xilinx - Can I use differential I/O pins of FPGA as high speed comparator?

High speed comparators are rather expensive and speed is what FPGAs are very good at. On the other hand, FPGAs (in my case: XC3S400) have paired differential pins in each bank that their voltages are compared ( At least I think so !). They also have Vref for single ended standards that may act as a comparator.

I want to know if I can use those differential I/O pair pins as a comparator -and if so- how should I do that ( Should I connect a vref and use single ended standards or simply connect two voltages to differential I/O pins ?)

EDITION: I tried it and works excellent !!!

Answer

Yes you can. There are some applications notes using the differential pairs inside an FPGA as a low cost ADC.

There is a very good document describing this that you can use for your design:

Analysis on Digital Implementation of Sigma-Delta ADC with Passive Analog Components