stefannm
Member level 1
I have designed and had built a 4.9MHz pierce oscillator on an IC. I have it in the lab and everything looked okay for a while. The oscillator seems to start up and have decent frequency accuracy. I have noticed when I put my finger on the crystal pins, the oscillator dies until I remove my finger, then it started right back up.
I have tried a variety of load cap sizes (26pF to 39pF). It seems to start up with expected shifts in frequency, but always has the susceptability to the finger test.
I am on a 3.3V supply and the amplitude of the oscillation is ~2V which implies sufficient -R. Is this correct?
How concerning is this? Right now I am really concerned. Any ideas how to fix this? Is it a case of insufficient loop gain?
Is it possible to have too big of a feedback resistor? I have 10M+ for other reasons.
BTW it is a CMOS oscillator in an Eric Vittoz type architecture.
Thanks in advance for any help,
stefannm
I have tried a variety of load cap sizes (26pF to 39pF). It seems to start up with expected shifts in frequency, but always has the susceptability to the finger test.
I am on a 3.3V supply and the amplitude of the oscillation is ~2V which implies sufficient -R. Is this correct?
How concerning is this? Right now I am really concerned. Any ideas how to fix this? Is it a case of insufficient loop gain?
Is it possible to have too big of a feedback resistor? I have 10M+ for other reasons.
BTW it is a CMOS oscillator in an Eric Vittoz type architecture.
Thanks in advance for any help,
stefannm