CC2541: Range issue

Hello Felicita,

The most common reasons for degraded RF range are poor layout and/or not following the reference design. I would start by taking conducted RF measurements with SmartRF Studio 7 to check for unexpected frequency deviations, then perform RF-PHY PER testing. If conducted measurements are good, then it's likely an antenna issue.

Best wishes

Dear JXS,

Thank you for your inputs.

We tested using SmartRF Studio. We observed PER to be high in few frequencies.

We also observed that changing the crystal's load capacitance gave improved range in one particular board up to 40 meters.

We are stuck on how to overcome this issue.

Your inputs will help a lot!

Regards,

Felicita Mercy D.

Hello Felicita,

In the absence of a layout, my advice would be to compare your board to our reference design.

Otherwise, if you can provide your layout of the RF power, clk & ground, that would be helpful.

Best wishes

Dear JXS,

Thank you!

Can you please share your email ID for sharing the layout details.

On further testing, we observed that our boards are able to advertise till 40 meters, but unable to connect.
Will this clue be useful for any conclusion?

Regards,
Felicita Mercy D.

Hi Felicita,

If they are unable to connect at distance you could have an issue with poor RX performance. This can be caused by poor RF layout and potentially noise sources on your board.

If you are unable to connect at all it could be due to inaccurate 32 kHz clock.

Regards,
Fredrik

Hi Fredrik,

We tried tuning 32kHz clock and replaced the crystal too. We are still finding issue in connecting (takes too long to connect, or doesn't connect at all).
Advertising works more than 30 meters, but RSSI sometimes shows less than -90 in few meters (not always).

Regards,
Felicita Mercy D.

Hi Fredrik,

The CC2541 datasheet mentions the crystal load capacitance to be 10pF to 16pF. The crystal we use has 8pF CL (CX2520DB32000D0FLJCC). Will this have any adverse effect on BLE?

Regards,
Felicita Mercy D.

Hi Felicita,

Using a crystal with too low CL in itself may not affect BLE communication directly. The only concern with this is that the oscillator can fail to start in certain conditions. In which case the device will hang completely.

Another question is whether the load capacitors have the right value or not. With a 8 pF crystal I would expect your caps to be 10 - 12 pF is that the case? If these are off, you will get a frequency offset on the RF carrier which may affect the communication.

Cheers,
Fredrik

Dear Fredrik,

Thank you very much for your information.

My capacitors on board are 12pF.

Regards,

Felicita Mercy D.