Products > Test Equipment

Bandwidth limit on Siglent SDS2000X Plus oscilloscope

<< < (7/8) > >>

Martin72:

--- Quote from: Martin72 on July 20, 2023, 04:57:34 pm ---Once again I'm too stupid to do it and can't get it to work on my HD, it looks just like it did on the X+.
But since 2N3055 showed it with an HD(didn´t find the thread so far), I assume it's my stupidity. 8)

--- End quote ---

Yepp it was... ;)

https://www.eevblog.com/forum/testgear/math-problems-on-sds2k-(trying-to-display-bandwith)/msg4972270/#msg4972270

Now I´m curious if this will also function on the SDS2000X+ after several firmwareupdates.
Will check it when I´m back to work or someone could check it before.

tautech:

--- Quote from: Martin72 on July 21, 2023, 07:57:39 pm ---
--- Quote from: Martin72 on July 20, 2023, 04:57:34 pm ---Once again I'm too stupid to do it and can't get it to work on my HD, it looks just like it did on the X+.
But since 2N3055 showed it with an HD(didn´t find the thread so far), I assume it's my stupidity. 8)

--- End quote ---

Yepp it was... ;)

https://www.eevblog.com/forum/testgear/math-problems-on-sds2k-(trying-to-display-bandwith)/msg4972270/#msg4972270

Now I´m curious if this will also function on the SDS2000X+ after several firmwareupdates.
Will check it when I´m back to work or someone could check it before.

--- End quote ---
Try on P2 in the SDS2000X Plus thread:
https://www.eevblog.com/forum/testgear/siglent-sds2000x-plus-coming/msg2787168/#msg2787168

Performa01:

--- Quote from: BillyO on July 21, 2023, 02:56:57 pm ---
--- Quote from: Performa01 on July 21, 2023, 10:29:43 am ---You can tell that I've never worked with that formula, always used accurate frequency response measurements instead.
--- End quote ---

That formula is based on the physics of the system.  Provided you can mathematically characterize the system's response you can work out a version of that formula for it.  It should be quite accurate.   Gaussian response is well characterized and the resulting 0.35/risetime is accurate.  For moderately flat response systems (the top end of most mid-range PGA/VGA) the response is also well characterized and 0.4/risetime is also accurate. 

--- End quote ---
Nobody said the formula isn't exact, yet as long as the frequency response is unknown (i.e. as long as it is not properly plotted with a levelled signal generator), the factor in that formula is unknown as well. This is where the cat bites their own tail.


--- Quote from: BillyO on July 21, 2023, 02:56:57 pm ---Using a sine wave generator has it's perils.  Unless you have calibrated it and are confident in it's performance it can also give very skewed results.  Ideally you would measure it's output and normalize it before taking each data point of the DUT to ensure it is flat at the frequency being tested.  The rise time is a single measurement and is accurate as long as the character of the response of the DUT is known.

--- End quote ---
Come on. I was talking about signal generators, not toys from ali express. Especially higher end ones have excellent flatness, all the more so when only the range up to about 500 MHz is really important, as for the usual entry level DSOs discussed here.

I even demonstrated the accuracy and amplitude flatness for both the Siglent SDG6052X AWG and my Anritsu MG3633A signal generator here. I think this should be flat enough for characterizing a scope bandwidth:
https://www.eevblog.com/forum/testgear/siglent-sdg6000-series-awg_s/msg2621457/#msg2621457


--- Quote from: BillyO on July 21, 2023, 02:56:57 pm ---
--- Quote from: Performa01 on July 21, 2023, 10:29:43 am ---There were several reasons that got my thinking wrong - ridiculous bandwidth claims being one of them.
--- End quote ---
Like the over 600MHz for a un-corked SDS2000X-P?  As an example mine has a rise time of 660ps, not the 800ps claimed by Siglent.  Using the formula (0.4/risetime) we get a BW of 606MHz.  Using a sinewave sweep @ I got 650MHz .  That 606 MHz does not look like a ridiculous claim to me.  The difference is probably got to do with my not being able to determine if the sine wave generator was flat.

--- End quote ---
I think I have alredy stated that the actual bandwidth exceeds the specifications, especially in the entry level DSOs.
As I've posted many times before, my own measurements resulted in ~570 MHz - and I have not taken the cable loss into account, which was about 1 dB @ 500 MHz. There was no need to, in my book, because this gives some safety margin for "guaranteed results", so to speak. If we add that one dB and look at -4 dB, we are at about 605 MHz.

650 MHz on the other hand sounds not very realistic, yet not ridiculous either.


--- Quote from: BillyO on July 21, 2023, 02:56:57 pm ---
--- Quote from: Performa01 on July 21, 2023, 10:29:43 am ---It looks very different for a higher bandwidth scope like the SDS6000A. The 0.35 factor fits for the 1 GHz model, but nothing else matches.

--- End quote ---
I imagine the 500MHz license on the 6000 series has much better performance than advertised.  As for the 2GHz version, it is most likely using more advanced PGA/VGA with more agressive flattening.  Tektronix claim .45 for their "maximally flat" response so 0.46 seems very much in line with that.

--- End quote ---
The hardware is the same for all SDS6000A devices.
I've tried to explain numerous times, why artificial bandwidth limits have high tolerances. So you can bet that pretty much all SDS6204A will have an actual bandwidth of about 2.2 GHz, but there might be quite some variation for the artificially bandwidth limited 1 GHz and 500 MHz models. The only safe bet is that the bandwidth of those will exceed the specification - but the amount could vary a lot.

Performa01:

--- Quote from: mawyatt on July 21, 2023, 04:07:19 pm ---Amplitude Brickwall Filters are not realizable but the analog IIR high order Chebyshev, Inverse Chebyshev and Elliptical filters produce a good approximation at the expense of highly non-linear phase response, FIR digital filters do even better. One issue for scope use of one of these analog filters would be the highly non-linear Group Delay (derivative of phase with frequency) associated with these type filters, whereas the less Brickwall like Bessel and Gaussian have a much better Group Delay which is very important for scope use and why they are usually employed. Of course the Digital FIR filters can disconnected the phase/delay and amplitude responses, which is a huge benefit in some applications.

--- End quote ---
That's the key. We cannot do anything but Gaussian (or Bessel, at most) at the analog side, otherwise the step response gets awful and pulse fidelity is lost. Yet you can do it digitally – a FIR filter can actually approximate a brick wall and still have constant group delay. High End scopes combine analog and digital filters to optimize their frequency and phase response. But this requires a sufficiently high sample rate to bandwidth ratio – the usual factor of 2.5 in modern top models (within their class) will not allow an effective digital filtering, if only because of the ineffective AA-filtering in the analog frontend.

gf:

--- Quote from: Performa01 on July 20, 2023, 04:22:46 pm ---With modern DSOs and their advanced features we can even let the scope plot its own frequency response, see the example for the SDS2504X Plus below.

--- End quote ---

Apparently just a FFT plot. This, of course, requires a stimulus with a flat spectrum in the frequency region of interest. May I ask what stimulus you used for this test? Sinc pulse? Chirp pulse? If you used a chirp pulse, how did you tweak it to avoid Fresnel ripples?

Navigation

[0] Message Index

[#] Next page

[*] Previous page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod