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I'm college student from STT Telkom Bandung, i had final task and i must convert analog signal to digital signal so i can process the signal in DSP. I use FPGA xilinx Virtex 4 that don't have ADC so i must connect the ADC to FPGA by my self. Can i connect ADC to FPGA directly or i must use another interface? I have read some information that we need SPI interface, that is true ? What kind SPI interface that i need ? . or SPI interface is a way to connect ADC to FPGA not an IC or hardware . For additional information I work in 100 KHz frequency so i only need ADC with 200 K sps or more. thank you

best regard

First you must choose the type (unipolar or bipolar) and range of input signal (5V, 10V, +-10V ...).
You must check how many bits you need from ADC (8,10,12,14,16).
Then you can select ADC with suitable interface (parallel or serial).
No matter what type is interface you can connect it directly to FGA, if voltage levels for I/Os of ADC and FPGA are the same (usually 3.3V).
For parallel interface you need as many inputs from FPGA as it's resolution ( + convertion_start, chip_select, read, busy, so on...).
For SPI interface you need about 4-5 inputs only (clock, convertion_start, data_in, data_out, and sometimes - busy).
So parallel interface is easy to implement, it takes a few logic inside FPGA, but it takes too many inputs (for 16 bit ADC - about 20 I/Os).
SPI will use more logic, but only few inputs.
Check producers sites to find appropriate chip you need.

Best regards.

thx

You must use pull up resistor for Dout pin of ADC, because when the ADC is sampling the output is in 3-d state, and when conversion is done output goes low. So you can detect 1->0 state change.