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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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