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

[Mechatrommer]

However this was a running capture, not one from Stop mode where many fewer dots get shown.

analyzing those fewer dots may reveals whether the scope showing sampled data only, or sampled data along with interpolated data, like Lecroy snapshot is combination of vector and dots, but the dots are interpolated data.

Want some special screenshot ?Just ask.

it will not hurt to post related stuffs. if you can plot as close as possible as Lecroy capture (vector + dots) or dots only maybe can add value to the thread or the "marketing" but for me, data gathered are already adequate, and my points are conveyed hopefully. cheers.

[tautech]

However this was a running capture, not one from Stop mode where many fewer dots get shown.

analyzing those fewer dots may reveals whether the scope showing sampled data only, or sampled data along with interpolated data, like Lecroy snapshot is combination of vector and dots, but the dots are interpolated data.

Want some special screenshot ?Just ask.

it will not hurt to post related stuffs. if you can plot as close as possible as Lecroy capture (vector + dots) or dots only maybe can add value to the thread or the "marketing" but for me, data gathered are already adequate, and my points are conveyed hopefully. cheers.

Dots are the raw sampling points, nothing else. This I can prove.
One complete period from the 10 Mhz Bodnar enough ?

[Mechatrommer]

it will not hurt to prove, but i trust you already. this is basic stuff which everyone already know. please do so if its not too much hassle for you (i hate asking people to do more than what i need) cheers.

[tautech]

A selection, mostly dots but some vectors when we need compare.
Toggled captures between Dot and Vector mode.
Most in Stop mode but a few running, all easy to identify.
Any in Stop mode are also toggled between Dot and Vector mode.
Max at 200ps/div. Dot count in the Timebase tab.
All in Auto memory management mode.

Please stop this BS about dot interpolation.

[Fungus]

then that probably causal... a real signal. who knows whats inside semiconductors IC?

Substrates that can predict the future? 

[ebastler]

then that probably causal... a real signal. who knows whats inside semiconductors IC?

Substrates that can predict the future? 

Come on, guys. A digital FIR filter (which may cause pre-ringing) cannot see into the future either when it processes a stream of digital amplitude values. It introduces a delay. The main edge appears delayed on its output, while some pre-ringing effects appear with less delay. No magic required.

[gf]

A selection, mostly dots but some vectors when we need compare.
Toggled captures between Dot and Vector mode.
Most in Stop mode but a few running, all easy to identify.
Any in Stop mode are also toggled between Dot and Vector mode.
Max at 200ps/div. Dot count in the Timebase tab.
All in Auto memory management mode.

Does run mode superimpose multiple traces on the screen, even though Persistance is off?
Apparently it does. How many traces?

Please stop this BS about dot interpolation.

In run mode (e.g. ..._9.jpg) there still seems to be some interpolation going on. Not interpolation in the traditional sense, but trigger point interpolation, aligning the traces horizontally by fractional sample time offsets. Since this signal is not undersampled, the trigger point interpolation is expected to work quite well here, and apparently it does. But I wonder how well it works if the edges were undersampled?

[rf-loop]

It goes (least in Siglent) just as in theory
Look Fungus... Sinc is predicting... heh

Sorry these very small real raw dots is bit difficult to see... specially after GIF animation processed.
I have used Zoom mode for get more low samplerate just for make this thing more visible and also because at this time just now I do not have suitable signal source with enough fast edges so that can demonstrate this using higher speed. But how ever it do not change math.
Acquisition and after then oscilloscope stop and visible only last single acquisition.

After then changed modes: Dots only, Sinc, Linear.

Siglent do not have this kind of linear mode where is added interpolated extra dots between real dots. Only line what connects sample dots.
Sadly there is also not display mode where real dots can highlight when Sinc or Linear interp.

In some situations it is very good if we have opportunity to turn Sinc off when ever, run time or stopped or captured to history buffer and independent of what are other settings (sadly there is also oscilloscopes where this is not possible).

[Fungus]

In some situations it is very good if we have opportunity to turn Sinc off ... (sadly there is also oscilloscopes where this is not possible).

Happily: I don't know any where you can't have a sample rate far above the bandwidth of the input BNC.

[Fungus]

I love how everybody is busy trying to recreate a technique that was abandoned years ago in favor of sinc:

https://www.tek.com/en/documents/application-note/real-time-versus-equivalent-time-sampling

[gf]

I love how everybody is busy trying to recreate a technique that was abandoned years ago in favor of sinc:
https://www.tek.com/en/documents/application-note/real-time-versus-equivalent-time-sampling

Not recreate, but emulate -- without the expenses for a hardware trigger circuit and TDC that used to be required for ETS and its variants in the past. Particularly for low-end scopes it was certainy a cost factor. Digital trigger is cheaper, as it is just software on the FPGA, and offers more oportunities. But in the past when real-time sample rates were only in the order of 100MSa/s, one could hardly renounce ETS.

[Mechatrommer]

Please stop this BS about dot interpolation.

your tone is a bit too high for a representative didnt you still get it that Lecroy scope that i attached earlier shows interpolated dots? do you call them BS? i wish there is option to only shows sampled data, instead of many interpolated data that are too good to be true. but SDA6000 cannot be easily turned on right now and i havent played much time with it. still i would love to pull data from it raw which i have not yet.

on the topic of interpolation, i had play with some techniques in photo 2D and 3D object rendering (graphics) such as bezier, spline, bicubic curve etc... bezier is unsuitable for DSO purpose as interpolated data will not cross true sampled data, but interpolator like spline is good candidate as sampled data is included in the interpolated data. since Sinc in its limited resources form apparently doesnt make a good job anyway, maybe investigation into other method from graphics arena can be done, i think i will have no time for it. although spline may not recreate high order frequency such as in Gibbs Phenomenon, but it could be a safer bet on limited BW and sampling rate system, although Sinc is theoretically sound in data sampling arena, but in its limited form i would say it just possible for it to do a "wild guess" on what the signal should looks like, enough for now. people can google themselves on several data interpolation methods if they are interested cheers.

what most relevant to me are snapshots from tautech below, because it proved the scope is honest enough to reveals its sampled data without interpolation. and from there we can mentally figure that there are indeed ringing on the rise time. the rest of pics are just overlapped dots thats confusing to analyze. and the third pic below in vector also can help brain visualize to suspect if there is ringing or not. if from dots we dont see up and down much, there is no high freq near nyquist exist, so try to imagine there is ringing is just a wild guess. Sinc theoretically will be able to reconstruct the signal acccurately given 2 conditions (1) bandwidth of input data is limited with brickwall filter at nyquist freq, even a slight magnitude can screw it up and renders theory unapplicable (2) infinite parameters (or whatever practical the screen can show) is used. i suspect the visible gibbs effect is due to "not enough parameters" in Sinc interpolation OR BW filter of front end (analog) is not match brickwall at nyquist, any excess BW MUST be zeroed before it reach ADC! imho. i cant be sure about Sinc parms being not enough, i'm not a Sinc interpolater programmer, but what i'm certain, its not perfect implementation in some DSO condition. this is why also if sampled at much lower rate, by theory, "a properly designed" DSO should also switch BW limiter to match nyquist limit, such as if sampling at 100MSps, BW limiter must be brickwalled as well at 40-50MHz, at 10MSps, brickwall at 5MHz etc... do you think its easy for DSO designer? fwiw...

[Mechatrommer]

then that probably causal... a real signal. who knows whats inside semiconductors IC?

Substrates that can predict the future? 

looking at tautech pics (1st and 3rd picture in my post just above)...there is rippling before event, many other things can happen such as mismatch and reflection, but need to look further what happened before the snapshot. same thing on the rise area there are infinite rippling to the end of pic. waves and interactions with parasitics (pcb and components) is a mystery things.

[2N3055]

My biggest problem with your posts is that I cannot, for the love of God, figure out what the heck you are trying to say and prove.

You post a flurry or unconnected statements, insults and misrepresented data and then when people reply to you,  you follow up with more of the same.

You keep talking about interpolated dots in LeCroy without explaining to people that LeCroy scopes have Enhanced sample rate mode (ESR), that is upsampling by factor of 2, from 5GS/s to 10GS/s. That being a controversial point is irrelevant. If you don't like it,  just disable it and stop bitching about it. I also prefer not to use it, for various reasons.

That being said, SDS6000A also supports ESR. SDS2000X HD does not. My images also show SDS6000 data WITHOUT ESR.
That is one confusion out of the way.

As for Sin(x/x) reconstruction , that is ONLY proper way to reconstruct signal if you cannot afford to have oversampling that is pretty much factor of screen resolution. That means that you should at least have one sample point per pixel on screen, and then you don't need interpolation.
For a screen 1000 pixels wide, you would need 100 samples per division. On 1ns/div that means 100GS/s. Good luck with that.
So sampling theory to the rescue.
Sin(x/x) reconstruction filter is our friend. Math works. Those who don't understand that, back to school.

[wasedadoc]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

The filter is a low pass video filter.  Yes this one has many Ls and Cs.  I don't say it is necessary to have such a complex filter to show the effect. Just that this is a filter that I still had up in the loft from prior to 1980 when I was designing some video equipment and I knew it would certainly be suitable for this demonstration.

The input is a 100kHz square wave.  Shown on CH2 and and the scope triggered on it.  Generator is a Uni-T UT962E whose rise and fall time is not less than 15ns.  The output impedance is 50 Ohm whereas the filter is designed for 75 Ohms in and out and that is quite critical.  Hence the parallel 56 Ohm and 47 Ohm in series on the input and the 75 Ohm resistor across the output with the CH1 probe across it.

Scope is Rigol DS1054Z enhanced to 100MHz.  The 20MHz BW limit is not enabled on any channel. CH3 is turned on but not used.  This is to enable the button to turn off sin(x)/x on the scope.  Sampling rate is 250Msa/s.  Vector mode or dot mode does not change the ears.

The delay through the filter is about 1.2 us.  The "left ear" around each transition begins at the same time as the input transition.

[nctnico]

Nope. Your scope is showing the real signal. Not 'virtual' Gibbs ears. The dead-giveaway is that the signal doesn't change between vector, dot and sin x /x mode.

[Fungus]

Scope is Rigol DS1054Z enhanced to 100MHz.  The 20MHz BW limit is not enabled on any channel. CH3 is turned on but not used.  This is to enable the button to turn off sin(x)/x on the scope.

Just a note: The trick of turning on three channels on a DS1054Z to enable the menu item that says "sin(x)/x on/off" doesn't really work.

It replaces sin(x)/x with a different filter, but it's still a filter. You do NOT get raw data by doing that.

It's much better to turn off channel three and get double the sample rate.

[Mechatrommer]

As an example I can show 10 MHz square wave signal, sampled at very low 25MS/s in dot mode. Signal is band limited with 200 MHz filter, so there are no frequencies (odd harmonics up to 19th in this case) above that. Simple edge trigger. Scope is my Siglent SDS6000.
Reference image is same signal, just sampled at 5GS/s.

Signal sampled with 25MS/s is perfectly reconstructed.
Can you explain why?

Let's start with that. Then we will proceed from there. Explain that first.

sorry i miss this post... i was distracted by other posts

from eyeballing your picture, sampling at 25MSps, nyquist limit is 50MHz, but you claimed 200MHz limited. by theory, its should already violates nyquist law and unable to reconstruct, yet you showed perfect reconstruction, somethings not right. is your scope can switch down to 50MHz BW at front end? i'm unable to make conclusion, not enough data and something not add up, such as....

in your other "properly designed" scope, even 100MSps sampling on "properly cutoff" 200MHz scope, it cannot reconstruct 1MHz square accurately, we got nasty Gibbs! can you answer why? before i can make firm conclusion. here comparison:

1) sampling 10MHz square, 25MSps = perfect
2) sampling 1MHz square, 100MSps = bad
why? please elaborate. i suspect you hide some setup i'm not aware of... you didnt explain anything in your post where i usually linked.

[Mechatrommer]

LeCroy scopes have Enhanced sample rate mode (ESR), that is upsampling by factor of 2, from 5GS/s to 10GS/s. That being a controversial point is irrelevant. If you don't like it,  just disable it and stop bitching about it. I also prefer not to use it, for various reasons.

10GSps quad channel, 20GSps dual channel to be accurate, and i've disabled that feature in screenshot, you can see. where did you get SDA6000 upsampling from 5GS/s to 10GS/s? its also in the setup picture cant you see?

Those who don't understand that, back to school.

who's insulting who? and who got insulted? (by facts) are you trolling so this thread can get locked? by involving your unstable emotion here? answer academically please.

[Mechatrommer]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks! i didnt rule out the possibility of it existing... so thats why i asked for evidence. if we have yellow trace only, we could have mistakenly assume its non-causal Gibbs effect, but actually its causal real Gibbs. from picture its about 1us delay. mind to tell what filter is that? or if that feasible to put on DSO front end?

[nctnico]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks! i didnt rule out the possibility of it existing... so thats why i asked for evidence. from picture its about 1us delay. mind to tell what filter is that? or if that feasible to put on DSO front end?

Again, what wasedadoc is showing are not Gibbs ears!

[wasedadoc]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks! i didnt rule out the possibility of it existing... so thats why i asked for evidence. from picture its about 1us delay. mind to tell what filter is that? or if that feasible to put on DSO front end?

Again, what wasedadoc is showing are not Gibbs ears!

What are they then?

[Mechatrommer]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks! i didnt rule out the possibility of it existing... so thats why i asked for evidence. from picture its about 1us delay. mind to tell what filter is that? or if that feasible to put on DSO front end?

Again, what wasedadoc is showing are not Gibbs ears!

dont be pedantic friend... if someone give your kid an elephant toy and they call it ohh its an elephant! and then you say, its not an elephant, elephant is in jungle, you screw it man.. ok fine! it just looks like Gibbs ear, but not Gibbs ear... or else what proper term for it? ever-increasing-magnitude-apparently-seems-non-causal-ringing? cheers.

[Fungus]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks!

Those aren't Gibbs ears.

(because the circuit is NOT ringing before the pulse occurs)

[Mechatrommer]

Here is some evidence that Gibbs ears are real and can be seen on the output of a passive analogue filter.

yes! i was about to sketch similar picture for Fungus to understand, but since you provided proven one, thanks!

Those aren't Gibbs ears.
(because the circuit is NOT ringing before the pulse occurs)

here attached for your sharp and trained eyes... input is blue, but given we dont know it exists. similar if its like in the IC, who knows? yes its not Gibbs, but we could be mistakenly think is...