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FMCOMMS5 Design Files

Question asked by asadi.siyavash on Aug 21, 2017
Latest reply on Aug 24, 2017 by Vinod


I checked Allegro File of fmcomms5, I have a question about CML output of "13617CS". As I checked datasheet of this IC, Outputs are designed to be a broadband match to 50ohm impedance. In the PCB of fmcomms5, designer used 15.5mil trace on top layer. As I calculate its impedance is 50ohm. but rest of trace is in power layer(plane). it is stripline trace GSG, I calculate width for 50 ohm trace with mentioned data, it should be 3.5mil but it is 15.5mil again! even 20mil for "RX_EXT_LO_B" so it has 12 ohm impedance!!!! could you explain why did you use this width? I know that designer has had his own reasons.


any help would be greatly appreciated.