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| Oscilloscope input noise comparison |
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| Performa01:
--- Quote from: _Wim_ on December 23, 2018, 10:15:04 pm ---I agree this is related to the trickery, but do not understand why the 12bit mode is worse, because that sample rate is supported directly by the ADC without trickery (unless the ADC does some internal trickery off course). --- End quote --- It could be different signal paths for clock and input signals (even on the chip) with slightly more crosstalk in 12-bit mode? -110 dBu isn't a very high level after all (<2.5µVrms or <7µVpp). In the +/-10mV range, this is equivalent to some -80dBFS. PicoTech specifies only 60dB SFDR (but that is irrelevant without a signal) and 110µVrms noise in 12-bit mode. So there is no specification for spurs without a signal, but I guess the -80dBFS is simply the performance limit of a 5000 series PicoScope. |
| thanasisk:
Would be very very interesting to plot the low frequency input noise density of the scopes, i.e. dc to 500 kHz. Is this possible already with the same measurement files? |
| Performa01:
--- Quote from: thanasisk on December 23, 2018, 10:52:54 pm ---Would be very very interesting to plot the low frequency input noise density of the scopes, i.e. dc to 500 kHz. Is this possible already with the same measurement files? --- End quote --- No it isn't. We need limit the record length - hence the sample rate - or the files would get huge. Because of the the split-path design of the input buffer (and the FET amplifiers required for this), the noise in the DC/LF path is very high. So the noise plot below some 10kHz will most likely be ugly for just about any reasonably modern standard scope. |
| nctnico:
--- Quote from: Performa01 on December 23, 2018, 11:09:40 pm --- --- Quote from: thanasisk on December 23, 2018, 10:52:54 pm ---Would be very very interesting to plot the low frequency input noise density of the scopes, i.e. dc to 500 kHz. Is this possible already with the same measurement files? --- End quote --- No it isn't. We need limit the record length - hence the sample rate - or the files would get huge. Because of the the split-path design of the input buffer (and the FET amplifiers required for this), the noise in the DC/LF path is very high. So the noise plot below some 10kHz will most likely be ugly for just about any reasonably modern standard scope. --- End quote --- But this would need to be measured with the bandwidth limit on and the samplerate needs to be 100Ms/s or more otherwise the HF noise will alias into the lower frequencies. |
| egonotto:
Hello, I have on my 5243A and 5444B strong spur at 31.25 MHz. Best regards egonotto |
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