Rigol's New DHO800 Oscilloscope unbox & teardown

[2N3055]

In DHO series only ASIC is analog front end ASIC. Their ADC is not ASIC as much as local ADC source. That ADC can be replaced with any other ADC, and if you get good one at a good price, you can match them.

Actually believe the Rigol 12 bit ADC is more of an Application Specific ADC than not. Reasoning is that Analog Devices and TI ADC design targets a much broader range of applications than just the DSO, whereas Rigol may have reduced the initial design requirements, efforts, and cost with just the DSO product target. This allows relaxed specifications for the ADC in many areas and thus reduces the initial design task and costs. Of course we don't know for sure, and don't generally like to speculate, but do have some background here and some "hints". Would be very interesting to find the actual "wafer yield", but that's usually a highly regarded parameter and not going to be disclosed by Rigol or the IC fab.

Rigol still needs to utilize a boatload of these ADCs to recover the NRE, and likely the DSOs under discussion are the recipients of the lower grade ADCs from the chip testing fallout, where the higher grade ADC chips go the higher class DSOs.

Sure one could replace the Rigol ADC with a TI or AD 12 bit ADC and be done, but this would have a higher Recurring Cost and not achieve this attractive price point IMO.

ENOB, Linearity and so on will revel just how good these ADCs are. However, without a better FFT as R&S and Siglent have implemented, some of this might be difficult to properly access.

All this might not matter to the audience these lower cost DSOs are targeting and just having a 12 bit ADC with low noise front end, good screen resolution, and HDMI is enough. Being able to "see" finer waveform details and a nice Hi-Rez display may be all that matters to many whether they are "real" or accurate isn't important!!

A good set of tests would be in order. The classic 2-Tone IMD and another interesting test would be to utilize the math functions to evaluate precision waveforms and view the numerical results. Things like waveform average, RMS(SD), DC Levels and so on might hint at just how good the input channels behave over the ranges. We did such when we got our 1st SDS2000X+, and were pleasantly surprised how well it performed.

Anyway, fun discussions going on.

Best,

Thank you for summarizing it much better than what I ever could.

As for my "not really ASIC" comment for Rigol ADC I thank Asmi and you for education. I'm not in ASIC business so my use of terminology will not be correct. What I wanted to say is that while Rigol's ADC obviously is ASIC as a type of product because it is custom made IC that was made by company for their specific use, ASICs are usually made for a very specific function: a switching matrix for a high speed interconnect, a complete integrated sound engine for a synthesizer, or something like that.
In this case, Rigol made "just another ADC", a chip for which there is alternative. Of course that assessment is based on my limited knowledge from what Rigol has published. Maybe they did combine ADC and some sort of DSP to linearize response or something like that.. In which case it would be really single use application specific chip for scopes that could not be replaced easily. And would allow them to have simpler BOM and maybe make significant saving in FPGA resources and such...

But from what I see they still have same architecture as before with ADC-FPGA-App processor. So it seems any saving would be just in price of chip. I personally think it is more about control of sourcing the chip than good price (which is just a bonus).

[2N3055]

One of these FFTs isn't like the others...can you see which one?

Yeah, I have no idea what Dave did there... It is obvious that scopes are not set the same... Which is not surprise because Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters. I keep repeating that you need to either implement full RT Spectrum analyser (that does ALL of the necessary transformations from FFT to spectrum display) or a proper FFT mode where you have control over mathematical FFT parameters. 

[Fungus]

Rigol still needs to utilize a boatload of these ADCs to recover the NRE

I don't think that's going to be a problem. Rigol will have the hobby market to itself for the next couple of years at least and this thing is a big enough advance to make many owners upgrade their existing 'scope (eg. me)

and likely the DSOs under discussion are the recipients of the lower grade ADCs from the chip testing fallout, where the higher grade ADC chips go the higher class DSOs.

That doesn't follow at all.
a) You're assuming their chip yield is terrible when it's probably close to 100% and the ones that fail will likely be complete failures.
b) The "DSOs under discussion" will be the biggest sellers by a huge margin.

[Fungus]

Yeah, I have no idea what Dave did there... It is obvious that scopes are not set the same... Which is not surprise because Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters.

Uhuh, but there's a third 'scope there which does allow you to control all the parameters ... and it's agreeing with the Rigol.

[iMo]

..Yeah, but nicer to just have the results displayed directly on the DSO. ..

Sure, I've been talking the more detailed measurement only (to bypass the internal FFT such you get an unbiased result), not the actual FFT usage inside the DSO..

PS: the first step is to understand how the ADC (with the AFE) works, for that we need the data processed outside the DSO. Then the next step is to mess with the actual FFT implementation inside the DSOs - as its implementation depends on many params..

[2N3055]

Yeah, I have no idea what Dave did there... It is obvious that scopes are not set the same... Which is not surprise because Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters.

Uhuh, but there's a third 'scope there which does allow you to control all the parameters ... and it's agreeing with the Rigol.

So what you think which scope was not set up the same as the others ??

[dreamcat4]

yes, the siglentis fungicitus. very amusing 

[ebastler]

Yeah, I have no idea what Dave did there... It is obvious that scopes are not set the same... Which is not surprise because Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters. I keep repeating that you need to either implement full RT Spectrum analyser (that does ALL of the necessary transformations from FFT to spectrum display) or a proper FFT mode where you have control over mathematical FFT parameters.

Hmm. That sounds quite different than your outburst half an hour earlier:

Are you really that thick or you are paid to spew bullshit?
What is wrong with that FFT? It is slower because device has slower CPU. That is not a bug.
A 8 bit converter dynamic range is bug??

Muppet.

Did you actually watch Dave's video before you lashed out at Fungus? Care for an apology?

And speaking of Rigol's "FFT dummy mode": Maybe Siglent's "FFT expert mode" is not all that great, if Dave supposedly can't use it properly?

I appreciate your T&M expertise and the fact that you share it freely on this forum. But your continuous undercurrent of Siglent vs. Rigol bias does taint its value.

[Fungus]

Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters. I keep repeating that you need to either implement full RT Spectrum analyser (that does ALL of the necessary transformations from FFT to spectrum display) or a proper FFT mode where you have control over mathematical FFT parameters.

I assumed you knew what you were talking about but I just double-checked the manual and all the parameters seem to be there. Which ones are missing?

[ptluis]

No DOTS display?? only vectors? I wonder why?

[Martin72]

Looks nicer..

Which ones are missing?

Wait until you have it in your own hands. 
Before one example:
Where is the size setting ?

[iMo]

Guys, to be more constructive in comparing your DSOs - let you design a measurement, which may show some tangible data when running on the DSOs of your choice. It should be designed such the same settings are used, of course, and the data will be exported to the PC where you may use the matlab or whatever program for the analysis.
The next step is to compare the FFTs - here again you have to design the proper measurement as well.

[Fungus]

No DOTS display?? only vectors? I wonder why?

Dots used to be a thing on scopes with equivalent time sampling but we've moved on since than - sin(x)/x FTW!

[Fungus]

So what you think which scope was not set up the same as the others ??

You really think Dave didn't double-check the settings when he saw that?

[mawyatt]

Thank you for summarizing it much better than what I ever could.

As for my "not really ASIC" comment for Rigol ADC I thank Asmi and you for education. I'm not in ASIC business so my use of terminology will not be correct. What I wanted to say is that while Rigol's ADC obviously is ASIC as a type of product because it is custom made IC that was made by company for their specific use, ASICs are usually made for a very specific function: a switching matrix for a high speed interconnect, a complete integrated sound engine for a synthesizer, or something like that.
In this case, Rigol made "just another ADC", a chip for which there is alternative. Of course that assessment is based on my limited knowledge from what Rigol has published. Maybe they did combine ADC and some sort of DSP to linearize response or something like that.. In which case it would be really single use application specific chip for scopes that could not be replaced easily. And would allow them to have simpler BOM and maybe make significant saving in FPGA resources and such...

But from what I see they still have same architecture as before with ADC-FPGA-App processor. So it seems any saving would be just in price of chip. I personally think it is more about control of sourcing the chip than good price (which is just a bonus).

You are welcome!!

The ADC, or FPGA, is likely the single most expensive IC component in the DSO, and at this price point every $ in BOM matters. Without a custom in-house ADC, one is restricted to available chips from AD, TI and maybe some others, and don't think that anyone can get these ADCs at a price that would fit this price point.

We must remember that TI, AD and others have developed and produced high end performing ADC chips that satisfy many market segments, these incurred much higher development costs, and likely occupy more precious silicon area, involve extensive testing and so on. Whereas Rigol was able to isolate the important parameters that are more meaningful to the DSO market, trim the architecture to reduce the up front development costs, reduce the Si area, and so on.

Would wager that if we got ahold of one of these ADCs where we could do detailed isolated standalone chip testing, the overall performance would be mediocre in general compared to TI and AD. Things like no missing codes, monotonicity, differential & integral linearity, ENOB, aging, drift, temp, PSRR, and so on would not compare well with the TI and AD counterparts. Many of these parameters aren't that important in a DSO application, I mean who really cares if the ADC has a stuck lower bit, or non-monotonic around the LSBs, and so on. Now consider using this ADC as feedback in a complex high speed control system, stuck bits and non-monotonic behavior would be a disaster indeed!!

So Rigol likely (again we don't know), made a smart decision to create an ADC specific for DSO application use, with a main parameter of yield and recurring chip cost, so they could penetrate this low cost market. We're confident you won't see them selling these in the Open Market as a High Speed ADC tho.
 
Even with the targeted DSO application, they still had a difficult task ahead with the ADC design and apparently did an admirable job

Of course all this discussion is just hearsay and speculation on our part, but likely rooted with some substance

BTW the suite of tests you recommended earlier would be welcome by many, ourselves included. Lets hope that some qualified knowledgable folks can perform some of the tests

Best,

[Fungus]

Where is the size setting ?

One less parameter to juggle. 

What really counts is the resolution.

[nctnico]

Thank you for summarizing it much better than what I ever could.

As for my "not really ASIC" comment for Rigol ADC I thank Asmi and you for education. I'm not in ASIC business so my use of terminology will not be correct. What I wanted to say is that while Rigol's ADC obviously is ASIC as a type of product because it is custom made IC that was made by company for their specific use, ASICs are usually made for a very specific function: a switching matrix for a high speed interconnect, a complete integrated sound engine for a synthesizer, or something like that.
In this case, Rigol made "just another ADC", a chip for which there is alternative. Of course that assessment is based on my limited knowledge from what Rigol has published. Maybe they did combine ADC and some sort of DSP to linearize response or something like that.. In which case it would be really single use application specific chip for scopes that could not be replaced easily. And would allow them to have simpler BOM and maybe make significant saving in FPGA resources and such...

But from what I see they still have same architecture as before with ADC-FPGA-App processor. So it seems any saving would be just in price of chip. I personally think it is more about control of sourcing the chip than good price (which is just a bonus).

You are welcome!!

The ADC, or FPGA, is likely the single most expensive IC component in the DSO, and at this price point every $ in BOM matters. Without a custom in-house ADC, one is restricted to available chips from AD, TI and maybe some others, and don't think that anyone can get these ADCs at a price that would fit this price point.

We must remember that TI, AD and others have developed and produced high end performing ADC chips that satisfy many market segments, these incurred much higher development costs, and likely occupy more precious silicon area, involve extensive testing and so on. Whereas Rigol was able to isolate the important parameters that are more meaningful to the DSO market, trim the architecture to reduce the up front development costs, reduce the Si area, and so on.

Would wager that if we got ahold of one of these ADCs where we could do detailed isolated standalone chip testing, the overall performance would be mediocre in general compared to TI and AD. Things like no missing codes, monotonicity, differential & integral linearity, ENOB, aging, drift, temp, PSRR, and so on would not compare well with the TI and AD counterparts. Many of these parameters aren't that important in a DSO application, I mean who really cares if the ADC has a stuck lower bit, or non-monotonic around the LSBs, and so on. Now consider using this ADC as feedback in a complex high speed control system, stuck bits and non-monotonic behavior would be a disaster indeed!!

I strongly doubt that. For use in a DSO you need a very good ADC as well. Maybe even more so compared to a control system. Otherwise you'll get all kinds of weird distortions that will show up in a signal. In a control system you can work around it through signal processing (calibration) but when visualising a signal (either time or frequency domain), it is likely that faults do show up and there is very little you can do to cover things up.

I don't know what Rigol has done to get their 'own' ADCs. It could even be that they are buying dies from TI or AD and put these into their own packages with an easier to route pin order. Or maybe they wanted some pre-processing or an interface that allows for a lower BOM cost at the FPGA side. If you look at the ADCs from TI, you'll see that these typically have a JESD204B interface. This uses several high speed, differential pairs to transport the data. At the FPGA side you'll need expensive transceivers. Looking at Dave's teardown, it seems that the ADC Rigol uses has a parallel style interface. Likely a DDR style interface using the standard SERDES inside the FPGA I/O blocks which is a much lower cost solution IF you can place the FPGA close to the ADC.

[2N3055]

Yeah, I have no idea what Dave did there... It is obvious that scopes are not set the same... Which is not surprise because Rigol decided to implement "FFT dummy mode" transformation with no control of FFT parameters. I keep repeating that you need to either implement full RT Spectrum analyser (that does ALL of the necessary transformations from FFT to spectrum display) or a proper FFT mode where you have control over mathematical FFT parameters.

Hmm. That sounds quite different than your outburst half an hour earlier:

Are you really that thick or you are paid to spew bullshit?
What is wrong with that FFT? It is slower because device has slower CPU. That is not a bug.
A 8 bit converter dynamic range is bug??

Muppet.

Did you actually watch Dave's video before you lashed out at Fungus? Care for an apology?

And speaking of Rigol's "FFT dummy mode": Maybe Siglent's "FFT expert mode" is not all that great, if Dave supposedly can't use it properly?

I appreciate your T&M expertise and the fact that you share it freely on this forum. But your continuous undercurrent of Siglent vs. Rigol bias does taint its value.

I apologize to you if I offended you in any form. It was not my intention. As for Fungus, I got fed up with his general hysteric cheerleading  without substance, based on few videos without independent confirmations.. And thank you for both honest and candid critique and kind words.

As for me advocating Siglent vs Rigol, I said it many times. I like Siglent's new touch scope line and platform and decisions behind it.
As for Rigol I said (repetitively):
- kudos to them for developing a 2nd generation of ASICS for scopes.
- this second gen front end and ADC chips seem to perform very well, and are great improvement. Again kudos.
- they are bringing to market 12 bit scopes with good analog performance to low cost market. That is great news for everybody-
- they took large undertaking to create new touch scope platform. It looks pretty good so far, it is still early to say how far the development will go but so far impressive effort. Again congrats and bringing that kind of platform into low end is also very good news... While it is in early stages of development I have no doubt it will mature with time. Now they have modern platform in a game. Absolutely great.

Rigol fanboys se my comments as an attack. Which is a myopic and wrong way to look at things. If I were to really work against I would be really quiet and let Rigol keep making half made product and scratch their head "what could we do to make it better".
I don't attack product. I'm not only pointing something is wrong, I always say what is wrong AND what needs to be fixed.
The way I see it Rigol gets free consulting and fanboys get a glimpse there are better things than just worshiping status quo...

If my comments are really not welcome and not useful to anybody I can stop wasting my time and just keep commenting on Siglent scopes. They seem to really appreciate constructive comments and listen, so my effort is not wasted with them.

[tautech]

...........
- they are bringing to market 12 bit scopes with good analog performance to low cost market.

Are you sure ?
Go back a few pages and look at the disturbing display from a Bodnar pulser where fast edge artifacts seem to be hidden.

[2N3055]

Where is the size setting ?

One less parameter to juggle. 

What really counts is the resolution.

Every time I start to feel bad that I said something bad to you, you keep doubling down on wrong stuff..

If you don't understand why it is necessary to have control over number of bins, that is proof you need to learn a bit more before you are qualified to discuss quality of FFT implementation.

To make it clear, there is nothing wrong if scope has auto set of number of bins. It can really be nice for some quick look-see. But it has to have manual control too. If you are doing anything that you have to compare two results you need to be able to make parameters same between two measurements otherwise you cannot compare them 1 to 1.

[Warhawk]

Guys, to be more constructive in comparing your DSOs - let you design a measurement, which may show some tangible data when running on the DSOs of your choice. .....

It is me thinking aloud again. For what I do, I would like to see a comparison of e.g. Keysight, R&S, Rigol and Siglent for:

• the switch node of a flyback converter
• i2c or SPI communication, showing the frames, triggering on a specific character, etc.
• output ripple of a DC-DC converter
• fast PWM, RMS, 10-90 rise times, etc. ...

Feel free to inspire me with other examples.

I think, these are kind of measurements that the target audience (hobbyists) does. If you do something more advanced, you simply need a better scope. I have access to high-end scopes but I've been using RTB2004 for practically everything last couple years**. I also have a second scope 54815A 54825A with 2.5 GHz active probes in case I needed something "fast".

I also wonder why some of you are so obsessed with FFT. What is it good for (in this category)? Many old scopes have it too. Practically useless. At least to what I've seen. You need it often? Get a spectrum analyzer! You need it once a year? Dump the data and use Octave.

Just use what was delivered in the package and do some useful measurements. I want to know if I could somehow rely on what Rigol shows. If so, I am ready to try it (DHO900 because of Bode).

my $0.02, again, just me thinking aloud. Feel free to throw rocks at me :-)

**it is portable, stays at my desk, it has quirks too

Note: Dave reviewed a product from Siglent some years ago. He complained about the chassis, rust and sharp edges. Yesterday, I nearly cut my finger when uphacking my 54815A. Edges around the fan are annoyingly sharp.

[nctnico]

Looks nicer..

Which ones are missing?

Wait until you have it in your own hands. 
Before one example:
Where is the size setting ?

You can probably force the FFT length by setting the memory length. Assuming Rigol follows the generic FFT implementation, then the number of bins is FFT length / 2.

I also wonder why some of you are so obsessed with FFT. What is it good for (in this category)? Many old scopes have it too. Practically useless. At least to what I've seen.

For low frequency stuff FFT can be quite usefull to get an idea where noise is coming from. A spectrum analyser doesn't work well at 50Hz or even less. A good FFT implementation on a DSO will. But it does take a bit more effort to set it up properly and I'm not sure whether having spectrum analyser-ish controls on a DSO are actually helping. Recently I used FFT on a DSO to figure out where LF noise was coming from by inspecting the frequency spectrum of the signal.

[2N3055]

...........
- they are bringing to market 12 bit scopes with good analog performance to low cost market.

Are you sure ?
Go back a few pages and look at the disturbing display from a Bodnar pulser where fast edge artifacts seem to be hidden.

So far it looks decent enough. You must take into account price.. 800 is cheaper than many funny Owons...
It is fab for the price.. And give Rigol some credit, they are not Muppets.. You and I both like "Siglent's way" better, but Rigol is not some third rate no name company.

As for pulse response, I'm waiting for Martin to get his.
Then I will help him with testing protocol, and we will know what real performance is.
What I see as biggest problem is not the actual analog part. It's analysis, measurements, etc... Useful segmented mode is completely missing as far I can see, measurements graphic representation is step back (you could see more measurements on screen at the same time with stats on DS1000Z) etc... But since all available videos are about irrelevant stuff but not these things, I cannot say if that is really so or we just don't know. Maybe it is missing but will be added later ? Which also reinforces fact that Rigol released unfinished platform. Which is also not such a sin, because even R&S did that... It is just that users need to know that and consent to buying a house that is only partially finished, but it is Ok because they got really good price because of it..

[ebastler]

...........
- they are bringing to market 12 bit scopes with good analog performance to low cost market.

Are you sure ?
Go back a few pages and look at the disturbing display from a Bodnar pulser where fast edge artifacts seem to be hidden.

That's assuming that what the Siglent scope shows is the ground truth. In Dave's quick test and comparison, the R&S RTB2004 showed the same pulse shape as the two Rigols -- https://www.youtube.com/watch?v=S8jrpCoZyx8&t=1937s. Do you have more data to confirm that the Siglent gets it right?

[Warhawk]

For low frequency stuff FFT can be quite usefull to get an idea where noise is coming from. A spectrum analyser doesn't work well at 50Hz or even less. A good FFT implementation on a DSO will. But it does take a bit more effort ....

Thank you, yes, this makes sense.