how to connect analog input directly to FPGA Altera board?

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my supervisor asked me to implement Sigma Delta ADC on "Cyclone II DE1" board;

now i want to make sure that does circuit mentioned in latticesemi proper for this goal; if i use an analog comparator off chip with RC network; and design other parts of Sigma Delta ADC on FPGA ?

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Yes, you can implement the circuit as shown in the Lattice application note. You could use an external comparator or an external LVDS receiver. An external comparator is better, as it will have a wider input voltage tolerance. Regardless of how you perform your 1-bit A-to-D conversion, you need to make sure you restrict the analog signal swing to whatever the receiver can handle.

Cheers,

Dave