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

4 Find the Needed RX BW

The transmitted signal will have a certain signal bandwidth (SBW), which depends on the symbol rate and modulation format. This bandwidth can be approximated by Carson's rule given that the modulation format is FSK:

Equation 1. SBW = 2∗fm + 2∗fdev

Where

  • fm is the highest modulating frequency. 2 ∗ fm = symbol rate
  • Fdev is the frequency deviation. 2∗fdev = frequency separation

Since GFSK uses a shaping to reduce the side lobes the GFSK signal bandwidth will be less than estimated by Carson’s rule. The exact signal bandwidth can be measured with a spectrum analyzer.

On the receiver side there is an RX channel filter, which is centered on the down-converted received RF frequency, such that, the intermediate frequency (IF). The RX filter has a programmable bandwidth (RX BW). The transmitted signal bandwidth has to be less than RX BW, but the frequency error of the transmitter and receiver must also be taken into account.

If there is an error in the transmitter carrier frequency and the receiver LO frequency, there will also be an error in the IF frequency. For simplicity assume the frequency error in the transmitter and receiver is equal (same type of crystal). If the receiver has an error of –X ppm and the transmitter has an error of +X ppm the IF frequency will have an error of +2*X ppm. Conversely, if the receiver has an error of +X ppm and the transmitter an error of -X ppm the IF frequency will have an error of -2*X ppm.

RX BW has to be larger than the maximum SBW plus the maximum frequency error due to crystal inaccuracies. Worst case scenario will be for the crystal errors on TX and RX side to be of opposite signs.

Equation 2. RX BW > SBW + 4∗XTALppm∗fRF

where

  • XTALppm is the total accuracy of the crystal including initial tolerance, temperature drift, loading, and ageing
  • fRF = is the RF operating frequency
Note: There are both a lower and an upper limit on the symbol rate for a given RX BW. The wanted combination of symbol rate and RX BW should be entered in SmartRF Studio. The tool will give an error message if the combination is not possible.