#186 Oscilloscope Bandwidth and Sample-Rate Explained with Test

Practice test.. bandwidth and sample rate an eye opener for me.

[raymonddompfrank]

Sorry, this was originally posted as a reply to Simon's reaction, where it doesn't belong.

This is a nice explanation for real-time sampling but almost all but the very cheapest modern 'scopes are capable of performing "equivalent time sampling" (ETS).

This implies that, unless I'm very mistaken about what the 'scopes in the video are capable of, assumed relations in the video between the not-so-steep edges and their "limited" maximum real-time sample rate do not exist. The edge speeds shown are limited by generator capabilities, 'scope analog bandwidth and impedance matching.

No relationship exists between maximum sample rate and "analog" bandwidth, if the ETS is high enough.
The reason for this is that using equivalent-time sampling, multiple periods of a signal together are used to construct one waveform for displaying. Samples from multiple sampling periods are interleaved. Only the sampling time, i.e. the time the 'scope looks at each and every individual sample, must be short enough.
This interleaving has nothing to do with AD converter(s) being interleaved.

Using ETS, the highest frequency that can be shown isn't at all dependent on a 'scope's maximum real-time sample rate nor its storage rate. ETS is usable on any repetitive signal, if the 'scope supports it. That's why even many really old 70k Sa/s (yes!) sampling 'scopes show a signal's 50 ps rise time, no problem, just not "single-shot", i.e. not if a one-time event. Many early digital 'scopes had such low sample rates that sampling a waveform of even as low as say 10 MHz in one go wouldn't have been possible.

ETS can be many hundreds of times the maximum real-time sample rate. With most "serious" modern DSO's, maximum real-time sample rate is shown on their front.

A bit more technical: The Nyquist limit applies to the number of samples necessary to define one complete sinusoidal period (not an edge) and does not apply to ETS in that way.

[SINHRO-FAZA]

Отличное видео с примерами в нюансах работы цифровых осциллографов..

[qzorn]

The Siglent oscilloscopes: SDS1204X-E 4 Ch 200MHz, SDS1104X-E 4 Ch 100MHz, SDS1202X-E 200MHz 2 Ch, all are [1 GSa/s], and no faster option.
memory depth varies. 7 Mpts/CH (non-interleaved) 14 Mpts/CH (interleaved) I am not sure if the 200MHz scope is the way to go? 😎 Thank you Tony. Great information.

[SoddingaboutSi]

Gets all complicated with Nyquist frequencies when running out of sample rate. Well explained Tony. When using fast risetimes on the scope termination becomes very important.

[smith.randall]

Wow! Great vid. I feel like I never understood anything at all until now 😂

Very nice! Nice shirt too 😀

[gtretroworld]

The Siglent is clearly in a different league, thanks Tony.

[wernerpeter]

The 5 measuring points per period are correct, but these points are always positioned differently. They are not always in the maximum, minimum and zero crossing. Now it depends on the intelligence of the firmware to interpret a waveform here. You can also switch the presentation from vector to dots to see the sample points. I also find the oscilloscope's memory depth to be important in order to save the samples over a larger time frame. The OWON has options in the menu to minimize this restless display. A very nice representation of these parameters, great video 👍

[rrb]

My first test equipment was a RIgol 1054Z. Great machine, but when I began my UHF vintage lab it becomes a secondary friend, I use the SA a lot more. The Rigol is still useful for tiny signals inside of the big fellas from HP :) great video Tony

[TRONMAGNUM]

Owon is not bad for budget hobbyist. The Siglent is much higher quality. Very good video.

[vachik]

Very very good! A minimum of water, a maximum of facts.
Thank you.

[allthegearnoidea]

Lovely to see all your oscilloscope. I only have 17 so room for a few more I think.

[englishrupe]

Real thanks for explaining and showing this!

[PEGVK]

Very good video!
Tony, Keep on with the GOOD WORK!

[LockdownElectronics]

Excellent demo, very useful, thank you.

[derdoktor]

Hi Tony,

I like your videos (and your efforts to connect all and everything to your 10 MHz time base) 😀

One not so expensive suggestion for front end measurements of scopes.

When I got my new Siglent SDS2000x plus I was keen to measure the “new” bandwith via rise time.

But no generator I own was able to provide the needed fast pulses.
From the EEVblog forum I got the hint to buy a Leo Bodnar pulser. It came with a measured
rise time of about 50 ps. Than it is easy and more reliable to check the BW of the front end of your scopes.

[yuriantunes]

Loved the video, good content and now i know how good the owon oscilloscopes are.

[ernestb.]

Maybe you could turn off the interpolation sin(x)/x to show the real signal. I do not know what options these scopes have. I know Tekronix has for example the Dots-only mode, where you an see the actual samples. There should be at least 2 ways to interpolate, sin(x)/x and Linear. We can see in your video that the scope is using the sin(x)/x interpolation. At the end you end up with a sinus signal no matter what signal you put in. An analogue scope would have a similar problem. Not using the interpolation, but the rise time decay/limit would also make a sinus out of a square wave if freq. high enough. But I suppose you could go much further above the bandwidth. The amplitude would go gradually down of course. Nice scopes those Siglents. No Owen for me 😁

[catgirlamy]

this was quite helpful.

i've been shopping for a cheap hobbyist bench setup as i'm mostly working with audio and some digital signals (<10mhz) and i thought i might be able to get away with a 20mhz scope, but i'll make sure to get at least 100mhz.

i'm gonna watch some more of your videos, tho i have a little trouble understanding you because of the audio quality and accent, hopefully one day you'll get a really good mic setup figured out, and hopefully i'm around to see it.

thanks :)

[Andrewausfa]

Good video Tony. I've been thinking of getting a new modern scope but there is definitely more to buying one than just the MHz specifications. For the things I work on, old radios and test equipment, probably not much effect with the bandwidth limitations but still very interesting to see this demonstrated. Regards - Andrew

[bogdan]

Siglent use persitence mode by default that's why the signal looks better