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Visitor jackseiko
Visitor
10,711 Views
Registered: ‎04-22-2009

Differential Signal and LVDS

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Hi,

 

I need to use differential signal on my application, I wonder that is it possible to use differential signal on serial input/output ports on spartan-3e? or should I use another output interface? 

 

does spartan-3e provide LVDS 350 mV. If it does, could you explain how to use it ?

 

thanks in advance 

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1 Solution

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Explorer
Explorer
13,857 Views
Registered: ‎11-07-2008

Re: Differential Signal and LVDS

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Hi,

You can convert probably any single ended signal into a differential ouput signal by using OBUFDS primitive.

Things to keep in mind:

1. The differential ouput signals must exit only to the top level IOB pads.

2. Choose the proper pin polarity in the constraint file when defining the pins.

 

I have attached a PDF file to give more info about LVDS standard. For your application, I believe LVDS_25 standard should be good.

 

Heres an example of converting a single ended standard to a differential ended:

 

OBUFDS #(
      .IOSTANDARD("LVDS_25") // Specify the output I/O standard
   ) OBUFDS_inst (
      .O(ServoDataToSOCp),     // Diff_p output (connect directly to top-level port) (p type differential o/p)
      .OB(ServoDataToSOCn),   // Diff_n output (connect directly to top-level port) (n type differential o/p)
      .I(Servo_Data)      // Buffer input (this is the single ended standard)
   );

 

Please let me know if you need any fiurther info.

 

Shax

7 Replies
Explorer
Explorer
13,858 Views
Registered: ‎11-07-2008

Re: Differential Signal and LVDS

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Hi,

You can convert probably any single ended signal into a differential ouput signal by using OBUFDS primitive.

Things to keep in mind:

1. The differential ouput signals must exit only to the top level IOB pads.

2. Choose the proper pin polarity in the constraint file when defining the pins.

 

I have attached a PDF file to give more info about LVDS standard. For your application, I believe LVDS_25 standard should be good.

 

Heres an example of converting a single ended standard to a differential ended:

 

OBUFDS #(
      .IOSTANDARD("LVDS_25") // Specify the output I/O standard
   ) OBUFDS_inst (
      .O(ServoDataToSOCp),     // Diff_p output (connect directly to top-level port) (p type differential o/p)
      .OB(ServoDataToSOCn),   // Diff_n output (connect directly to top-level port) (n type differential o/p)
      .I(Servo_Data)      // Buffer input (this is the single ended standard)
   );

 

Please let me know if you need any fiurther info.

 

Shax

Visitor jackseiko
Visitor
10,634 Views
Registered: ‎04-22-2009

Re: Differential Signal and LVDS

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thank you so much. it is helpful :)
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Visitor mariasessa
Visitor
8,106 Views
Registered: ‎11-19-2012

Re: Differential Signal and LVDS

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Hi,

 

I want drive a device with a signal LVDS, but I have a problem.

 

With OBUFDS primitive and the configuration i have  VIDIFF=700mV.

 

How I can obtain a VIDIFF=350mV?

 

BR,

Maria

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Historian
Historian
8,087 Views
Registered: ‎02-25-2008

Re: Differential Signal and LVDS

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@mariasessa wrote:

Hi,

 

I want drive a device with a signal LVDS, but I have a problem.

 

With OBUFDS primitive and the configuration i have  VIDIFF=700mV.

 

How I can obtain a VIDIFF=350mV?

 

BR,

Maria


is the signal terminated properly?

----------------------------Yes, I do this for a living.
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Visitor mariasessa
Visitor
8,076 Views
Registered: ‎11-19-2012

Re: Differential Signal and LVDS

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Hi bassman,

I think that the signal is terminated properly.

 

The project is on a Virtex 6, on board ML605.

 

I use OBUFDS primitive with a signal in Input and a pair of PAD nets in output.

The output is configugured on FMC HPC with daughter board (XM105 debug card).

The output is configured on two pin for LVDS signal (pin p and pin n).

The synthesis runs correctly without error.

With a multimeter, I'm measuring the voltage on this pin, and I obtained a VIDFF of  700mv, not 350mV. Why this?

 

With this signal i must driver l'input of a camera on camerallink bus (this bus use a signal LVDS).

Now, i can read the LVDS signal from camera how the clock signal.

I'm working without chip national!

 

BR,

Maria

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Xilinx Employee
Xilinx Employee
8,020 Views
Registered: ‎01-03-2008

Re: Differential Signal and LVDS

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> I think that the signal is terminated properly.

> The output is configugured on FMC HPC with daughter board (XM105 debug card).

 

There are no termination resistors on the FMC-XM105.

------Have you tried typing your question into Google? If not you should before posting.
Too many results? Try adding site:www.xilinx.com
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Historian
Historian
8,014 Views
Registered: ‎02-25-2008

Re: Differential Signal and LVDS

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@mariasessa wrote:

Hi bassman,

I think that the signal is terminated properly.

 

The project is on a Virtex 6, on board ML605.


 

Um, this is the Spartan forum, not the Virtex forum. 

 

And you "think" it's terminated properly? Either it is, or it isn't. Verify whether it is or not.

 

----------------------------Yes, I do this for a living.
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