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Oscilloscope input noise comparison
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_Wim_:

--- Quote from: ADT123 on December 29, 2018, 07:26:06 am ---_Wim_ the crystal oscillator in the higher end model is simply a more expensive one that is calibrated at final test.  Other than the accuracy of frequency measurements there should be no other differences.  Other specs such as jitter are the same.

--- End quote ---

Thanks for this info, if it is only about absolute frequency accuracy, that less of interest to me.
maxwell3e10:
I got a more recent model of Owon XDS3062A scope (due to a sale at Arrow.com). The input noise spectrum of it looks somewhat better than an earlier version of the same scope. White noise level is quite low at about 3.5 nV/sqrt(Hz). The rms noise is 46 uV and it remains the same up to full scale of 100mV, thanks to 12 bit ADC. But there is significant 1/f noise and a number of prominent noise  peaks, in particular one near 1.3 MHz. 

The scope also came with a built-in function generator and it has a basic frequency response analysis function (gain and phase) that seems to work OK. The function generator has the same clock as the scope, which can also have some advantages. Not bad for less than $200!

srce:

--- Quote from: srce on November 02, 2018, 10:46:55 am ---Here are some results for a Keysight MSOS204A.

Vertical: 1mV/div - 8 divisions - 10bit
Horizontal: 5uS/div - 20GSa/s - 1Mpts

Yellow is 20MHz B/W (s/w filter) - 50 Ohm - 44uV AC RMS - 350uVpp
Blue is 2.1GHz B/W - 50 Ohm - 115uV AC RMS - 1.1mVpp
50 Ohm terminators on BNC inputs.

2GHz data 50 Ohm

20MHz data 50 Ohm

--- End quote ---

And here's another one with the same settings:

8.4GHz - 50 Ohm - 248uV AC RMS - 2.4mVpp

8.4GHz data 50 Ohm


Nanoman:

--- Quote ---The Picoscope details I have seen show an integrated CMOS transimpedance buffer intended for DSOs from TI that by itself has 100 times the noise of a discrete front end at low frequencies.  I mean literally 1000nV/SqrtHz where a discrete design could be 10nV/SqrtHz.

So a broadband RMS noise of 125.7uV over 200MHz does not surprise me at all and that is about 5 times worse than my 40+ year old 200MHz analog oscilloscopes.

--- End quote ---

3000/5000 series ADA4817-1 (4nV), recent series of scopes. Obsolete versions (early 2000's) employed discrete jfet front ends.
2000 series          ADA4891-1 (9nV) or AD8065 (7nv) (25MHz versions)
4000 series          ADA4891-1 (8 channel scope) and AD8065 on older 20MHz scopes and 4817 on 16bit scope
6000 series          BF998 mosfet (~6nV, obsolete device), 6404 is ~12nv due to attenuator configuration

Either Analog Devices parts or discrete jfet/mosfets. The ADA4891 measures closer to 12nV due to 1/f contribution.

I used to design scopes at Pico and wanted to clear up this misinformation, noise is a critical scope spec and we'd use the best parts whenever possible.
ILIJA:
Hi
Can you share script you used  to compute nV/sqrt(Hz)?
Thank you
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