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CC1125 Adjacent Channel Rejection performance

JBD26
Prodigy 170 points
Other Parts Discussed in Thread: CC1125

I'm finding that the ACR performance varies between samples of CC1125. I have one sample that would pass Category 1 with 1dB margin (using GMSK 4.8kbps) but another 5 samples I have tried would fail by between 0.5 - 3.0dB. Is there an explanation for this? I only have samples of the 0x21 version of silicon would the 0x23 version make any difference to ACR?

  • 0
    TI__Mastermind 39860 points

    Table 9 in application note ti.com/lit/SWRA424 gives the expected performance figures @4.8 kbps for different RX filter BW's. Make sure the RX filter BW is set low, that you use FB2PLL (see User Guide and App Note), and that the charge pump current is set to maximum after calibration (FS_CHP = 0x3F).

    Rev 2.1 and 2.3 have the same performance.

  • 0 in reply to Sverre
    Prodigy 170 points

    Thanks. The ACR performance seems to be about 2-3dB worse when I use GMSK and I'm measuring up to 3dB difference between samples. Is this expected? Can any other components influence the ACR performance?

  • 0 in reply to JBD26
    TI__Guru**** 317180 points
    Sorry for delay. I suspect that I have gotten a follow in this request internally. Do you use 4.8 kbps/ 1.2 kHz deviation? And if so are you tied to use this deviation?

    A 3 dB variation between samples sounds to be within what I would expect.
  • 0 in reply to TER
    Prodigy 170 points

    Hi Thanks for the reply. I need to use 4.8kbps/1.2kHz deviation for backward compatibility. It also needs to be Manchester - the actual data rate is 2.4kbps. Do you have any other suggestions to improve the ACR performance using this modulation? Are there any external components that could influence the ACR performance? 

  • 0 in reply to JBD26
    TI__Guru**** 317180 points
    I finally got around to test this is our test system.

    When I test 4.8 kbps, 2.4 kHz dev vs 4.8 kbps, 1.2 kHz dev I see that both the sensitivity and selectivity goes down by 3 dB. Hence it looks like that the ACR performance with your datarate and deviation will be borderline. The settings we have in thwe CAT1 app note is the one giving the best performance.