ADC and FPGA interface

[Altera_Forum]

Dear All 

I am a university student. I have to connect an ADC to my DE2-115 Altera development board.  First problem is, finding a proper ADC for my research but my Analog signal is a kind of special. Low frequency and very low duty cycle as frequency is 10 Hz and only 40 to 200 ns duty cycle (means 100 ms pulse with only 40 to 200 ns duty cycle). Therefore I need a fast ADC to could catch this narrow duty cycle. In the other hand, ADCs with high sampling rate do not work with low frequencies like as 10 Hz!  Can you help me and give me an idea to solve this problem!  2nd problem: I have bought a DEV-ADC34j22 module without notice that it is designed for Cyclone V GT and now I have DE2-115 Altera! I am hoping for some modification like as pin assignment for its HSMC to use it for DE2-115 board! Is it possible! Can you suggest me some alternative ADC for mentioned converting !  Thank you.

[Altera_Forum]

Hi, 

 the first question that comes to my mind: do you really need an ADC? If you want to measure the timing of those pulses, a fast comparator will do (e.g. LT1711).  Okay, maybe you need to detect the pulse and measure it's levels. Then, of course, you'll need an ADC. I just searched Mouser for ADCs with 500 MSa/s (I assume that's plenty for your application with 40ns pulses), and the first one I clicked (ISLA118P50) supports DC-coupling, hence arbitrarily low frequencies. Same for ADC08D500. You'll need a differential input amplifier, though, but that's not a big deal, and a common requirement for high-bandwidth DACs and ADCs. If 100..200MSa/s are sufficient, many ADCs can directly sample a DC-coupled signal.  No idea about your 2nd question, though, sorry.   Best regards, GooGooCluster

[Altera_Forum]

Hi GooGooCluster! 

 Your instructions are highly valuable and useful. Comparators can work for my case. I will try to study and use them. Hope you would be available for some coming questions.   Thank you