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Oscilloscope input noise comparison
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srce:

--- Quote from: nctnico on November 12, 2018, 01:09:00 pm ---
--- Quote from: JPortici on November 12, 2018, 12:42:40 pm ---is it me or is the 20 MHz trace for the keysight showing a digital filter?

--- End quote ---
Well spotted and I agree that it looks like a simple digital filter.  y[n]= (y[n-1] * (a-1) + x[n]) / a.

--- End quote ---

You can choose between 20MHz or 200MHz h/w filter or s/w with any bandwidth. That was indeed with s/w filter.

One other point to bear in mind is that the scope h/w does actually have >8GHz of b/w. Mine is just s/w limited to 2GHz.
2N3055:
Keysight MSOX3104T (1GHz 5/GSa/sec) and Picoscope 3406D (200MHz 1/GSa/sec)

50 Ohm terminator on input.

https://drive.google.com/open?id=1kZEO_hKSXGY_-ScaOQO3ydRLsjV2okpD

Regards,
Sinisa
maxwell3e10:
It looks like the noise on 50 Ohm setting and 1 MOhm setting is identical for Keysight MSOX3104T. Just want to make sure its not a mix-up of files.
maxwell3e10:

--- Quote from: srce on November 13, 2018, 04:54:53 pm ---One other point to bear in mind is that the scope h/w does actually have >8GHz of b/w. Mine is just s/w limited to 2GHz.

--- End quote ---

This brings an interesting general point with the recent trend of software-upgradable scopes. When a scope is software limited in the maximum sampling rate and bandwidth, does it typically run the ADC at the maximum rate and then averages samples? Does it have a switchable analog front-end  filter?  It needs some type of anti-aliasing filter, both for noise purposes and to avoid signal aliasing.
2N3055:
I checked, Std Dev on those files shows lower RMS noise on 50 Ohm.  Cca. 326uV RMS vs 343uV for 1GHz bandwidth (50 \$\Omega\$ vs 1M) and 112uV vs 176uV for 20MHz bandlimited. I believe they should be right.
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