Carl F
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Posts: 4
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Hi,
After some search on forums and other sites, I have come to a conclusion that the oscillator circuit shown in the attached schematic could be a good implementation for robustness against temperature drifts and manufacturing spreads. My goal is that the oscillator circuit should bring out the series-resonance properties of the resonator as clearly as possible, and suppress influence from the rest of the oscillator circuit as much as possible. I hope there is no obstacles such as patents, etc, prohibiting free use of this circuit. If so, I would be highly greatful getting informed.
I have divided the drifts/spreads into two groups, coming from the two circuit parts: the circuit *around* the resonator, and the resonator itself. The resonator can be of any series-resonant type, such as a series LC circuit, a ceramic resonator, or a crystal, etc.
To make the resonator work as cleanly as possible based on its series-resonance properties only, and as little as possible based on its parallel parasitics (incl circuit parallel parasitics), I have looked for oscillator circuits that work at (or very close to) zero-phase operation between the ac voltage and current in the resonator. The circuit driving the resonator can simply be a fast in-phase transimpedance amplifier, giving up to a couple of degrees of phase lag, where the resonator ac current is the amplifier input current. This amplifier must not give a phase lag e.g. in the order of 90 degrees, which then is phase compensated back to about zero degrees before its output voltage is fed back to the resonator, because (non-matched) drifts of e.g. 10% of 90 degrees, giving in the order of 10 degrees resonator i-v phase error, could cause a significant oscillation-frequency shift, whereas, 10% of 1 degree is likely to give negligible frequency shift. Furthermore, I believe that this oscillator circuit has the potential to utilize the inherent resonator Q value very well, since the only terminal that the resonator is connected to is a low-impedance emitter, which will degrade the total circuit Q value negligibly.
So, if you have any kind of comments on this circuit or oscillator reasoning in general, or happen to know even better solutions to the task of designing high precision/stable oscillators, and can consider to share them, I'd be highly greatful!
Regards, Carl F
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