CC2640R2F: The RX sensitivity of CC2640 is abnormal, please help to locate

leo chen

Part Number: CC2640R2F

Test the rf index of CC2460, the test point is balun unbalanced port, the transmission power is 3.17dbm(configured as 5dbm), the sensitivity is only -88dbm, far lower than the specification -97dbm, may I ask what is the problem caused by this, thank you!

note:Medium for FPC, double - layer board

over 6 years ago

0 Hank Zhang over 6 years ago

Expert 2040 points

Part Number: CC2640R2F

Test code:host_test

The instrument:CMW270

Five boards were tested,sensitivity is only -88~-90dBm，What could be the reason

0 J Lindh over 6 years ago

TI__Guru 57865 points

Hi Leo,
Have you followed the reference design?

0 TER over 6 years ago in reply to J Lindh

TI__Guru**** 317180 points

You can start by go through www.ti.com/.../swra640a.pdf

0 Fredrik K over 6 years ago

TI__Guru** 106705 points

Hi Leo,

You balun layout is not according to our reference design and can be the source of the issues you are seeing.

Can you also share a snippet of your botton layer?

Regards,
Fredrik

0 Fredrik K over 6 years ago in reply to Fredrik K

TI__Guru** 106705 points

Hi Hank,

I merged your post into this thread since it is about the same issue.

Now that I can see the bottom layer, it is obvious that the layout is the source of the poor RF performance here. Basically, all the VDD traces are blocking ground return currents. The most concerning is the VDDR trace splitting the ground plane between the IC ground vias and the RF path, but there are also several decoupling caps with poor ground connection to the IC.

To resolve the issue, a new layout must be done following the guidelines in the application note TER is linking to. With a 2-layer PCB, I would highly recommend moving as much as possible of the traces, including VDD, to the top layer.

Regards,
Fredrik

0 leo chen over 6 years ago in reply to Fredrik K

Prodigy 235 points

hi，Fredrik

Thank you for your help. I can understand that the reason of poor sensitivity is caused by noise, so it has almost no influence on the transmission power

0 leo chen over 6 years ago in reply to leo chen

Prodigy 235 points

the transmission power is 3.17dbm(configured as 5dbm),it is OK

0 Fredrik K over 6 years ago in reply to leo chen

TI__Guru** 106705 points

Hi Leo,

It is not noise, but rather that the RF impedance is not correct due to poor ground connections.

The output power is also a bit on the low side, although not as off as the sensitivity.

Regards,
Fredrik

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CC2640R2F: The RX sensitivity of CC2640 is abnormal, please help to locate