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100 KHz Crystal Oscillator
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rcbuck:
I've been experimenting with a 100 KHz crystal oscillator with some success. I know these are really not crystals but are tuning fork oscillators at these frequencies.

I am using a Mouser part number 815-ABS25-100KT part. I can get the part to oscillate by adjusting the trim cap after powering the circuit up. I can bring it on frequency to exactly 100.000 KHz. However, if I power the circuit down and back up, the oscillator will not start without adjusting the trimmer until it starts. I can then adjust it back on frequency.

Circuit I am using is attached. Is there a better circuit that I can use?
floobydust:
Some relevant threads:
https://www.eevblog.com/forum/projects/low-jitter-100khz-oscillator-for-ad/
https://www.eevblog.com/forum/projects/level-translate-the-output-of-a-tcxo-crystal-oscillator-module/
Benta:
Increase R33 to 500k...1M.
The driving power for tuning fork crystals shouldn't be higher than around 1 uW. You're overdriving it.
rcbuck:
floobydust, thanks for the links. Jitter is not important in my application. But the oscillator has to start reliably on power up. It looks like the 74LVC1GX04 that you referred to in the second link is probably the best approach.

Benta, I will try your idea and see if it works. However, according to several data sheets for different crystals, 47K would be the best value to be used for R33. That sets the high frequency cutoff at 125 kHz if C24 is set to 24 pF. Getting low frequency crystals to work is always a challenge. I have had problems with the 32.768 kHz ones in the past.
Benta:
Main mistake: don't use Schmitt triggers for oscillators. Big no-no. Best solution is an unbuffered inverter:
74LVC1GU04 is ideal.
The output buffer you can leave as 74LVC1G14




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