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Design >> High-Speed I/O Design >> USB High Speed Eye Pattern with Switch
https://designers-guide.org/forum/YaBB.pl?num=1174557712

Message started by fonseca.ha on Mar 22^nd, 2007, 3:01am

Title: USB High Speed Eye Pattern with Switch
Post by fonseca.ha on Mar 22^nd, 2007, 3:01am

Hi
I am designing a USB 2.0 PHY and a costumer requested, the insertion of an analog switch such as FSUSB30 in the PCB board. Does any of you have experience on how such a switch will impact the HS TX Eye pattern? What PCB layout considerations should be made?

Thank you,
H.

Title: Re: USB High Speed Eye Pattern with Switch
Post by SRF Tech on Apr 12^th, 2007, 8:58am

It a matter of a few factors:

1. Insertion loss: How much will the insertion loss attributed to this switch attenuate your transmitted signal? Remember insertion loss is very frequency dependent, so it may also distort your EYE diagram.

2. Reflections: If the switch and the PCB layout does not properly account for matching impedances for your signal traces, then you may introduce many unwanted reflections. not only can this reduce your EYE but it can dramatically impact your Inter-symbol interference, and subsequently your Bit Error Rate.

Final answer: To ensure the switch has a minimal impact to your EYE diagram, make sure it looks like a transmission line by all respects, matched to the impedance of your signal trace.