Analog Discover 2 Noise Floor at Different Attenuation Levels in Spectrum Analyzer

[JohnC124]

Hello,

I'm trying to use the analog discovery 2 and the waveforms spectrum analyzer mode to take some noise spectral density measurements. Something I noticed is that the noise floor of the analyzer does not change when I changed the channel attenuation from 1X to 0.1X. I would have expected the noise floor to decrease by 10X since an attenuation of 0.1X would imply a gain of 10 in front of the AD2. Going to 0.01X does decrease the noise floor by a factor of 10 (compared to 0.1X) but it should be a factor of 100 lower than the noise floor in the 1X case. Setting the attenuation to 10X or 100X increases the noise floor by a factor of 10 each time as I would expect. 

Long story short: are the 0.1X and 0.01X attenuation settings in the spectrum analyzer implemented correctly in software? They do not change the noise floor of the analyzer as I would expect. 

Thanks for any help you can provide, I can also attach screen shots if necessary to show the behavior more clearly. 

[attila]

Hi @JohnC124

The AD2 has two input ranges (gains), with 1X 50/5Vpk2pk, 0.1X 5/0.5V, with 0.01X 0.5/0.05V, with 10X 500/50V...
With 1X and 5V range the scope input is in low range but with 0.1X and 5V in high range, so the resolution will be about the same. See the Trace info on bottom left of your plot area.
To have the same input range/gain after changing the attenuation adjust the range option to the lower or higher value.

Edited September 6, 2022 by attila

[JohnC124]

Awesome, that gave the expected behavior, thank you!