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USB Superspeed Peripherals

GiAn_4200716
New Contributor

Hi all,

I'm designing a FPGA board that uses FX3 IC to communicate through USB type-C connection to PC.

I read through the forum and I've examined the gerbers for DVK and SuperSpeed Explorer Kit and I saw that the GPIF bus lines are routed with single-ended impedance of 50 ohm.

My questions are:

is the 50 ohm impedance requirement mandatory (and, eventually, why?) This requirement is to be met in addition or alternatively to length-matchng of those traces?

The center-to-center distance between FPGA and FX3 is < 900 mils, hardly the length of traces could be < 500-600mils .

So I quickly estimated the bandwidth for a 50% duty-cycle 100 MHz square wave to about 1GHz (~98% of the power), so 1/10 of the relative wavelength (and, consequently, the maximum conductor length) is ~1200mils (~3 cm).

As I said, this is a rough estimation,but is reasonable that <1500mils long traces (matched as closely as possible) could work out well?

I ask this as I could not do signal integrity analysis with my tools.

Thanks in advance for your replies.

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1 Solution
Hemanth
Moderator
Moderator

Hi,

what is mandatory is length-matching the traces within the trace length of 500mils. As you said and as a thumb rule 50 Ohm impedance matching is required when the tracelength exceeds one-tenth of the wavelength. But it is good to have impedance matching on the GPIF lines.

Moreover, if the trace lengths as per your calculations exceeds 1200 mils, then it will be mandatory to have impedance matching.

Regards,

Hemanth

Hemanth

View solution in original post

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2 Replies
Hemanth
Moderator
Moderator

Hi,

what is mandatory is length-matching the traces within the trace length of 500mils. As you said and as a thumb rule 50 Ohm impedance matching is required when the tracelength exceeds one-tenth of the wavelength. But it is good to have impedance matching on the GPIF lines.

Moreover, if the trace lengths as per your calculations exceeds 1200 mils, then it will be mandatory to have impedance matching.

Regards,

Hemanth

Hemanth

View solution in original post

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GiAn_4200716
New Contributor

Hi Hemanth,
sorry for late reply.

Thanks for your answer!

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