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Adventurer
Adventurer
187 Views
Registered: ‎01-26-2017

A7 FPGA GTP's signal AC couple solution

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I have a new project for high speed communication between 2 FPGAs. I connect these 2 FPGAs with GTP. The additional requirement is the cable btween the GTP should be least 5 meters long, so that a redriver chip is need for signal enhancement. 

It is request to do AC couple on GTP's RX port through the long cable, which means the GTP will receive the signals in AC wave. Can GTP receive and correctly recognize the AC mode signals? It seems the FPGA should have bulid-in bias circuit for it.

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Moderator
Moderator
158 Views
Registered: ‎07-30-2007

Re: A7 FPGA GTP's signal AC couple solution

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Ac coupling with a 100nf cap is the normal connection for GT's.  See UG482 page 235.




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Moderator
Moderator
159 Views
Registered: ‎07-30-2007

Re: A7 FPGA GTP's signal AC couple solution

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Ac coupling with a 100nf cap is the normal connection for GT's.  See UG482 page 235.




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Adventurer
Adventurer
146 Views
Registered: ‎01-26-2017

Re: A7 FPGA GTP's signal AC couple solution

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On page 114 of UG482, Fig 3-21 shows these are pre-drivers in GTP transceiver. I am not sure if the pre-driver can improve the SI when I connect GTP with 5m length cable.

 

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Moderator
Moderator
133 Views
Registered: ‎07-30-2007

Re: A7 FPGA GTP's signal AC couple solution

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The predrivers are just part of the GT channel.  The main thing is whether you have enough preemphasis to drive 5 meters.  I would suggest using the IBIS-AMI models to simulate this situation and see if it is viable or possibly trying this with one of the development boards.




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Teacher drjohnsmith
Teacher
62 Views
Registered: ‎07-09-2009

Re: A7 FPGA GTP's signal AC couple solution

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From experiance, Id strongly recomend including driver / receiver chips outside the fpga if your driving cables,

blowing a driver with ESD or shorted signals is a pain, blowing a FPGA can give you a real bad day.
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