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WL1837MOD: Same layout in different board require C1PC?

Lao Hu
Intellectual 790 points

Part Number: WL1837MOD

Hi All,

A custom board is designed including the WL1837MOD. The layout was replicated from the WL1837MODCOM8I, as much as possible. Basically, the only difference so far is that the custom board is 8 layers.  already gave us detail info about the stack, including the 4 layer board with a width of 1.52mm. Joseph Gigi (1304335) also recommended to use the same length as reference board. Other post as been related as well. However, I still have a question. If I keep the same trace width as original, the impedance will be incorrect because the stack-up layer is different, even if I use a 4 layer board, the manufacturing process could bring different results. 

So, assuming that I need to integrate the WL1837MOD in a 8 layer stack-up 1.58mm (already verified with the manufacturer):

  1. May I change the RF width trace to get a 50ohm impedance (in this case to 5mil width) with exactly the same distance. The original is 16mil. 
  2. May be have other issues missing according with the PCB as show the picture?

The project still have margin to change locations in the final board, and this module is on top priority if a change is required.

Thanks for your feedback,

Julio

  • 0
    TI__Mastermind 29361 points
    Hi,

    Your query has been assigned to relevant experts. We will get back to you shortly.

    Best regards,
    Vihang
  • 0
    TI__Genius 13710 points
    Hi Julio,

    if your stackup is different, then you will need to modify the RF trace width to be 50 ohms. In terms of C1PC, this should be fine and I do not see an issue with what you are doing. I assume you are using the same Antenna s well. Ensure that you have also modified the matching network to tune the antenna based on your final application.

    We always recommend that you consult with your regulator test house as they can confirm that indeed it is only a C1PC. Also safety and radiated tested are something that needs to be done at the system level so you will want to check again to see what additional test may be required.

    I hope this helps.

    Thanks,
    Riz
  • 0 in reply to Rizwan Murji
    Intellectual 790 points

    Hi Vihang, Riz,

    Thanks for your feedback, very appreciated. 

    As you suggest, I will tune the final board and check with my regulator for additional testing. 

    A last question about the integration of the WL1837MOD in portable devices. According with the certification guide, this device (tablet) need to perform a SAR test for RF exposure evaluation. Once this test is performed, please, may I know the recommendation to adjust these results in case of over limits? Software or Hardware? And, this adjustment will affect the C1PC?  

    Thanks again,

    Julio