Frequency Correction on Production Line for each boards to reduce the frequency offset issues

[VishnuPrasad V]

Hi Nordic Team,

We have developed a project with the nrf52840 + nrF21540 FEM for an audio-related application.

We are in Production now. As part of the QC process of the Production house, it is mandatory to measure the RF Frequency Offset and tune it for Frequency correction.

If the Frequency Correction operation is not performed they won't give a guarantee on the RF performance.

So we need help from nordic to support this. We didn't find any relevant documents to do frequency correction on nRF52840.

What we exactly like to get from the nordic team is 

1) Command/ Register to get the current frequency offset tuning of the chipset.

2) Command/Register to Write the new value for tuning the offset.

Thanks!

[Susheel Nuguru]

This is unfortunately not possible to do with this solution.

[Susheel Nuguru]

It should be enough for you to check the frequency of the configured radio and this can be sniffed through radio register. You can try to use nRF5340 to have more advance frequency calibration capabilities

[VishnuPrasad V]

Hi Susheel,

Thanks for the Quick response.

If all the design of HW is done according to how nordic suggested, what is the expected offset range?

Thanks!

[Susheel Nuguru]

I am not 100% sure on this, let me ask my colleague and come back to you today.

[Susheel Nuguru]

Suggestions from our hardware expert

The frequency offset is dependent on the accuracy of the HFXO, this is tuned by changing the load capacitance on each of the XO lines. The values of these capacitors is dependent on the crystal, and may not match the 12pF we have in the reference design. To calculate a good starting point for these values we have a equation in the PS:

Where C1 and C2 are the capacitors needed, Cpin is the pin capacitance listed in the PS, CL is listed in the crystal datasheet, Cpcb1 and Cpcb2 is the trace capacitances.

Assuming 0 trace capacitance and specifying C=C1=C2 the equation can be simplified to:

C = 2*CL-Cpin

This will give a good staring point, but may need to be tuned if the Cpcb cant be neglegted.

We tune this as a part of the radio and antenna tuning, so you can send boards to us if you don't have the equipment needed(spectrum analyzer)