SWRA682 December   2020 CC1310 , CC1312PSIP , CC1312R , CC1314R10 , CC1350 , CC1352P , CC1352P7 , CC1352R

 

  1.   Trademarks
  2. 1 Introduction
  3. 2 Recommended Test Setup
  4. 3 Overrides
  5. 4 Find the Needed RX BW
  6. 5 How to Set the Deviation
  7. 6 Theoretical Sensitivity
  8. 7 Determine AGC_REF Level
  9. 8 Determine Anti-Aliasing BW
  10. 9 Determine PA Ramp Settings
  11. 10Intermediate Frequency (IF)
  12. 11LNA Ib Offset
  13. 12Sensitivity and Selection of Sync Word
  14. 13Narrowband
    1. 13.1 Frequency Offset Tolerance
    2. 13.2 Low Datarate
    3. 13.3 Phase Noise
  15. 14RSSI Offset

13.1 Frequency Offset Tolerance

According to Equation 2, XTALppm has to be set low if the wanted signal bandwidth is close to the wanted RX BW to be able to receive. In some cases it is not possible or wanted to decrease XTALppm to the extent that the equation dictates. An alternative is to use “Feedback to NCO(1)” (FB2NCO), which increases the effective RX BW without increasing the noise BW which determines the sensitivity limit. In other words, it is possible to increase the frequency error tolerance without degrading sensitivity.

For the CC13x0 family, FB2NCO is controlled with:

HW_REG_OVERRIDE (0x52AC, <value>)

For the CC13x2 family, FB2NCO is controlled with:

HW_REG_OVERRIDE(0x5320,<value>)

Where <value> is a 32 bit register but only the 16 LSB bits are used.

  • Enable FB2NCO frequency offset compensation (FOC) mode by setting bit[13]=1
  • Disable strict sync word check by setting bit[12]=1. Since the strict sync search is turned off it could be required to increase the sync threshold. How to do this is documented in <SDK install path>/docs/proprietary-rf/proprietary-rf-users-guide/proprietary-rf/packet-format.html#sync-word-qualifier.
  • Configure FOC_GAIN[11:8]. Higher value will give larger frequency "correction" steps and might cause a longer settling time.
  • Configure FOC_LIMIT[7:0] for offset regulation
    • The improved BW is given as FOC_LIMIT*NCO resolution. Resolution is RF frequency*LO_DIV/2/12/24/1024/2^bde1
    • Run PER vs level vs offset and check if there is an error floor (aka residual PER) and if the frequency tolerance is acceptable.
    • If an error floor is present the adjustment loop could be made slower by adjusting the IIRGAIN. The IIRGAIN is available through bit[3:1] of < value>: HW_REG_OVERRIDE(0x50EC, <value>) for CC13x0 and HW_REG_OVERRIDE(0x0x50FC, <value>) for CC13x2. The most optimal value has to be found through trial and error.
For FB2NCO to work properly the NCO resolution should be less than half the deviation.

RXBW = chfival / (2^(bde1 + bde2) * 288) * LODIV * RF frequency * 1000/2 where chfi can have one of the following four values: 0.5, 0.33, 0.416, 0.29. chfi[1:0] selects which chfival to use according to the table below:

chfi[1:0] chfival
0 0.5
1 0.33
2 0.416
3 0.29

The following can be done to improve NCO resolution:

Change the values for bde1 and bde2:

  • Set bde1 as high as possible.The max value for bde1 is 4.
  • Add symbolRate.decimMode = 7 as part of the CMD_PROP_RADIO_DIV_SETUP settings.
  • FOC_LIMIT has to be adjusted if bde1 is increased since the "additional" BW is given as FOC_LIMIT * NCO resolution.
  • Check AGC gain after changing bde2 and bde1.
  • When intFreq = 0x8000 the IF is 106/bde1. The performance with the new IF should be verified.

The rxbw setting given as part of the CMD_PROP_RADIO_DIV_SETUP is build up as follows:

Rxbw = 0xbde2[7:5], bde1[4:2], chfi[1:0]

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NCO: Numerically Controlled Oscillator