# High-Speed Digitizers

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## How to calculate the noise level of a digitizer given sampling rate

Hi, I'm working with the Digitizer PXIe5160 and our goal is to capture a 100MHz signal sampled @250MS/s. However, our application is very sensitive to noise and we'd like to know how to measure the noise level of the digitizer given the fact that I'm not using the full bandwidth of the system.

I appreciate your kind help on this matter.

Cheers

Jorge Gomez

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## Re: How to calculate the noise level of a digitizer given sampling rate

Noise (peak to peak) is a function of bandwidth, so if you reduce your bandwidth you will measure lower noise.

What information do you want to measure? (amplitude, phase/frequency)

A pure sine or some modulation? How fast change these properties (results in a bandwidth).

If you have your 5160 configured for the measurement, just terminate the input (50 ohm , or whatever your source is).

Now do some measurements and look at the noise/distribution of your result.

If you have a model of your source (signal) you can fit that to your data and/or Lock-in for periodical signals.

Greetings from Germany
Henrik

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## Re: How to calculate the noise level of a digitizer given sampling rate

Hi Henrik, thanks for your email. My goal is to compute the signal to noise ratio from an OFDM signal captured from the PXIe5160 digitizer. So, my first step is to calculate the noise power that the PXIe5160 gives me and then compute the power of my OFDM signal.

Just to see if I understood correctly, you're suggesting to terminate the port of the digitizer with a 50-ohm load and then do a sample capture? If so, do you suggest to have the minimum amplitude scale for the digitizer?

Cheers

Jorge Gomez

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