Simple Technique to measure Waveform Update Rates: DSOs w/either Edge Triggering

[marmad]

Just to clarify - since there seems to be some misunderstandings here - for this technique to work with a DSO, it must support EITHER (Green) Edge triggers (which I thought was common, but now seems to be limited to higher-cost DSOs), not ALTERNATE (Red) Edge triggers (which seems to be what is implemented in cheap DSOs)

...which means it does nothing else than simply re-arm trigger with different edge value.

Yes, this sounds like alternate Edge - which introduces logic into the situation - instead of just triggering on every edge, whatever it may be.

[jpb]

I don't know what the buffer arrangements are but on their earlier scopes they used multiple DACS and perhaps they have two banks of 8x128bytes of high speed memory on the front end which is filled alternately and only transferred to slower memory when it is filled. So that they effectively have 2 very high speed 1k buffers which are switched between with one being filled whilst the other is being emptied into slower RAM.

The architecture (post-ADC) of the DS2000 is VASTLY different; it is in no way similar to the earlier DS1000E series - which used the same 512kB*8B SRAM as sample AND display memory. The DS2000 has 3x 32MB*16B DDR2 for sample memory, as well as 2x 512kB*36B display SRAM. The image (from Dave's teardown) shows the ADC (bottom), FPGA (heat-sinked), and the DDR2.

OK I accept that the architecture is different, but I am convinced that there is some sort of high speed 1k buffer probably within the FPGA - (for comparison  Dave has mentioned that Agilent has all their memory in the FPGA to allow high speed) - which restricts the granularity of sampling to 1024 samples as a minimum unit.

DDR2 likes data to be transferred 64bits at a time, the DAC is producing 8bit samples but at very high speed (i.e. 2GS/s) so there must be some sort of buffer with 8bits x 2G in and 64bits x 250M out, in fact DDR2 can go up to 3.2GB/s with a 100MHz clock but it needs to be 64bits wide to reach this.

Some sort of buffer is needed, I'm just postulating that this buffer is 1024bytes.

[tinhead]

...which means it does nothing else than simply re-arm trigger with different edge value.

Yes, this sounds like alternate Edge - which introduces logic into the situation - instead of just triggering on every edge, whatever it may be.

i was just about to write "fuck, can you not just read what i wrote? bit less emotions and few more seconds to read
what others wrote is more useful" .. and before i did it, you posted this

[marmad]

DDR2 likes data to be transferred 64bits at a time, the DAC is producing 8bit samples but at very high speed (i.e. 2GS/s) so there must be some sort of buffer with 8bits x 2G in and 64bits x 250M out, in fact DDR2 can go up to 3.2GB/s with a 100MHz clock but it needs to be 64bits wide to reach this.

Some sort of buffer is needed, I'm just postulating that this buffer is 1024bytes.

Possibly. Although, since the Rigol's sample memory really is divided into units of 7 (7kPts per channel), and the Spartan-6 has 8kB (no parity) of dual-ported RAM, 8192 bytes might be a better guess. 

[marmad]

i was just about to write "fuck, can you not just read what i wrote? bit less emotions and few more seconds to read
what others wrote is more useful" .. and before i did it, you posted this

Sorry - sometimes people don't hang around after posting, and since, at the beginning of your post, you mixed-up the trigger types that I meant, I just wanted to point that out quickly in case you were 'leaving' to run other tests. But I did go back and finish reading your post 

So I guess it was just a misunderstanding because of semantics? An "alternating Edge Trigger" as opposed to an "Alternate Edge Trigger" (or "Alternate Trigger in Edge mode")? 

[tinhead]

easy to test at 10ms/div. If your DSO does not produce an un-moving waveform with 1, 2, 3, 4, or 5Hz - then it IS NOT triggering on every edge

out of curiosity, is it working as well with single shot mode on Rigol DS2000 ?

So I guess it was just a misunderstanding because of semantics? An "alternating Edge Trigger" as opposed to an "Alternate Edge Trigger" (or "Alternate Trigger in Edge mode")? 

exact, that was the case.

[KedasProbe]

I tried it on my Hameg HMO1022 it also has no trigger out, and it seems it also uses alternate trigger for 'Slope=Both'.

[marmad]

out of curiosity, is it working as well with single shot mode on Rigol DS2000 ?

If I do a single shot with a 1Hz square wave coming in, sometimes I will see the rising edge - sometimes the falling edge - it just depends on which edge happens to trigger the acquisition when I press 'Single'.

[marmad]

I tried it on my Hameg HMO1022 it also has no trigger out, and it seems it also uses alternate trigger for 'Slope=Both'.

That's too bad    But the Hameg has some nice triggers - maybe there's an alternative; I'll glance through the manual.

[tinhead]

out of curiosity, is it working as well with single shot mode on Rigol DS2000 ?

If I do a single shot with a 1Hz square wave coming in, sometimes I will see the rising edge - sometimes the falling edge - it just depends on which edge happens to trigger the acquisition when I press 'Single'.

hmm, even when you set signal source to short pulse (short enought to be shown complettly on display) each every 1Hz?

Just thinking how can Rigol DS2000 trigger on either edges when it does only on "which ever first" (as you said right now),
which looks like then like alternate

[jpb]

DDR2 likes data to be transferred 64bits at a time, the DAC is producing 8bit samples but at very high speed (i.e. 2GS/s) so there must be some sort of buffer with 8bits x 2G in and 64bits x 250M out, in fact DDR2 can go up to 3.2GB/s with a 100MHz clock but it needs to be 64bits wide to reach this.

Some sort of buffer is needed, I'm just postulating that this buffer is 1024bytes.

Possibly. Although, since the Rigol's sample memory really is divided into units of 7 (7kPts per channel), and the Spartan-6 has 8kB (no parity) of dual-ported RAM, 8192 bytes might be a better guess. 

OK here's my latest thought - the 2000 series shares an architecture with the 4 channel 4000 series so the 8k is split into 2 buffers per channel (allowing one to empty while the other is filling) for 4 channels giving the 1k buffer size! I'll now stop. 

[marmad]

Just thinking how can Rigol DS2000 trigger on either edges when it does only on "which ever first" (as you said right now),
which looks like then like alternate

An 'alternating' Edge trigger means that EVERY trigger begins with a Rising edge and ends with a Falling edge - Or that's what I had been thinking earlier (but, of course, no simple DSO to check it on). The other possibility is that it just triggers on the next available alternate Edge.

An 'either' Edge trigger means that it triggers on ANY incoming edge - alternate or not.

The DS2000 also has the Delay trigger - with two possible sources - both of which can be set to either Rising or Falling edge - and any channel - so you can have alternate Rising edges - or alternate Falling edges - trigger the DSO.

[Deckert]

Hi,

Just for completeness sake, here are the trigger modes, as explained in the manual for the Siglent/Atten.

--deckert

[ivan747]

I haven't been able to find the blind time on my DS1102E. I've been trying for hours. Time to check the manual. Maybe the trigger is not the same as the DS2000 series or I'm doing something wrong.

@ivan747: Well, I'm not 100% sure that the DS1000E series allows either rising or falling Edge triggering. Despite what I believed earlier, it's appearing more and more like cheap DSOs (and LeCroy ) don't offer this feature - and that it's only available on higher-end DSOs.

But you can tell very quickly by just going to the 10ms/div time base setting, then sending your DSO a square wave of 1, 2, 3, 4, and 5Hz. If one of those frequencies doesn't stop your DSO from triggering on both edges (and produce a stable, non-moving waveform), then the DS1000E series is doing alternating Edge trigger - instead of either Edge - and this technique won't work.

Doesn't work at all. Tested from 1Hz to 7Hz in 0.5Hz steps.

[marmad]

Just for completeness sake, here are the trigger modes, as explained in the manual for the Siglent/Atten.

It would probably be more clear if they used the word 'then' instead of 'and'.


Ugh I need food 

[ivan747]

I believe it's possible, as someone mentioned earlier, to achieve the same effect. On an oscilloscope that works using alternate edge triggering.



Just place a wave (square preferably) on channel one of a frequency F. On the trigger channel, apply a signal in phase, of a frequency 2F. Trigger on the rising edge of the Trigger channel. You should achieve the same effect as Marmad's original idea. I am trying this right now. 

Note: a good way to do this in hardware is a simple square wave generator( could be 555, function gen. or sound card) and a frequency divider using a flip-flop.

[Deckert]

Then I think the Siglent/Atten scope works differently to how you think it does. If the signal rises, the scope triggers. If the signal falls, the scope triggers. That looks like "either" (or OR) to me. It definitely doesn't wait an entire cycle before it triggers again.

However, the scope makes sure that I don't miss the falling edge, no matter what the timebase (or frequency) is. That sounds more preferable to me.

--deckert

[ivan747]

Cheers! Just tried my method and it works on the Rigol DS1102E. Tested on the 10ms timebase, both sine waves, trigger is at 4Hz and CH1 is at 2Hz, the waveform only displays the falling edge. It does this on 5Hz/10Hz (Ch1/Trig.).

My setup is very rudimentary, consisting of my computer, Audacity and some crocodile clips hooked to an RCA connector and probe hooks.

EDIT: that was with CH2 turned on. Now that I turned it off it behaves even more like the original post.
On 3 and 4Hz at CH1 only one edge of the trace appears. On 5Hz, it starts to alternate again.

Does anyone knows how to make a sweep stay in phase with another sweep of twice the frequency? I have a sweep generator in Audacity. I can specify amplitude, start and end frequency and if I want linear or exponential sweep.

[tinhead]

Then I think the Siglent/Atten scope works differently to how you think it does. If the signal rises, the scope triggers. If the signal falls, the scope triggers. That looks like "either" (or OR) to me. It definitely doesn't wait an entire cycle before it triggers again.

However, the scope makes sure that I don't miss the falling edge, no matter what the timebase (or frequency) is. That sounds more preferable to me.

--deckert

and this is exactly what HanTekway is doing as well, the single shot on DS2000 looks to me like it does exact the same
as well too. So probably in run mode DS2000 is simply triggering twice (on both edges, which was exactly what i
requested from Hantek as a fix for their current " both edges" implementation), which (i guess) could explain why on Rigol
one edge disapears when reached the blind time window.

[marmad]

Then I think the Siglent/Atten scope works differently to how you think it does. If the signal rises, the scope triggers. If the signal falls, the scope triggers. That looks like "either" (or OR) to me. It definitely doesn't wait an entire cycle before it triggers again.

But your scope won't trigger on two rising - or two falling - edges in a row; they have to alternate. And that's exactly how I think it works. And sorry, but no, that's not the definition of 'either' (i.e. every).

However, the scope makes sure that I don't miss the falling edge, no matter what the timebase (or frequency) is. That sounds more preferable to me.

Of course you're missing edges - more than with a true 'either' Edge trigger    That's why 'either' Edge exists - so you see as many edges as possible.

[marmad]

Ok - I got some food so I could think clearly again - and finish my diagram [correctly - I think!] 

@deckert:

This diagram shows a DSO needing both alternating Edges to trigger the acquisition;  the frequency of the input signal is just over half the inverse of the minimum acquisition time.
Note: red = accepted trigger / black = missed or ignored trigger / green-orange = blind time / gray = waiting for trigger

On the DSO with 'alternate', the waveforms per second becomes a quarter of the maximum rate.
On the DSO with 'either', the waveforms per second becomes half of the maximum rate (as shown in the video).




EDIT: (I had been thinking that the diagram above illustrated an 'alternating' Edge trigger - but it must be the one below since, according to reports, both edges remain visible.)

This diagram shows a DSO needing a single alternating Edge to trigger the acquisition;  the frequency of the input signal is just over half the inverse of the minimum acquisition time.
Note: red = accepted trigger / black = missed or ignored trigger / green-orange = blind time / gray = waiting for trigger

On the DSO with 'alternate', the waveforms per second becomes a third of the maximum rate - missing or ignoring 2 triggers between each acquisition.
On the DSO with 'either', the waveforms per second becomes half of the maximum rate (as shown in the video)  - missing or ignoring 1 trigger between each acquisition.

[darrylp]

Well 2.4.1sp2 firmware on an upgraded 1052e without sin(x)/x on gets a max of 20 wfms. Hmm. That's even down to 2ns timebase.

Turning on sin(x) reduces to 13 on some timebase and 14 on others.

The ds1052e on listed firmware does both triggering.

20 wfms from 50us downwards. msand higher timebases where down in single digit updates.

--
  Darryl

[onlooker]

So it is worse than Owon7102? Why didn't I see more talkings about this?  Just kidding.

[marmad]

Well 2.4.1sp2 firmware on an upgraded 1052e without sin(x)/x on gets a max of 20 wfms. Hmm. That's even down to 2ns timebase.

Turning on sin(x) reduces to 13 on some timebase and 14 on others.

The ds1052e on listed firmware does both triggering.

According to other DS1052E users in this thread, the DSO does not do 'every' Edge triggering - but instead does 'alternate' Edge triggering. If this is true, the video method does not work.

[darrylp]

well its working on mine ( hence mentioning the firmware on it )

the screen shows the same sort of imageas  in your video Marmad, when you first show the square wave. i can then get it to loose the left down trigger, and the counter (also with a T in the front of it, as I had the trigger on, and using the normal setting as per your DS2072 ) then goes squiffy.  ie. its showing double of my function gen input. then tops out around the 40Hz on the counter, but 20Hz on the FG. going higher on the FG and the counter on the scope goes down ...  not down to half, like you were seeing on the external trigger out, but down it goes. so 21Hz on FG shows 33.76Hz on counter ( that was one time i wrote down ) but not sure what timebase that was now.

ie wasnt using persistance vision, used vectors instead of dots, as only at low timebase where the dots mode usable on the 1052e for this test.