Huge BLE carrier frequency drift

[bluera1n]

Hi,

I have huge BLE carrier frequency drift, which cannot pass FCC requirement.

The drift is 256kHz which seems not normal.

I'm using 32MHz 10ppm xtal so drift should be few tens of kHz AFAIK.

I got images from the test lab as below.

Any comment will be appreciated.

Thanks.

[ketiljo]

It looks like you're having an offset, not drift, that's different. 

The crystal is probably not loaded correctly. Check the datasheet for the CL value of the crystal and calculate the correct value of the load caps as: 

Ccap = 2 * CL - 4 pF.

For example, a crystal with CL = 12 pF will require 20 pF caps. Round down to 18 pF.

[bluera1n]

Ok. Now I knew it's offset not drift. Thanks.

BTW, CL value of the xtal I'm using is 8pF.

So I'm using 12pF according to the calculation you mentioned.

I think xtal itself has a problem.

Do you think so?