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Visitor drinu8
Visitor
5,831 Views
Registered: ‎10-21-2015

Artix 7 XC7A200TIBUFDS output impedance

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Hi,

 

I am designing a PCB board to be used with another board to send high speed data from the FPGA to a DAC. Now the FPGA is already routed on its board, on which the tracks have been matched single ended to 45Ohms. As I will be using LVDS, I matched my tracks (on another board which will be connected to the FPGA board) with a differential impedance of 120Ohms (DAC diff. input impedance is 120Ohms). Thus some reflections will surely be present (which I obvioudly want to minimize). To obtain a rough value for the magnitude of these reflections, I wanted to run some simulations for which I require the output impedance of the IBUFDS buffer at the pin of the FPGA (to check matching from output of FPGA to track). Anyone knows were I can find this, or should I assume that this is matched to a diff. 80-100Ohms impedance? [As Xilinx suggests - UG586, a differential impedance of 80-100Ohms]. I already searched through the docs - Artix 7 DataSheet DC and AC Switching Characteristics and Artix 7 Series SelectIO but had no success.

 

Other Info - Total length of a typical differential track (in my case) is more than 9cm and less than 13cm.

 

Any suggestions/comments?

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Explorer
Explorer
10,560 Views
Registered: ‎10-14-2015

Re: Artix 7 XC7A200TIBUFDS output impedance

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Hi Drinu8,

 

Please refer page 90 for LVDS interface for 7 Series:

http://www.xilinx.com/support/documentation/user_guides/ug471_7Series_SelectIO.pdf

LVDS is typically used to route data and clocks between boards.Since the transition times of LVDS signals are typically 500 ps, all circuit traces over 80 ps (1/6 of 500 ps) in electrical length must be treated as transmission lines. Assuming an FR4 PCB (printed-circuit board) transmission line has a propagation delay of 165 ps/inch, a 1/2-inch trace must be considered a transmission line when transmitting LVDS.

 

Again it depends on the stackup and impedence of the design ,It is recommended to use 100ohm termination for standard LVDS.

 

Please refer different routing guidelines for The LVDS I/O Standard in below link:

http://www.xilinx.com/support/documentation/application_notes/xapp230.pdf

 

 

Thanks,
Sarada

 

 

Kindly note- Please mark the Answer as "Accept as solution" if information provided is helpful.

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Xilinx Employee
Xilinx Employee
5,667 Views
Registered: ‎08-01-2012

Re: Artix 7 XC7A200TIBUFDS output impedance

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You can download Artix-7 IBIS models from the below link

http://www.xilinx.com/support/download/index.html/content/xilinx/en/downloadNav/device-models/ibis-models/artix-series-fpgas.html

 

FYI: Signal Integrity (SI) resources & documentation can be found in below links

http://www.xilinx.com/products/technology/signal-integrity.html  

http://www.xilinx.com/products/design_resources/signal_integrity/resource/resources.htm

________________________________________________

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Explorer
Explorer
10,561 Views
Registered: ‎10-14-2015

Re: Artix 7 XC7A200TIBUFDS output impedance

Jump to solution

Hi Drinu8,

 

Please refer page 90 for LVDS interface for 7 Series:

http://www.xilinx.com/support/documentation/user_guides/ug471_7Series_SelectIO.pdf

LVDS is typically used to route data and clocks between boards.Since the transition times of LVDS signals are typically 500 ps, all circuit traces over 80 ps (1/6 of 500 ps) in electrical length must be treated as transmission lines. Assuming an FR4 PCB (printed-circuit board) transmission line has a propagation delay of 165 ps/inch, a 1/2-inch trace must be considered a transmission line when transmitting LVDS.

 

Again it depends on the stackup and impedence of the design ,It is recommended to use 100ohm termination for standard LVDS.

 

Please refer different routing guidelines for The LVDS I/O Standard in below link:

http://www.xilinx.com/support/documentation/application_notes/xapp230.pdf

 

 

Thanks,
Sarada

 

 

Kindly note- Please mark the Answer as "Accept as solution" if information provided is helpful.

Give Kudos to a post which you think is helpful and reply oriented.

 

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