[time-nuts] Xtal-like Colpitts Oscillator
hyunjoo_lee at hotmail.com
Tue Apr 1 01:28:51 EDT 2008
Thanks so much for the feedbacks!
-Jenny > Date: Tue, 1 Apr 2008 13:18:18 +1300> From: bruce.griffiths at xtra.co.nz> To: time-nuts at febo.com> Subject: Re: [time-nuts] Xtal-like Colpitts Oscillator> > Max Robinson wrote:> > Jenny asked.> >> > Hi Everyone, I was hoping to get some words of wisdom on my oscillator that > > only oscillates in simulation! I have a MEMS device that resonates around > > 34 MHz at a given bias with Q of 100.> >> > You have already received some very good advice. You might also try a > > transistor with a higher ft. My personal experience is that it's easier to > > get an FET to oscillate in a colpits configuration. You won't be able to > > drive a 50 ohm load from an FET. A buffer of some kind will definitely be > > needed.> >> > Regards.> >> > Max. K 4 O D S.> >> > > Max> > Lowest noise is achieved when the oscillator transistor only conducts > for part of the cycle.> Altering the ratio of C1 to C2 adjusts the duty cycle.> > With the given values of C1 and C2 a high(~ 30ms) transconductance FET > is required given the relatively high resonator ESR (~200 ohms).> Even when using something like a J310 the values of C1 and C2 will need > to be reduced.> > One option achieving a clean low noise output signal is to extract the > output signal via the resonator.> Instead of grounding one end of the resonator it is connected to the > emitter of a common base stage.> > One could even use the Pound technique to interrogate the MEMs resonance.> In which case, determining the MEMs fundamental resonance frequency to > within a few ppm of fr/Q should be possible.> > Bruce> > _______________________________________________> time-nuts mailing list -- time-nuts at febo.com> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts> and follow the instructions there.
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