Touch a crystal to make it start-up to ocsillate.

[ken_cn]

Dear all,

I encountered a very strange problem.
I used a crystal for a on-chip DCXO, but sometimes the oscillator did not start up after power-on.
At this time, I need to use my fingers to touch the crystal output cap. on the PCB to make the DCXO start to ocsillate.
I totally have no ideal about it.
Could you give me some help on this problem?
Thanks in advance!

Best,
Ken

 

[BradtheRad]

Apparently the oscillator needs a bit of instigation to get going. A fraction of a volt from your touch could be enough to do the trick.

We all carry a bit of static voltage. Maybe a lot. Maybe less than a volt. It changes continually.

Try this with your meter. (If you have an oscilloscope it's even more dramatic.) Set the scale to the most sensitive reading. Then touch the probe lead, and move around in various ways. Rub your feet on carpet, rub your hands on plastic, try any number of things, etc.

You'll find there's at least a few actions that will cause your volt reading to jump up and down.

 

[RCinFLA]

You don't have enough loop gain to initially amplify the device noise to build up oscillation.

You did not post the frequency or circuit so specific suggestion is not possible but you may solve the problem by changing the loading capacitors ratio while keeping the net capacitance loading of crystal the same.