| Products > Test Equipment |
| How much noise floor and other things matter in oscilloscope usability |
| << < (5/63) > >> |
| 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. |
| Navigation |
| Message Index |
| Next page |
| Previous page |