Jenny Lee wrote: > 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. I fit the impedance into a six-element > equivalent model (similar to 4-element equivalent model of Quartz) and placed > in a Colpitts configuration for the simulation. In the open-loop gain/phase > plot, the peak barely passes 0 dB no matter what C1 and C2 I chose. For > transient simulation, it does oscillates, but on a PCB, the circuit won't > oscillate! I'm including the device impedance, circuit schematics and > simulation results as an attachment. I've managed to oscillate 20 MHz device > which has a higher maximum impedance than 34 MHz devices both in simulation > and on a PCB - but for this I followed the guidelines of Colpitts for Quartz > ranging at 10~20MHz. But above 20 MHz, for Quartz, overtones seem to be the > way to go due to the manufacturing so I couldn't find any reference or > circuits that operates Quartz for 30 MHz~50MHz ranges at a fundamental mode. > I can only use fundamental mode for my device... I would really appreciate > if you could share some of your experiences with Colpitts or any suggestions > of what I can try to make it work... Thank you!-Jenny > Jenny
The so called overtone oscillators can also be made to oscillate at the fundamental by suitably selecting the mode selection components. The Driscoll oscillators with a relatively low Q tuned collector tank are perhaps easiest to design. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
