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Altera_Forum
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16 years ago

Using differental input buffer as comparator

Hi, I'm designing a system using comparators to signalize analog signals, I wanna know that can I use the differental input pins on FPGA as comparators? If it is possible, the PCB will be smaller ...
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Altera_Forum
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16 years ago

I suppose you could if the conditions were right. You would be restricted to the limitations of the device as far as the voltage levels.

Look at the datasheet for the device you intend to use. For example, here is the datasheet for Stratix IV:

http://www.altera.com/literature/hb/stratix-iv/stx4_5v4_01.pdf

Page 1-10 gives the differential IO standards specifications. So for example, if you look at LVDS, the minimum Vid (differential input voltage) is 10mV. Anything less than that and it would not be able to "compare". Also note that you must obey the Vcm (common mode voltage) of the device. This is where I think the usefulness as a comparator breaks down.

Jake