Xilinx LVDS

Hi,

I want to findout the minimum accepted voltage difference for LVDS in
Xilinx Spartan3 FPGAs. For example is 40mV acceptable?

Many thanks for the help in advance..

H aka N

Hi, I think it is, as you can see from table 21 on page 23 of DS099-3
(Spartan3 datasheet), LVDS low input is (Vicm - 0.125), while LVDS high
is (Vicm + 0.125), so the difference is 25mV.
Marco

<hakan.sakman@gmail.com> wrote in message 
news:1141729977.923850.43780@e56g2000cwe.googlegroups.com...
> Hi,
>
> I want to findout the minimum accepted voltage difference for LVDS in
> Xilinx Spartan3 FPGAs. For example is 40mV acceptable?
>
> Many thanks for the help in advance..
>
> H aka N
>
Did you try looking in the datasheet? Search for Vid.
HTH, Syms. 

Sorry for the mistake, it's 250mV!

"Marco" <marco@marylon.com> wrote in message 
news:1141730919.700121.50560@v46g2000cwv.googlegroups.com...
> Hi, I think it is, as you can see from table 21 on page 23 of DS099-3
> (Spartan3 datasheet), LVDS low input is (Vicm - 0.125), while LVDS high
> is (Vicm + 0.125), so the difference is 25mV.
> Marco
>
Marco,
You might want to read that again. You're reading the table headed 'Test 
Methods for Timing Measurement at I/Os'. Perhaps the table 'Recommended 
Operating Conditions for User I/Os Using Differential Signal Standards' 
might be more applicable? And also, I suggest a little more practice at 
arithmetic. Or typing. 250mV is what you were looking for? ;-)
HTH, Syms. 

Thanks all for your time,

I looked at the data sheet (didn't know where to look at, a search on
LVDS didn't help, so many tanks for the directions) and as far as I can
see its min 100mV and max 600mV..

Best

H aka N

Marco wrote:

>Hi, I think it is, as you can see from table 21 on page 23 of DS099-3
>(Spartan3 datasheet), LVDS low input is (Vicm - 0.125), while LVDS high
>is (Vicm + 0.125), so the difference is 25mV.
>Marco
>
>  
>
Funny, I read what you have above as 250 mV.
40 mV should work, at the chip, but leaves very little room for external 
noise
sources.  A very short run might work fine, but a long cable between 
separate
pieces of equipment could easily pick up enough noise that is not perfectly
balanced and cause errors.

Jon