by feedback loop length (phase delay) we end up with existing multiple oscillation modes. e.g. equivalent series feedback mode at low frequency.
my question is that in such oscillators how can we make sure of other modes suppression? of course we can check startup condition for modes, how ever this is an analysis technique not synthesis.
my intuition is that as oscillation starts from DC we should keep amplifier stable all the way to oscillation frequency. but I am not sure.
I appreciate it if you share your experience with others.
thanks a lot
From the control view, you have to keep your poles on the left side of the imaginary axis. This means that the amplifier has to be insulated from the oscillator or work at different frequencies. Also usually it is said that in a high-frequency world, the amplifiers oscillate while the oscillator does not!
As a result, I think your question can be answered if you let us more details such as circuit structure, desirable oscillation frequency, type of amplifier, oscillator, and feedback.
Some issues arise in e.g. third harmonic quartz crystal oscillators. What can be done as example is first creating LC oscillator tuned for designed frequency while the essential loop is going via element having electrical characteristics identical to quartz crystal at the desired third harmonic (might be simply electrical short). Then, the quartz crystal replaces that element.
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