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How much noise floor and other things matter in oscilloscope usability
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David Hess:
Noise level almost never matters because oscilloscopes are time domain instruments with two more significant limitations:

1. Noise is typically lower than the aberrations in the pulse response, and this is also a limit for instruments with resolution higher than 8 bits, so removing the noise just gives a clearer view of an inaccurate result where it counts.

2. Input stage offset and drift is usually greater than the noise.

And unlike the above errors, a digital storage oscilloscope can reduce noise with averaging.

Where noise does matter is spectrum analysis, but again, other limits like distortion have a greater effect.  Optimizing oscilloscope input stages for pulse response requires compromise in noise and distortion.

Good low noise performance for a 100 MHz instrument should be about 40 microvolts RMS based on a input JFET source follower with 3.2 nV/Sqrt(Hz) noise, and many old analog oscilloscopes and DSOs achieve this.  This is also why sensitivity below a couple millivolts/division is questionable except if bandwidth is limited.

For instance my 2232 DSO has 25 points per division so at 2 millivolts/division each point is 80 microvolts, and peak-to-peak noise is 3 points or 240 microvolts which comes out to 40 microvolts RMS.  I measured slight lower than this on some of my analog oscilloscopes under similar conditions, although my favorite analog oscilloscope has a noise level about 3 times higher than this.
Fiorenzo:
So, with these settings:
1x probe, no BW limit, normal acquisition mode

I did other photos:
1) probe grounded to its tip
2) probe connected to a Power supply to check the ripple
3) no probe attached to the oscilloscope

What do you think about the noise floor?
It seem high to me....
Fiorenzo:
Here same settings but hi-res mode.

bdunham7:
Can you try again only set the vertical scale to 1mV/div and measure with no probe and with the shorted probe?  Then do the same at 100mV/div.
Fungus:

--- Quote from: Fiorenzo on December 24, 2021, 06:15:24 am ---So, with these settings:
1x probe, no BW limit

--- End quote ---

Again: You're not supposed to use 1x with no BW limit. Ever.

1x with no BW limit = noise.


--- Quote from: Fiorenzo on December 24, 2021, 06:15:24 am ---2) probe connected to a Power supply to check the ripple

--- End quote ---

You can see the ripple, right? That's what counts.

Try the same thing with the bandwidth limiter on.
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