EEVblog #601 - Why Digital Oscilloscopes Appear Noisy
Why Electrical Engineering Stack Exchange recommends it
Electronics Stack Exchange answerers and commenters point people to it when explaining that a scope's displayed noise is real signal noise shaped by bandwidth, memory depth and resolution, not a flaw of digital scopes.
Recommended by 2 people across 3 different months, 2017 to 2020.
What it is
Dave Jones of EEVblog explains why digital oscilloscopes often look noisier than analog ones and argues that this is largely a myth. He demonstrates on a Tektronix MDO3000, Rigol DS1052E, Tektronix TDS220 and an analog Tektronix 2225, showing how memory depth, bandwidth, averaging and intensity-graded displays change what you see.
What people said
Recommends Bimpelrekkie · 2017-09 · Electrical Engineering Stack Exchange · on “Analog scope has infinite resolution (vertical)?”
Next time a "dude" tells you something, ask them to **elaborate** on that. That usually shuts up these "dudes" as it is often just **their own misconception** of how things work. So say: **OK, now prove it**. I can prove the "Dude" is **WRONG** and so can you after watching Dave from EEVBlog explaining how things do work: [this video] Sure the video is about noise but that is what limits the resolution so it still applies.
Recommends Bimpelrekkie · 2017-12 · Electrical Engineering Stack Exchange · on “Measuring noise with an oscilloscope”
Do you **see** the noise increasing/decreasing if you **short** the noisy resistor ? If not: you're not measuring the resistors's noise. Maybe this video will also help: [this video] In my opinion you would need to **amplify** the noise (using a low noise amplifier with a known gain and BW) before you can properly measure the noise on a scope. A scope's input impedance is 1 Mohm and not designed for low noise. You would need a scope with 50 ohm inputs. If available: use a spectrum analyzer.
Recommends vofa · 2020-11 · Electrical Engineering Stack Exchange · on “Oscilloscope "noise"?”
Look at it this way: [LINK] All signals in reality have noise. The oscilloscope samples a signal, with its inherent noise, and converts it to a digital number that has a minimum resolution. It rounds values to their nearest discrete digital representation. The green lines are spaced at the scope's sample rate. The red line is a central value, with ± 1 bit of noise. This is normal--there is always noise in the signal you're measuring and in the conversion process. The sequence of digital numbers is eventually turned into an image, and that process can exaggerate this small noise depending on how the waveform is scaled and positioned. Your square wave looks about as good as as square ever look
Cites Paul Uszak · 2017-02 · Electrical Engineering Stack Exchange · on “Is measuring noise as V/√Hz obsolete?”
Having reviewed answers I'm convinced that actually, they're the same thing just expressed differently. I'm not certain of watts /Hz, but certainly for simple amplitude of a noise signal there is no significant difference between V/√Hz and a μ, σ statistical representation. They're just two sides of the same coin. The winning evidence came from EEVblog Dave's noisy digital oscilloscope explanation [this video] . Look around 6 min 50s. Noise drops as memory depth drops. This is what you expect statistically and what I've found with my Rigol. He used a Tek 3000 series model costing considerably more. Bandwidth on a DSO is actually closely related to sample rate through Shannon's sampling theory. Th