How to measure frequency stability (jitter)

[JC Gauthier]

Hi,

I am trying to measure the frequency stability of an optical chopper over time using the Digilent Discovery 2. When using the Scope tool, I can see the square pulse train generated by the chopper, and the Frequency measurement gives me the frequency value I am expecting. 

However, I would like to record the frequency values over time for statistical analysis. Unfortunately, the logging option in the Scope tool only allows me to save (for instance) the current value, average or min/max values over the acquisition time, but not the set of recorded values itself. The Logger tool also does not seem to be able to record frequency values from my understanding. 

Is there a way to access or record the values given by the frequency measurement for a set number of acquisitions? This would save time compared to saving a long pulse train and writing an external code to evaluate the frequency jitter on the signal.

Best,
Jean-Christophe  

[attila]

Hi @JC Gauthier

You can use Logging Script for logging or Measurements to performs statistics.

A more accurate measurement way would be using oscilloscope and FFT/Spectrum analyzer with averaging or peak hold.

FileAppendLine("~/Desktop/scope/measure.csv", [(new Date()).toISOString(), Logic.Channels.DIN0.measure("Frequency")])

[JC Gauthier]

Great! It worked :)

I just had to change DIN by DIO on my version. 

Just to know, is there a way to select the sampling rate of the measurement acquisition? 

Best,
JC

[attila]

Hi @JC Gauthier

The capture sample Rate can be adjusted in the top right.
For Digital Discovery the input mode can be selected 100-200MHz/32bit, 400MHz/16bit or 800MHz/8bit