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[FAQ] When implementing a USB 3.x signal redriver, what is the difference between pre-channel loss and post-channel loss?

Other Parts Discussed in Thread: TUSB1002A

I am implementing a USB 3.x signal redriver to help with signal integrity issues. I understand that a redriver provides equalization to the signal path but what losses are affected by this equalization? 

  • In general there are two concepts that need to be taken into account to understand what losses are affected by your USB 3.x signal redriver, Pre-channel loss and Post-channel loss. “Pre-channel” loss refers to any loss that occurs before USB 3.x signal redriver’s receiver. “Post-channel” loss refers to the loss that occurs after the USB 3.x signal redriver’s transmitter.  Trace length and trace width heavily influence the Pre-channel and Post-channel loss. USB 3.x signal redriver equalization function, primarily, takes place at the receiver and compensates for the all the Pre-channel loss and a small portion of the Post-channel loss. Keep in mind that for dual channel devices, like TUSB1002A, the Pre-channel and Post-channel losses are not the same for channel one versus channel two. For Pre-channel and Post-channel length recommendations, please refer to your specific USB Host design guidelines and TI USB 3.x redriver design guidelines.