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Old 12-03-2007, 01:50 PM
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Default Re: Interfacing Cyclone III to 3.3v LVDS devices

>> How can i interface the cyclone III with 2.5v LVDS to 3.3v LVDS adc &
>> dac ?

>
>If you set 3.3v to a i/o block and Quartus does not allow you to
>assign LVDS on a pin of that block (w/ an error message when fitting)
>tell quartus you have 2.5v (despite you will use 3.3v in your board)
>It will pass compilation and will work great.
>I had that issue on CycloneII driving clocks to ADCs from Analog
>devices, I'll bet will be the same on CyIII.


For LVDS transmission from 3.3V I/O, if all three matching resistors
(at the transmitting end) are 150 ohm then this gives output levels to
the LVDS specification and presents 100 ohm to the line. The only
disadvantage (compared to 2.5V operation) is an increase in power
dissipation.
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