SWRA122D January   2007  – September 2018 CC1100 , CC1100E , CC1101 , CC1101-Q1 , CC1110-CC1111 , CC1131-Q1 , CC1151-Q1 , CC430F5123 , CC430F5125 , CC430F5133 , CC430F5135 , CC430F5137 , CC430F5143 , CC430F5145 , CC430F5147 , CC430F6125 , CC430F6126 , CC430F6127 , CC430F6135 , CC430F6137 , CC430F6147

 

  1.   CC11xx Sensitivity Versus Frequency Offset and Crystal Accuracy
    1.     Trademarks
    2. 1 Abbreviations
    3. 2 Receiver Channel Filter Bandwidth and Crystal Inaccuracies
    4. 3 PER Versus Frequency Offset
    5. 4 Crystal Accuracy
    6. 5 Sensitivity Versus Frequency Offset
      1. 5.1 4.8 kbps
      2. 5.2 10 kbps
      3. 5.3 38.4 kbps
      4. 5.4 250 kbps
      5. 5.5 500 kbps
  2.   Revision History

4 Crystal Accuracy

Section 5 shows plots of sensitivity versus frequency offset for different data rates. The required crystal accuracy is calculated from the total frequency offset as

Equation 2. Total frequency offset = 4 × XTALppm × fRF
Equation 3. Crystal accuracy (in ppm) = Total frequency offset × 1E6 / (4 × fRF)

Table 1. Crystal Accuracy Requirement for Selected Data Rates and Modulation Formats With FOCCFG.FOC_LIMIT[1:0] = 11b

Case Figure 3-dB Bandwidth (Total Frequency Offset) Crystal Accuracy (868 MHz)
4.8 kbps, 2FSK, 25 kHz deviation, DC filter,
RX filter bandwidth = 101  kHz		 Figure 4 50 kHz ±14 ppm
4.8 kbps, 2FSK, 25 kHz deviation, no DC filter,
RX filter bandwidth = 101 kHz		 Figure 5 50 kHz ±14 ppm
10 kbps, 2FSK, 19 kHz deviation, DC filter,
RX filter bandwidth = 101  kHz		 Figure 6 70 kHz ±20 ppm
10 kbps, 2FSK, 19 kHz deviation, no DC filter,
RX filter bandwidth = 101 kHz		 Figure 7 70 kHz ±20 ppm
38.4 kbps, 2FSK, 20 kHz deviation, DC filter,
RX filter bandwidth = 101  kHz		 Figure 8 110 kHz ±32 ppm
38.4 kbps, 2FSK, 20 kHz deviation, no DC filter,
RX filter bandwidth = 101 kHz		 Figure 9 120 kHz ±35 ppm
76.8 kbps, 2FSK, 32 kHz deviation, DC filter,
RX filter bandwidth = 232  kHz		 – 230 kHz ±66 ppm
76.8 kbps, 2FSK, 32 kHz deviation, no DC filter,
RX filter bandwidth = 232 kHz		 – 260 kHz ±75 ppm
100 kbps, 2FSK, 47 kHz deviation, DC filter,
RX filter bandwidth = 325  kHz		 – 220 kHz ±63 ppm
100 kbps, 2FSK, 47 kHz deviation, no DC filter,
RX filter bandwidth = 325 kHz		 – 180 kHz ±52 ppm
250 kbps, MSK, DC filter,
RX filter bandwidth = 541  kHz		 Figure 10 200 kHz ±58 ppm
250 kbps, MSK, no DC filter,
RX filter bandwidth = 541 kHz		 Figure 11 220 kHz ±63 ppm
500 kbps, MSK, DC filter,
RX filter bandwidth = 812  kHz		 Figure 12 120 kHz ±35 ppm

NOTE

The ADC spectrum in the RX chain consists of a significant DC component. This puts a lower limit on the IF frequency that can be used. For optimum sensitivity, a digital DC filter can be enabled (MDMCFG2.DEM_DCFILT_OFF =0), and the ADC DC output is attenuated. This opens for selection of lower IF frequencies thereby lower noise floor and improved sensitivity. As an example, for 868 MHz, 250 kbps 2-FSK, enabling the DC filter gives 2 dB better sensitivity, at the expense of an increased current consumption of 2.3 mA.