CC2640R2F: Communication Range is too short

Hello Cary,
Which module is this? Your own custom module?
Have you copied the reference design as closely as possible and matched the RF path to the antenna?

You can use: www.ti.com/.../rf-range-estimator to see how the radio parameters impact on the expected range. Typically a 6 dB difference in link budget is x2 in range.

From the numbers presented it looks like you need to look into the sensitivity on your board.

Why do you use a 12 pF load cap on the xtal, does that mean you disable the internal load cap array?

Dear Eirik,
Thanks for your quickly response.
It's our customer's module. Customer has copied the reference design as closely as possible, but used External antenna.
Parameters of external antenna as below:
Wireless standard : IEEE 802.11n and 802.11 a/b/g
Frequency range : 2.4~2.49GHz ; 4.9~5.9GHz
Peak gain : 1.5 dBi @2.44 GHz; 3.1 dBi @ 5.2 GHz
VSWR 2:1
Impedance: 50 Ohm
Processing capacity: 30 dBm
Interface: U.FL connector (I-PEX); 50Ohm, 1.13MM diameter RF out line
Is there any comments on used external antenna? Thanks!

Dear TER,
Thanks for your infomation too.
The reception sensitivity is indeed a little worse. Customer used external antenna to test. Any more infomation about used external antenna
and how to design antenna?

For load capacitance, in accordance with the reference design, the frequency offset is more than 100K without load capacitance .
Used 2pcs 12pF capacitance on the xtal , frequency offset changed to less than 20K, compliance with the requirements.

Which xtal (exact spec) are you using? 100 kHz offset with default load cap sounds a bit high.

I assume that the sensitivity measurements you have done is conducted. If that is the case I suggest trying to figure out what cause the poor sensitivity before looking into antenna design.

Dear TER,
SMD SEAM SEALING X'TAL 2.5 × 2.0 (TXC) is used, Frequency: 24MHz; Load Capacitance 10pF; Equivalent Series Resistance 60Ω.
What needs to be solved is to improve the receiving sensitivity. Please recheck, thanks!

Note that according to 5.14 in www.ti.com/.../cc2640r2f.pdf the xtal is out of spec.

For a test, try on the the xtals listed here: processors.wiki.ti.com/.../CC26xx_Crystals without external loadcaps and see if it improves.

Dear TER,
Thanks！
With external xtal and use load capacitance 12pF, frequency offset has been changed to less than 20K, compliance with the requirements.
So we think that what needs to be solved is to improve the receiving sensitivity.
I will ask customer to change the xtal to test first.

The xtal should still be within spec to ensure good performance in production.

Dear Ter,
Customer has changed the xtal (use EVM xtal) to test. The result is: Frequency offset is less than 20K, but the receiving sensitivity is still about -88dbm, no relation to the xtal.
Would you please help to analysis how to improve sensitivity ? Thanks!

To be able to say why you get poorer sensitivity than expected I would need to see the schematic and layout (you can send them as a private message)

One thing you can look into first: Since the output power is as expected but not the sensitivity, look into the DCDC. Try to turn off the DCDC and run only on the internal LDO and see if that changes anything.

Hi,

From my experience and testing if you set this define below wrong at your board file, the connection distance is short and will disconnect.

/*
 *  ============================================================================
 *  RF Front End and Bias configuration symbols for TI reference designs and
 *  kits. This symbol sets the RF Front End configuration in ble_user_config.h
 *  and selects the appropriate PA table in ble_user_config.c.
 *  Other configurations can be used by editing these files.
 *
 *  Define only one symbol:
 *  CC2650EM_7ID    - Differential RF and internal biasing
                      (default for CC2640R2 LaunchPad)
 *  CC2650EM_5XD    – Differential RF and external biasing
 *  CC2650EM_4XS    – Single-ended RF on RF-P and external biasing
 *  CC2640R2DK_CXS  - WCSP: Single-ended RF on RF-N and external biasing
 *                    (Note that the WCSP is only tested and characterized for
 *                     single ended configuration, and it has a WCSP-specific
 *                     PA table)
 *
 *  Note: CC2650EM_xxx reference designs apply to all CC26xx devices.
 *  ==========================================================================
 */
#define CC2650EM_7ID

-kel