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Original question:

CC1200: Calibration does not work between 40°C & 55°C

CC1200: CC1200 - 625ksps 4GFSK maximum frequency deviation setting

Pawan Ghotikar
Expert 1140 points
Part Number: CC1200

Hi,
We are experimenting with 625ksps 4GFSK with fc=169MHz and Fxtal = 40MHz, Power = 0dBm, high performance mode. Can someone assist me with maximum frequency deviation setting? Also, is there any setting in particular to be careful about?

Thanks,
Pawan

  • 0
    TI__Guru 73361 points

    Hi Pawan,

    In general I would recommend you to follow the data sheet. I have assigned someone to answer your question, please expect follow-up next week.

    Cheers,

    Marie H

  • 0
    TI__Genius 10305 points

    Hi Pawan,

    There are several factors that can affect this. You are likely already doing this but experimenting using SmartRF Studio 7 will be useful here as it will flag combinations that are not possible with an error.

    Maximum f_dev

    Looking at Section 12 (Register Descriptions) of SWRU346B (CC120X Low-Power High Performance Sub-1 GHz RF Transceivers (Rev. B)): https://www.ti.com/lit/ug/swru346b/swru346b.pdf the maximum f_dev = ~1.2 MHz for both DEV_M and DEV_E.

    Modulation Index

    However, there are other factors to consider. For 4-GFSK the modulation index for inner symbols should be >= 1/3. Lower modulation index will degrade sensitivity significantly.

    Receiver Bandwidth

    Probably the main factor is your RX BW.

    RX BW > SBW + (4 * XTALppm * RF Frequency of Operation)
    Your Signal Bandwidth (SBW):
    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
    SWRA122D (CC11xx Sensitivity Versus Frequency Offset and Crystal Accuracy) may be helpful if you need more clarification on this: https://www.ti.com/lit/an/swra122d/swra122d.pdf (although this is for the CC11xx the same principle of accounting for crystal frequency error applies).
    As you widen your RX BW, the higher the Noise Floor will be, so your Sensitivity will be degraded. What is acceptable will depend on your application.

    Maximum RX filter BW

    Note that (from SWRU346B): The RX filter BW should never be set higher than 1666.7 kHz.

    Other Useful Resources

    You may also find SWRA682 (Finding Settings for New Phys for the CC13x0 and CC13x2 Family) useful (even though it is written for another family of CC devices a lot of the same principles apply): www.ti.com/.../swra682.pdf
    Table 2 in SWRA479A (Achieving Optimum Radio Range): https://www.ti.com/lit/an/swra479a/swra479a.pdf lists Sensitivity levels for various devices and data rates.
    Regards,
    Zack