CC2650: Custom board with bad Rx performance

Vipin Sharma39

Part Number: CC2650
Other Parts Discussed in Thread: , CC2640

I have a CC2650 4x4mm based custom board with simple_peripheral example running. Everything on the board works fine; I am able to connect, transmit and receive. There is however one issue which I don't understand with respect to Rx performance.

When the board is advertising I have good enough range (say 10ft indoors). But when the board connects to the a CC2650STK based evaluation module running simple_central, I cannot have more than 10cm distance between the custom board and the CC2650STK board.

The fact that the advertising mode has good range (only Tx on the custom board is On) but an established connection (required both Tx/Rx) has less than 10cm range, it tells me that something is off with the Rx performance of the board. How do I figure out what is going on?

I have attached the RF layout of the board along with schematic. The CC2650 device is configured with internal bias differential input RF signal chain.

over 9 years ago

0 RachelP over 9 years ago

TI__Genius 12815 points

Hi Vipin,

Have you gone through the Hardware Design resources on the TI BLE Wiki? http://www.ti.com/ble-wiki

0 JXS over 9 years ago

TI__Guru** 105180 points

Hello Vipin,

Your symptoms are consistent with a misconfigured RF Frontend and Bias configuration that we describe in the pinned CC2640 FAQ post as well as on the HW bringup article on the TI BLE Wiki.

Did you modify any project preprocessor settings? Can you confirm the following build option is selected in ble_user_config.h at build time:

#define RF_FE_MODE_AND_BIAS ( RF_FE_DIFFERENTIAL | \
RF_FE_INT_BIAS)

Best wishes

0 Fredrik K over 9 years ago

TI__Guru** 106705 points

Hi Vipin,

Your layout is extremely bad, it is not surprising that you are not getting the expected performance. In RF proper layout is very important, it is not just a matter of making the right connections. We have some guidelines on our wiki which I suggest you read through:
processors.wiki.ti.com/.../CC26xx_HW_training_Layout_Considerations.pdf
processors.wiki.ti.com/.../CC26xx_HW_Checklist

Cheers,
Fredrik

0 Vipin Sharma39 over 9 years ago in reply to Fredrik K

Intellectual 500 points

Thanks Fredrik for the pointer. I will follow these guidelines in the next revision of the board. For now, my prototype works much better once I fixed the differential RF front end and internal bias setting in the firmware. It turns out my firmware settings were pointing to single ended external bias.

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CC2650: Custom board with bad Rx performance