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LAUNCHXL-CC1312R1: Adapting the operation frequency of the board to 434 MHz

Mehrdad Ghanad
Prodigy 10 points
Part Number: LAUNCHXL-CC1312R1

Hello,

I like to modify the matching network of the LAUNCHXL-CC1312R1 to optimize its output power and sensitivity for 434 MHz operation.

 According to “CC13xx/CC26xx Hardware Configuration and PCB Design Considerations”, we need to use reference design of LAUNCHXL-CC1352P-4 to tune the dev kit to 434 MHz. The following figure shows the matching section of the LAUNCHXL-CC1352P-4.

According to this schematic, we have updated the matching network of the LAUNCHXL-CC1312R1 according to the following table.

Component

Value

L11

18 nH

L12

100 nH

L32

18 nH

L33

18 nH

L34

15 nH

C11

7.5 pF

C21

7.5 pF

C31

470 pF

C33

4.7 pF

C34

15 pF

C35

7.5 PF

C37

470 pF

 

However, when we use RSSI for checking the power of received signal we see that the sensitivity of the board is degraded by 20-30 dB compared to a board with original matching network but operating at 434 MHz.

Many thanks in advance to let us know, if the components we used to update the matching network of LAUNCHXL-CC1312R1 for 434 MHz operation is correct? And what would be the potential other reasons for the degraded sensitivity?

  • 0
    TI__Mastermind 30890 points

    Hi,

    Are you using 0201 or 0402 ?

    Make sure to use the same passive size that was used in the original design at 434 MHz.

  • 0 in reply to RGW
    TI__Mastermind 30890 points

    20-30 dB is a huge degradation on the Rx side. Just double check the soldering and a quick sanity check by measuring the conducted unmodulated Tx output power as well.

  • 0 in reply to RGW
    Prodigy 10 points

    We are using 0402 components for the matching network components.

  • 0 in reply to Mehrdad Ghanad
    Prodigy 10 points

    So the modification of the components as I proposed above for 434 MHz operation is correct?

    If this is the case, we will investigate the soldering quality and also perform conducted measurements of the output power

  • 0 in reply to Mehrdad Ghanad
    TI__Mastermind 30890 points

    CC1352 used 0201 passive size so there could be some deviation here due to 0402 is being used instead of 0201 but this can not count for 20-30 dB delta.

    Let me know when you have measured the conducted output power.

  • 0 in reply to RGW
    Prodigy 10 points

    We did some conducted output power measurements with original matching network and matching network updated for 434 MHz operation. Output of the devkit is measured with spectrum analyzer using RF cable. There is 40 dB attenuator at the input of the spectrum analyzer to avoid the device saturation. The following table shows the measured output power for different output power settings for the original board and the board with updated matching network. The attenuation of the 40 dB attenuator is already deducted from data in the following table. The boards are set to send CW tone.

    Even that I am not sure about the accuracy of measured output power level as measurements are done with our partner, from the following table we can conclude that the updated matching networks seems to be working at 434 MHz.

    Thanks to let me know your inputs and following steps to debug the issue?

     

    Frequency (MHz)

    Output power (dBm)

     

    Expected

    Original matching network

    Modified matching network

    868

    -20

    -14.5

    -42.5

    868

    10

    13.5

    -17.5

    868

    14

    16.5

    -15.5

    434

    -20

    -9

    -14

    434

    10

    13.5

    14

    434

    14

    16

    18.5
  • 0 in reply to Mehrdad Ghanad
    TI__Mastermind 30890 points

    Hi,

    The values you posted previously are correct for a 0201 passive size but these are not correct for 0402. According to your measurements you are measuring a high Tx output power which also suggest the match is incorrect. Even if the Tx output is approx 4 dB too high this will have a negative effective on the Rx side. The RF network is always optimized for optimum link budget with Tx and Rx. So if you are measuring 4 dB too much on Tx then the Rx degradation will be much larger than 4 dB.

    Suggest you use the following passive values instead for 433 MHz operation. These have been based upon 0402 and not 0201.

    Let me know if this resolves the issue.

  • 0 in reply to RGW
    Prodigy 10 points

    Hello,

    Many thanks for the proposed matching network, we will update our DevKit with the proposed components.

    We also did conducted RSSI measurements, where you can find the results in the following table. From conducted measurements it does not seem that the sensitivity of the updated matching network is degraded for 434 MHz operation, we will try to do sensitivity measurements.

    Frequency (MHz)

    RSSI (dBm)

     

    Expected

    Original matching network

    Modified matching network

    434

    -49

    x

    -49

    434

    -54

    -55

    x

    434

    -64

    x

    -63

    434

    -69

    -70

    x

    434

    Noise floor

    -100

    -104