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Original question:

CC1310: CC1310 Frequency Offset

CC1310: Coherent vs Non-Coherent Detection and frequency ramping

Maaz Awan
Prodigy 155 points
Part Number: CC1310

Greetings Forum!

The other day, I came across the text apropos Phase Locked Loop Filter Design for a synchronization task I was conducting for some other project and I realized that we missed a trick or two when we were concerned about the offset in frequency in my following thread:

CC1310 Frequency Offset

. I would like to explain the whole situation and request possible way forwards or alternate solutions for the task at hand. I have broken down my problem into the following argument.

Does the CC1310/1312 employ coherent or non-coherent detection for GFSK demodulation? If it is coherent, what are the characteristics/order of loop filter in the PLL? Is it designed to have an upper-bound on the steady state error if the incoming signal has frequency ramp? The frequency offset is increasing linearly with time. The maximum rate of this ramp is not known yet but the slope can be provided later.

To the best of my understanding, a PLL trying to lock to the phase of an incoming signal in a coherent detection may warrant a higher order loop filter.[Digital Communications, Bernard Sklar, Chaper 10 Synchronization].

If say there is no way for the existing PLL to overcome a frequency ramp in the incoming signal, can you suggest an alternate radio that may employ non-coherent detection and frequency lock may be sufficient for demodulation.

Looking forward to your valuable feedback and comments.

Best Regards

Maaz Ali Awan

  • 0
    TI__Mastermind 20407 points

    Hi Maaz,

    I have assigned the thread to our RF experts, they should get back to you soon. 

    Regards,

    Sid

  • 0
    TI__Mastermind 31730 points

    Hi,

    What are the actual issues you are facing with your application to suggest the current implementation is not optimum? 

    Changing topologies and modem design is not so straight forward and cannot be discussed on an open forum for obvious reasons.

  • 0 in reply to Sid
    Prodigy 155 points

    Greetings  

    Thank you so much sir!

  • 0 in reply to RGW
    Prodigy 155 points

    Greetings Mr RGW!

    Thank you for getting back on the issue. Actually the issue was frequency offset as already mentioned in my related post however it turns out now that despite the frequency offset being catered in the extended bandwidth, the problem seems to occur when the mini-drone carrying the CC1310 as a receiver tends to accelerate. This lead me to beleive that perhaps the said radios are not designed to cater acceleration between communicating nodes.As I understand this relative acceleration is causing a frequency ramp beteen transmitter and receiver. Please guide me through this issue.

    Best Regards

  • 0 in reply to Maaz Awan
    TI__Mastermind 31730 points

    Hi,

    Thanks for explaining the issues you are facing with your application. We have several customers that use drones, sport applications with inbuilt RF and sensors that works fine with acceleration. I do not believe this is related to the modem/PLL configuration. Some ideas to pursue for debugging: 

    Have you measured the frequency offset with a static Tx unmodulated carrier for both the transmitter DUT and receiver DUT ?

    Do you have the same type of crystal in these DUTs ?

    Just for debugging purposes. Have you tried at another frequency several MHz away from current frequency to see if there could be an external RF noise causing the issue?

    Just for debugging purposes. Have you tried disabling the DCDC converter to see if you still experience similar behavior ?

    The control for the acceleration, has this been monitored in the lab with a decreased RF level until the RF link budget is broken ?

  • 0 in reply to RGW
    Mastermind 6160 points
    Maaz Awan said:
    the problem seems to occur when the mini-drone carrying the CC1310 as a receiver tends to accelerate.

    Have you tried to calculate the actual frequency shift this will cause? I would assume  that the shift is insignificant. I would look at other causes. One thought, have you looked at power noise and how this impact the CC1310? If you mount the drone in the lab and increase the speed of the motor, do you see the same issue then? Is the sensitivity impacted of how the motor is operated?