Electronic – What are these wiggly USB 3 traces on the motherboard


picture of oddly shaped traces, with other components for scale

photo of board with additional context

I was taking a look at my motherboard, and I noticed the above traces on the USB 3.0 ports. A bit of prior research:

  • The C34WH IC is probably a SN74LVC2G34 Dual Buffer Gate.
  • Unclear what chip the top two ICs are, but the markings likely read 1188J.

What is the purpose of making these traces like this?

How is the appropriate shape of the traces calculated?

Best Answer

My best hypothesis is that these are common mode noise filters

The thick regions in each section represent capacitors, most likely to the ground plane of the pcb.

The half loop pattern in the middle would seem to be a common mode choke for really high frequency noise. USB 3.0 runs in the gigahertz so this seems about right. The common mode choke is a classic approach to reducing noise common to both sides of a balanced line while having little effect on the differential signal that is desired.

Together these form a CLC filter called a balanced PI filter network.