Products > Test Equipment

Sub: Rigol's DHO800 Oscilloscope (Gibbs Effect & Aliasing Misunderstanding)

<< < (39/48) > >>

Mechatrommer:

--- Quote from: Fungus on November 02, 2023, 07:01:41 am ---"Yaigol" was fixed by a firmware update about six months after launch.

--- End quote ---
yeah but who have time verifying new scope model?

rf-loop:

--- Quote from: Martin72 on November 01, 2023, 10:43:10 pm ---I had just discovered pictures of my Bodnarpulser on the Rigol DHO4204 which I had on loan, I put them here.
One channel active, 4GSa/s maximum sample rate, the signal looks "good".
Two channels active, 2GSa/s sample rate, the signal deforms a bit - but is "faster"(rise time)...
4 channels active, but still 1GSa/s samplerate, the signal looks a bit "blurred" in two places and the rise time becomes slower again.
Why is the bandwidth highest at 2GSa/s....

Bodnar_Single.png


--- End quote ---

I have one "question"...  ;)

When there is 10ns/div and 4Gsa/s (40 sample points / div) do we really need Sin(x)/x (aka Sinc) specially when oscilloscope is also 200MHz BW.

Think about it.

(yes I know where one other oscilloscope turn Sinc off (without indicating it) when some t/div is selected...and Sinc do not give any real advantage. Even when Sinc is still selected)

Also if I design oscilloscope I will really think carefully when Sinc give some advantage and when not...

Just for thinking..

gf:

--- Quote from: Mechatrommer on November 02, 2023, 05:32:00 am ---
--- Quote from: Martin72 on November 01, 2023, 10:43:10 pm ---Why is the bandwidth highest at 2GSa/s....

--- End quote ---
i guess because it produces cleaner less jittery Gibbs (Sinc interpolation) at 2GSa/s (200pts/screen 500ps/pts)? what surprises us is why the properly bw limited scope can still produce gibbs artifact at 10x sampling rate ::)

--- End quote ---

Keep in mind that any filter in the signal path with a sharp enough cut-off can introduce overshoot/ringing near edges, and if the filter happens to be a linear phase filter, then this ringing is symmetric (pre + post). This is not limited to sinc reconstruction filters, and it is not limited to undersampled signals.

In Bodnar_Dual.png (2GSa/s) I do not think that the pre- and post-ringing comes from an interpolation filter. An upsampling filter from 2GSa/s has a cutoff at 1GHz (or slightly below), and its ripples are supposed to have a period in the order of 1ns. But the period here is rather 2ns (or even a little bit more), which suggests that we see the result of a FIR filter with a cut-off < 500MHz. However, don't ask me what's the objective :-// And since the trace is pretty clean, I'm quite confident that it doesn't suffer from aliasing (at least not significantly), i.e. very likely it was properly bandwidth limited before sampling.

OTOH, I'm pretty confident, that the signal in Bodnar_Quad.png (1GSa/s) was not properly bandwidth limited before sampling and that the apparent (let me call it) "reconstruction jitter" is caused by aliasing.

Mechatrommer:

--- Quote from: gf on November 03, 2023, 11:07:40 am ---
--- Quote from: Mechatrommer on November 02, 2023, 05:32:00 am ---
--- Quote from: Martin72 on November 01, 2023, 10:43:10 pm ---Why is the bandwidth highest at 2GSa/s....

--- End quote ---
i guess because it produces cleaner less jittery Gibbs (Sinc interpolation) at 2GSa/s (200pts/screen 500ps/pts)? what surprises us is why the properly bw limited scope can still produce gibbs artifact at 10x sampling rate ::)

--- End quote ---
Keep in mind that any filter in the signal path with a sharp enough cut-off can introduce overshoot/ringing near edges, and if the filter happens to be a linear phase filter, then this ringing is symmetric (pre + post). This is not limited to sinc reconstruction filters, and it is not limited to undersampled signals.

--- End quote ---
show me in any rigol DSO, or any other "better" competitive DSO from teardown photos that have this "sharp enough cut-off can introduce overshoot/ringing near edges". one member here proved that filter exists, but not for DSO. even if it is, it will not fit from teardown photos evident, we dont see fancy inductors capacitors 3x 5x parellel networks over there. prove me wrong, and err... also care to explain why at 4GSa/s snapshots above got no overshoot/undershoot.pre or post ringing?


--- Quote from: gf on November 03, 2023, 11:07:40 am ---In Bodnar_Dual.png (2GSa/s) I do not think that the pre- and post-ringing comes from an interpolation filter.

--- End quote ---
nope! until evident provided. i've provided a few, its your turn... here's the challenge below if you miss it (on any brand scope thats capable both Sinc ON and vector/dot (Sinc OFF) mode. its like nobody understand this thread and i'm just talking to the air :palm: in fact the evident that there is no pre-ringing is just right above the 2GSa/s image, ie capture at 4GSa/s. how amazing people can miss it! ;D

https://www.eevblog.com/forum/testgear/split-from-rigols-new-dho800-oscilloscope-unbox-amp-teardown/msg5142249/#msg5142249






--- Quote from: rf-loop on November 03, 2023, 08:04:36 am ---I have one "question"...  ;)

When there is 10ns/div and 4Gsa/s (40 sample points / div) do we really need Sin(x)/x (aka Sinc) specially when oscilloscope is also 200MHz BW.

Think about it.

(yes I know where one other oscilloscope turn Sinc off (without indicating it) when some t/div is selected...and Sinc do not give any real advantage. Even when Sinc is still selected)

Also if I design oscilloscope I will really think carefully when Sinc give some advantage and when not...

Just for thinking..

--- End quote ---
not just when developing DSO, but PC SW that utilize sampled data, or even in graphics 2D 3D rendering will deal with this decision matters. like my SW just above. i let Sinc to take place when sampled points is less than screen size divide by 2.. this is developers decision.. maybe if (data_count < screen_size / X) then do Sinc, else do vector plot.... X can be 2,3,4,5? it depends on developers/designers... but user should decide if need Sinc ON? or want Sinc OFF? in any condition...

Mechatrommer:
here again i upgraded VisaDSO v1.1.3 to enable interpolated Sinc/Lanczos on single shot capture...see the difference. Leo Bodnar Pulse captured by DHO924 then data downloaded to PC... Sinc OFF (no Gibbs Effect) the boring straight line vector drawing mode, and Sinc ON (with Gibbs Effect) for noob's eyes satisfaction curvy plot. granted this is a scope that violates Nyquist at max sample rate and 4 channels, but for DHO4000 above, 2GSa/s single channel... its puzzling.

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