fuzziness around traces for noisy signals in waveforms analog scope display

[GreenLed]

Hello,

I am trying to interpret the fuzziness around some traces I get sometimes in the scope display. I put some pictures of I2C acquisitions on an AD2.

I am guessing that the Waveforms is trying to display the current block of samples in the bright colors and the previous block of samples  that triggered in a more faded fuzzy color. Is that correct? Is there explanation in the documentation somewhere? I can't find it. This kind of reminds me of a persistence of vision on an analog scope where paler traces are superposed with stronger traces because our eyes can't see that there are several scope sweeps.

 

The problem with that theory is that if I put it in single trigger,  I  get the fuzziness in 10us/div and slower. It is sharp when I am at 5us/div and faster. How does this fuzzy feature supposed to work?

 

Also, is there a control where I can disable/enable the fuzzy feature?

Thanks.

 

Single mode 10 us/div:

Single mode 5 us/div

Continuous mode:

[JRys]

Select the Options (Gear/Cog) and on the menu uncheck Acquire Noise

[JColvin]

There are some additional details about the noise band in this Forum thread here:

Thanks,
JColvin

[attila]

 

[GreenLed]

Hello,

Thanks for all your replies. Unchecking that box does make the acquisition sharper. That helps.

 

After trying the checkbox, I looked in the help at:

file:///C:/Program%20Files%20(x86)/Digilent/WaveForms3/doc/index.html

It says

Noise: check to acquire scope noise samples, uncheck to speed up acquisition rate.

I am trying to figure out what it means to "acquire scope noise samples". I disconnected and reconnected the negative scope input to ground and found some difference. Does the "acquire scope noise samples" have anything to do with some extra averaging computations, or an extra ADC path to sample somewhere in the AD2 some noise at a point in the circuit?

Thanks.

Edited August 17, 2022 by GreenLed

[attila]

Hi @GreenLed

The noise band is useful to indicate glitches, noise, higher frequency components that could be otherwise hidden with averaged samples at lower capture rates.
The acquisition rate impact is due transferring more data, it takes 100us-ms, it only influences when capturing at high rate, above 100 captures / second.