nRF52840 Direct Test Mode carrier frequency tolerance failure

[irarykim]

Hi,

We got carrier frequency tolerance failure in a certification test.

The max deviation should be under 20ppm, but the result is above 30.

We used DTM example in nRF5 SDK v16.0.0.

Is there any modification I can do to reduce carrier frequency tolerance?

(We use 32MHz External Crystal)

Thank you.

Jason

[Bendik Heiskel]

Hello Jason,

A large deviation in carrier frequency is a result of a incorrectly loaded 32MHz crystal.To correct this the values of the load capacitors must be changed.

We have a white paper that outlines the crystal oscillator design considerations: https://infocenter.nordicsemi.com/pdf/nwp_015.pdf?cp=17_14

 

Best regards,

Bendik

[irarykim]

Hello Bendik,

We tried as you said and found a better capacitor value! Now we are waiting for the result from certification lab. I will close this ticket after it is resolved. 

Thank you.

Jason