High Speed ADC

Aug 09, 2007 3 Replies
C

Hi all:


I am trying to reconstruct a periodic exponential signal curve. The signal is in the order of 10-20mV. The total length of this curve is



100ns. Even though the total length is 100ns, the peak bandwidth of the signal maybe in the order of 100MHz. I thought about getting only one data point for each period and delay the sampling instance and collect further points (similar to time-interleaved sampling). I have a programmable delay line, which can produce delays in the multiples of 200ps. The goal is to reconstruct the signal curve, no matter how slow the reconstruction is.

I thought about using high speed ADC like ADS5463 from TI, the reason is that it can handle very high Analog input frequency. Or can I use a slower ADC? The sharpness/jitter of the clock-signal and ADC sample/ hold is very important, I feel. Should I consider anything else?



I dont know how could I interface the ADC to collect the digital data. Does FPGA work? Is there any FPGA boards which can be programmed to handle this situation.



Is there any ideas. I am pretty new to FPGA and ADCs.


Thanks, Joe



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C

You do not need a delay line. Just chose the period of your signal and your sampling frequency appropriately. For example if you sample with a 101ns period you get 1GHz equivalent time sampling because you hit your signal at relative position t, t

+1ns, t+2ns, ...

Kolja Sulimma

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J

The reason for my chosing the delay line was to use the same clock pulse which is used to generate the source (producing the periodic exponential signal).

But I think your suggestion looks good. I can as well use two independent clocks. Is there any place where I can buy two clocks integrated in one package, which start pulsing at the same instant but with slightly different periods (for example, 100ns and 101ns)??

Is there any other considerations to be taken care of?? Any suggestion on ADC or FPGA board selection??

Your help is greatly appreciated.

Thanks, Joe

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C

You do not need to start them at the same instant. You get a periodic image of a periodic signal. If you care about the phase alignment at all you can probably figure it out from the data anyway. If you know the frequency of your signal you can even measure the exact frequency of your sampling crystal from the data.

You can use pretty much any ADC if you add a fast sample and hold circuit in front. But there also are ADCs that have a bandwidth well above their sampling frequency.

Kolja Sulimma

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