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TUSB213: Differential signal pattern

Part Number: TUSB213

Hi Team,

My customers have questions about the signal lines of application notes.

Tell me about 2 points about Figure 2. Serpentine Trace Geometry described in High-Speed Layout Guidelines for Signal Conditioners and USB Hubs.

1. Why is it possible to eliminate the influence on impedance by making it like Figure 2. Serpentine Trace Geometry?

2. If it is not possible to comply with the provision of 4.11 Signal Bending on P22, it seems that radiation noise will be affected, but please tell me the reason why it will be affected.

If you have any reference material to the above, please provide the information.

Best Regards,

Kenji

  • Kenji-san

    1. For coupled differential trace structure, it is imperative that both traces in the differential pair maintain the same impedance and the same trace
    length. When one trace is long than the other trace, then you have to use the serpentine method to match the trace length, but you also do not want to create impedance discontinuity. So the Figure 2 method is recommended to match the trace length, but also keep the impedance discontinuity to be within +/-10% tolerance range.

    2, When gradually curved bend is not possible, it will create a impedance discontinuity in the the transmission line because the local increase in effective line width going through the bend. When you have a impedance discontinuity, this will become the source of radiation noise.

    Thanks
    David