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morantk
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Registered: ‎09-05-2013

Kintex 7 Output Drive Strength definition

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Hello Xilinx developers,

 

I am looking for some resourses or explantion as to what the Output Drive Strength Attributes do. I see for a given I/O standard you can change the drive strength in mA, for example we are interested in LVCMOS33, which has drive strength options of 4,8,12 or 16. 

 

So I am wondering what the net effect of a change is, and I wondering why you would choose one drive strength over another. Is there an app note for this? 

 

I would be interested in seeing some output curves of the effect of different drive strengths on the output curves.

 

Thank you for you help!

 

Regards

 

Karl

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austin
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Registered: ‎02-27-2008

Karl,,

 

Drive strength determines the output impedance of the driver.  When you do a signal integrity analysis of your board, before you get it fabricated, using the layout and the IBIS models, you then get to see if it will work as designed.


Too weak, and you may not meet timing.  Too strong, and you may have simulaneous swicthing noise, over shoot, under shoot,  ringing, excessive jitter, and data errors (or worse).

 

For example 6 mA or 8 mA is a very good match for pcb 50 ohm impedance controlled traces.

 

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

Austin Lesea
Principal Engineer
Xilinx San Jose

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austin
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Scholar
24,873 Views
Registered: ‎02-27-2008

Karl,,

 

Drive strength determines the output impedance of the driver.  When you do a signal integrity analysis of your board, before you get it fabricated, using the layout and the IBIS models, you then get to see if it will work as designed.


Too weak, and you may not meet timing.  Too strong, and you may have simulaneous swicthing noise, over shoot, under shoot,  ringing, excessive jitter, and data errors (or worse).

 

For example 6 mA or 8 mA is a very good match for pcb 50 ohm impedance controlled traces.

 

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

Austin Lesea
Principal Engineer
Xilinx San Jose

View solution in original post

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morantk
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Registered: ‎09-05-2013

Thanks Austin

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