nRF52832 FCC failed

[Ye-Sheng]

Hi,

We're designing a BLE module, which is fairly straightforward. The design contains a nRF52832 + SKYWORKS SKY66403-11 FEM. We set the nRF52832 to transmit at -4 dBm and the SKY66403-11 is configured to have 22 dB gain.

When we test the FCC, we failed the unwanted emission. We have a peak located at the 128 MHz below center frequency.

Does anyone have related experience or any suggestions?

Thanks,

[Andreas]

Hi,

 

This is a harmonic originating from the clock system. You can try to enable ICACHE and populate 100 nF on DEC2, this should reduce the level of it by a couple of dB.

 

Best regards,

Andreas

[Ye-Sheng]

Andreas,

Thanks for your suggestion. We tried to populate 100 nF on DEC2, but the result remains the same. The above plot is measured with ICASH on already. It gets worse if we turn off ICASH indeed.

Further things we can try?

Thanks,

Ye-Sheng

[Andreas]

Hi Ye-Sheng,

 

The pattern you see should be much more constant, no ripple in the level. There is a component at -128 MHz, but it should not be this high, it might be that the ripple level builds on top of this. Have you measured the output of the nRF52 to determine if it originates from the nRF52 or the FEM?

 

Best regards,

Andreas