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CC2538-CC2592EM-RD: Different trace widths leading to IFA feedpoint and SMA connector

Steve Raynesford
Prodigy 50 points
Part Number: CC2538-CC2592EM-RD
Other Parts Discussed in Thread: CC2592

The two traces on the output side of the CC2592 are different widths and have different characteristic impedances.  

Both the SMA-connected device and the IFA are 50Ω loads.

1. The trace(s) from C3101 to the IFA are 0.5mm wide with 0.4mm gap over 0.175mm FR4 and simulate at 37 ohms.
2. The alternate trace from C3111 to the SMA connector is half that, at 0.25mm wide with 0.15mm gap and simulates at 54 ohms.

Why are there two different RF trace widths to 50Ω loads?

Thanks
Steve R.

  • 0
    TI__Mastermind 27145 points

    Hi,

    No need to have a 50 ohm line up to the junction of L3104/C3105 Junction. It is better to place the components as close as possible to each other.

    L3104/C3105 is the 50 ohm port. So, the trace from C3111 to SMA connector is matched to 50 ohms.

    Please note that there is a Reference Ground plane underneath the trace from C3111 to SMA connector and no Ground plane underneath the Antenna trace.

    The antenna impedance depends upon the Ground plane, vicinity of the components, size of the board and the Housing of the unit. Any mismatch on the Antenna can be tuned out by using C3109 and C3110.

    We recommend to copy our reference design and use C3109 & C3110 to tune out any mismatch on the Antenna.

    Thanks,

    PM