SWRA495L December   2015  – April 2025 CC1310 , CC1350 , CC2620 , CC2630 , CC2640 , CC2640R2F , CC2640R2F-Q1 , CC2642R-Q1 , CC2650 , CC2662R-Q1

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1 Oscillator and Crystal Basics
    1. 1.1 Oscillator Operation
    2. 1.2 Quartz Crystal Electrical Model
      1. 1.2.1 Frequency of Oscillation
      2. 1.2.2 Equivalent Series Resistance
      3. 1.2.3 Drive Level
      4. 1.2.4 Crystal Pulling
    3. 1.3 Negative Resistance
    4. 1.4 Time Constant of the Oscillator
  5. 2 Overview of Crystal Oscillators for CC devices
    1. 2.1 24MHz and 48MHz Crystal Oscillator
    2. 2.2 24MHz and 48MHz Crystal Control Loop
    3. 2.3 32.768kHz Crystal Oscillator
  6. 3 Selecting Crystals for the CC devices
    1. 3.1 Mode of Operation
    2. 3.2 Frequency Accuracy
      1. 3.2.1 24MHz and 48MHz Crystal
      2. 3.2.2 32.768kHz Crystal
    3. 3.3 Load Capacitance
    4. 3.4 ESR and Start-Up Time
    5. 3.5 Drive Level and Power Consumption
    6. 3.6 Crystal Package Size
  7. 4 PCB Layout of the Crystal
  8. 5 Measuring the Amplitude of the Oscillations of Your Crystal
    1. 5.1 Measuring Start-Up Time to Determine HPMRAMP1_TH and XOSC_HF_FAST_START
  9. 6 Crystals for CC13xx, CC26xx, CC23xx and CC27xx
  10. 7 High Performance BAW Oscillator
  11. 8 CC23XX and CC27XX Software Amplitude Compensation
  12. 9 Internal Capacitor Array for CC23XX and CC27XX
  13. 10Internal Capacitor Array for CC13xx and CC26xx
  14. 11Summary
  15. 12References
  16. 13Revision History

10 Internal Capacitor Array for CC13xx and CC26xx

Overview

The CC26x2 and CC13x2 radios require a 24MHz or 48MHz crystal as a frequency reference. However, spurs at multiples of 48MHz can occur due to the large current flow between the crystal and XOSC tuning capacitors. These spurs can cause interference by creating voltage drops on shared power rails with the PA and VCO. Reducing the XOSC tuning capacitors to zero decreases these spurs by approximately 5dB for the largest spur.

Load Capacitance Considerations

The internal capacitor array is generally sufficient, but for systems requiring compliance with ARIB STD T-108 and Chinese regulations (470–510MHz), as well as when using the +20dBm PA, external crystal loading capacitors are recommended. Setting the internal XOSC tuning capacitors to zero in these cases helps minimize spurs. The system allows for adjustments using an offset value, which can be positive or negative, to fine-tune the capacitance.

Limitations

The internal capacitor array cannot be fully disabled unless the cap-array delta is set at or below the lowest supported value. The actual resulting capacitance includes parasitic contributions, so the lowest setting does not equate to 0pF. To verify oscillator accuracy, an unmodulated carrier wave must be measured using a spectrum analyzer. SmartRF™ Studio can be used for on-the-fly tuning of the load capacitance before finalizing values in software.

Table 10-1 Internal Capacitor Array Delta for CC13XX and CC26XX
Measured Capacitance on Reference Board (pF) CCFG Delta Value for CC13x0/CC26x0 QFN CCFG Delta Value for CC2640R2F WCSP CCFG Delta Value for CC13x1/CC26x1 QFN CCFG Delta Value for CC13x2/CC26x2 QFN CCFG Delta Value for CC13x4/CC26x4 QFN
2.1 < -55 < -28 < -40 < -40 < -40
2.1 -55 -28 -40 -40 -40
2.2 -54 -27 -39 -39 -39
2.3 -53 -26 -38 -38 -38
2.4 -52 -25 -37 -37 -37
2.5 -51 -24 -36 -36 -36
2.6 -50 -23 -35 -35 -35
2.7 -49 -22 -34 -34 -34
2.7 -48 -21 -33 -33 -33
2.8 -47 -20 -32 -32 -32
2.9 -46 -19 -31 -31 -31
3.0 -45 -18 -30 -30 -30
3.1 -44 -17 -29 -29 -29
3.2 -43 -16 -28 -28 -28
3.3 -42 -15 -27 -27 -27
3.4 -41 -14 -26 -26 -26
3.4 -40 -13 -25 -25 -25
3.6 -38 -12 -24 -24 -24
3.7 -37 -11 -23 -23 -23
3.8 -36 -10 -22 -22 -22
3.9 -35 -9 -21 -21 -21
4.0 -34 -8 -20 -20 -20
4.1 -33 -7 -19 -19 -19
4.3 -32 -6 -18 -18 -18
4.4 -31 -5 -17 -17 -17
4.5 -30 -4 -16 -16 -16
4.6 -29 -3 -15 -15 -15
4.7 -28 -2 -14 -14 -14
4.8 -27 -1 -13 -13 -13
5.0 -26 0 -12 -12 -12
5.1 -25 1 -11 -11 -11
5.2 -24 2 -10 -10 -10
5.3 -23 3 -9 -9 -9
5.5 -21 4 -8 -8 -8
5.6 -20 5 -7 -7 -7
5.8 -19 6 -6 -6 -6
5.9 -18 7 -5 -5 -5
6.1 -17 8 -4 -4 -4
6.2 -16 9 -3 -3 -3
6.4 -15 10 -2 -2 -2
6.5 -14 11 -1 -1 -1
6.7 -13 12 0 0 0
6.8 -12 13 1 1 1
7.0 -11 14 2 2 2
7.1 -10 15 3 3 3
7.3 -9 16 4 4 4
7.4 -8 17 5 5 5
7.6 -7 18 6 6 6
7.7 -6 19 7 7 7
7.9 -5 21 8 8 8
8.2 -4 22 9 9 9
8.4 -3 23 10 10 10
8.6 -2 24 11 11 11
8.8 -1 25 12 12 12
9.0 0 26 13 13 13
9.2 1 27 14 14 14
9.4 2 28 15 15 15
9.6 3 29 16 16 16
9.8 4 30 17 17 17
10.1 5 31 18 18 18
10.3 6 32 19 19 19
10.5 7 33 20 20 20
10.7 8 34 21 21 21
10.9 9 35 22 22 22
11.1 10 36 23 23 23
11.1 > 10 > 36 > 23 > 23 > 23