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USB Superspeed Peripherals

Anonymous
Not applicable

Hello,

   

I am designing a FX3 board with Spartan 6 FPGA.

   

My question is: "Do I need 22 Ohm termination resistors on GPIF 2 interface".

   

I couldn't make a signal integrity simulation since there is no ibis model of the FX3 chip.

   

The PCB will be very small. FX3 and Spartan 6 will be very close to each other.

   

Nearly all GPIF pins will be connected to the FPGA.

   

 

   

Regards,

   

Ersin OEZALP

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1 Solution
AliAsgar
Moderator
Moderator

Hi,

22-Ω series resistors are recommended to avoid the reflection phenomenon, impedance mismatch on the GPIF lines and also due to PCB stack up. Hence, we recommend using 22-Ω series termination resistors to avoid reflection on these lines.

Best Regards,
AliAsgar

View solution in original post

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3 Replies
LiMa_282146
New Contributor II

Hi,

   

There is an ibis model for the FX3. Maybe you need to raise a support case with Cypress to get it.

   

Sodafarl

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SeAn_4634356
New Contributor

Hi Ersin,

I have absolutely the same question

Should I put GPIF2 22 ohm termination resistors if source IC and FX3 are close to each other?

FX3 acting as signal/clock receiver.

To be more specific, in my particular case:

  • Max sourceIC to FX3 GPIF2 wire length is 28.39mm
  • Min sourceIC to FX3 GPIF2 wire length is 18.37mm
  • Length mismatch 10.02mm
  • Source IC clock frequency 74.25 MHz
  • Source IC signal rise / fall time = 1ns

I found some guide from Analog Devices https://www.analog.com/media/cn/training-seminars/tutorials/MT-097.pdf

Acording to this guide termination resistors advised if microstrip length is greather than 2 inches * t(rise or fall), ns

I guess no resistors needed for my case because max wire length without termination resistors is 51mm.

What would the Cypress FX3 engineers advise?

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AliAsgar
Moderator
Moderator

Hi,

22-Ω series resistors are recommended to avoid the reflection phenomenon, impedance mismatch on the GPIF lines and also due to PCB stack up. Hence, we recommend using 22-Ω series termination resistors to avoid reflection on these lines.

Best Regards,
AliAsgar

View solution in original post

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