How measure XTAL with frequencemeter tuning the right frequency ?

[Michael_C]

Hello,

To finaly adjust the inside crystal capacitor at the end of production, I need measure the LFXO and HFXO frequencies signals to fine tuning. How should I do ?

Best regards.

Michaël C.

[Bendik Heiskel]

Hi Michaël,

The easiest way to measure the LFXO without adding additional load to the crystal is to configure the GRTC to output the LFCLK clock to a GPIO pin:

https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/grtc.html#ariaid-title5

The HFXO is a little trickier to tune, the simplest way is to use the radio frequency accuracy, as the carrier frequency accuracy is directly dependent on the 32MHz crystal accuracy. To do this radio should be configured to output a unmodulated carrier. The radio test sample can be used to do this:
https://docs.nordicsemi.com/bundle/ncs-latest/page/nrf/samples/peripheral/radio_test/README.html#user_interface

 

This tuning does not need to be done for all devices in production, it is enough to do this once on one sample to figure out what the internal load capacitors should be configured for. Once the optimal load capacitance is found the load capacitors can be configured in the firmware, using the devicetree:

&hfxo {
      load-capacitors = "internal";
      load-capacitance-femtofarad = <...>;
};

&lfxo {
      load-capacitors = "internal";
      load-capacitance-picofarad = <...>;
};

 

Best regards,

Bendik

[Michael_C]

Hi! Thank you very much for the reply! All well noted!

Best regards.