EEVblog #675 - How To Reverse Engineer A Rigol DS1054Z

[Dave Turner]

Dave - your tip regarding probing a board with a voltage less than 'say' 0.5V seems fine for silicon based junctions and is much appreciated.

I recall a time that when germanium transistors were prevalent. If I remember correctly the forward voltage was approx 0.2v. I still have a couple of OC71s which surprisingly survived after an unavoidable 99% clear out a couple of years ago. Now I'm so far out of the loop that I don't know whether germanium transistors/junctions are still used or not.

I have a dim recollection of a 1960's project for a "buzz out" detector that ran at a potential difference below that of the germanium forward voltage.

Does anyone recall it and/or would such a device have any value in todays' age?
 

[Rasz]

Would be really nice if someone reverse engineered this (or one with similar performance) frontend properly, and released it as open hardware. I would gladly buy a module with 2 inputs at ~$50.

What features and performance would you expect from something like this?

Would you want everything up to the ADC or the ADC as well?  In this particular design the integrated ADC handles most of the gain switching so the front end is simplified.

hmm you are right, I forgot HMCAD1511 is ~$80 in single quantities. That puts my idea out of its misery

The way I see it, this rigol can be broken down like this
$100 frontend (4 inputs, adc)
$100 computing (data processing, application processor)
$100 case, supply, screen, keyboard, pcb
$100 software


I was thinking of a building block if someone wanted to experiment/play with/build oscilloscope. Every other piece of the puzzle is available off the shelf, except for a good quality, properly designed and battle tested frontend. Some uni or a MOOC could even do a course on building measurement equipment using module like this and fpga dev board. Currently closest thing I can think of is
-analog discovery, 5MHz analog BW $100-300
-embeddedartists labtool, 3-12MHz analog BW ~$200
-Red Pitaya, 50MHz analog BW, but only 120MHz sampling, $470
-maybe Smartscope? same as red pitaya, but not shipping and most likely not open if/when it ships

ps: forgot one
-BeScope, claimed ?50MHz analog BW, 250MHz sampling, $50, but not a proper frontend

[Alex Eisenhut]

Wow, my DS5102C feels kind of pokey now.

[David Hess]

hmm you are right, I forgot HMCAD1511 is ~$80 in single quantities. That puts my idea out of its misery

$100 frontend (4 inputs, adc)

Rigol saved a lot by using 4 inexpensive signal conditioning front ends to drive a single 4 channel ADC which does almost all of the gain switching.

I was thinking of a building block if someone wanted to experiment/play with/build oscilloscope. Every other piece of the puzzle is available off the shelf, except for a good quality, properly designed and battle tested frontend. Some uni or a MOOC could even do a course on building measurement equipment using module like this and fpga dev board. Currently closest thing I can think of is

... examples ...

The ones I have seen struck me as fragile and low performance.

I would want 1 Mohm inputs with overload protection, fast overload recovery which places some limits on the topology, and thermal balancing to prevent long settling times.  The Rigol design discussed here has all or most of that and like Dave says, it is recognizably similar to analog and DSO front ends going back decades so there is a lot of existing documentation about how to do it.

Making a universal design work with different ADCs which may or may not have programmable gain would be difficult.  Calibration of the transient response and input compensation would be a problem.

[krivx]

Dave - your tip regarding probing a board with a voltage less than 'say' 0.5V seems fine for silicon based junctions and is much appreciated.

I recall a time that when germanium transistors were prevalent. If I remember correctly the forward voltage was approx 0.2v. I still have a couple of OC71s which surprisingly survived after an unavoidable 99% clear out a couple of years ago. Now I'm so far out of the loop that I don't know whether germanium transistors/junctions are still used or not.

I have a dim recollection of a 1960's project for a "buzz out" detector that ran at a potential difference below that of the germanium forward voltage.

Does anyone recall it and/or would such a device have any value in todays' age?
 

FYI OC71s are quite sought after by people building clones of 1960s guitar effects pedals. You might make some money selling them.

[ohmineer]

Nice video, it would be nice to see this kind of exercise with other boards you have.
Thanks for your effort.

[Fungus]

The way I see it, this rigol can be broken down like this
$100 frontend (4 inputs, adc)
$100 computing (data processing, application processor)
$100 case, supply, screen, keyboard, pcb
$100 software

Nothing for R&D and the distributors ... ?

[SNGLinks]

Dave - your tip regarding probing a board with a voltage less than 'say' 0.5V seems fine for silicon based junctions and is much appreciated.

I recall a time that when germanium transistors were prevalent. If I remember correctly the forward voltage was approx 0.2v. I still have a couple of OC71s which surprisingly survived after an unavoidable 99% clear out a couple of years ago. Now I'm so far out of the loop that I don't know whether germanium transistors/junctions are still used or not.

I have a dim recollection of a 1960's project for a "buzz out" detector that ran at a potential difference below that of the germanium forward voltage.

Does anyone recall it and/or would such a device have any value in todays' age?
 

FYI OC71s are quite sought after by people building clones of 1960s guitar effects pedals. You might make some money selling them.

Perhaps I should sell mine on eBay - my user name is OC71 ?

[Gunb]

Hi Dave,

great blog again. Thank you for that.


Kind regards
Gunb

[Yansi]

Hi Dave, really thank you for your video about Rigol RE!

I am working on some sort of educational project now - I learn how to use CPLDs/FPGAs, so I decided to try to make a simple oscilloscope. I have got some MAX1422 ADCs laying around (20Msps 12bit) - I'd like to use them. But there is a catch - my experience and knowledge of analog design is poor. (Well... thats relative, but designing a (at least) working AFE is not so easy.) Your video helped me a lot, to get some ideas how to do this. I'd like to avoid any costly specialized ICs.
Yesterday, I was investigating your schematic and also found the two wrong NPNs in the diff amp. Does anybody know, how it might be really connected? 
Did you measure the supply voltage, to these stages? I tried to get some estimates of the bias currents in the stages. Is it standard +-5V? It looks like that might be less there...
Someone in this thread just said, that the diff amp right input might be for setting Vcom for the ADC - I also thought about that. It has to be - I do not see any other way in the circuit, how to control the common voltage for ADC.
Is there a possibility, to make a simple discrete front end also with gain selection? (There would be no need for big bandwidth, just maximaly a few megs, maybe tens with MAX1420..) I'd like to discuss that, maybe I start a thread about it. I'd like to make this as an opensource project for those interested in 

[_Wim_]

Excellent video. Made me join this forum immediatly! (first post here)

[mullecy]

Excellent video. Made me join this forum immediately too!  (first post here, although I've been following on youtube for years)

I was actually simulating the rigol 1052E from A. Helene schamatics to see how it works when this video was published and I have lots of informations and questions on those oscilloscope analog front ends.

My method for reverse engineering:
Basically the same: taking good pictures of both sides, but I don't print on transparent sheets:
I just use GIMP(free photo software) and its multilayers functions.
This way I can dynamically change the transparency and add my own layers with annotations, draw mark pins that I've
already checked (so I don't do things twice)...

http://www.eevblog.com/files/Rigol-DS1054Z-Schematic-FrontEnd.pdf

Here's my analysis: (correct me if i'm wrong)

• The jfet section
  It's not really an amplifier but a follower/buffer that helps dealing with the very high impedance of the source signal (909kOhms).
  The lower part of the jfet seems to be a basic current source to maintain a steady offset between the input and the output of the jfet and the transistor.
  The two 249R from 1052E are gone in 1054Z, but they were useless to my opinion and were just limiting the range of possible outputs (or maybe this was a protection or a way to tweak the bandwidth).
  
• The OA section
  It's just assuring that the output follows the DC offset of the input.
  But what is bothering me is why did they add that ?   
  Dave says that's because the jfet part can't do the DC amplification. Well I don't agree because the jfet part does it (it's not really amplification just a follower with impedance improvement)
  I just don't understand why they added such a complex setting, because using the OA is quite complex because you have to deal with the transition (amplitude and phase) from AO response in very low frequencies and capacitor in front of the jfet for high frequencies. (see http://rigol.codenaschen.de/images/thumb/0/0c/DS1052E_HW58_PCB_Schematics_-_Ch1_analog_front-end.jpg/800px-DS1052E_HW58_PCB_Schematics_-_Ch1_analog_front-end.jpg for a schematic for 1052E)
  
• The differential section
  Nothing really to add to the discussion: there's something wrong with the top transistors. With what Draw only 0 or 1(with a big enough offset in inputs) can be active and this is not what a differential amplifier should do (unless you want some sort of comparator maybe)
  The biggest problem I see is the lack of variable gain amplifier before the ADC. Maybe they just use the internal ADC amplifiers to do that.
  Using formulas from Horowitz book: http://en.wikipedia.org/wiki/The_Art_of_Electronics
  Common Mode Gain: Gm=-Rc/(2.R1+Re)=-82/(2.BigCS+50)=near 0 (the current source impedance is very high)
  Differential Gain: Gdiff=Rc/2(re+Re)=-82/2(52.5)=-0.78 (if we say for example current source gives 10ma then re=2.5Ohms (25/I in ma))
  

[uwezi]

Here's my analysis: (correct me if i'm wrong)

• The differential section
  Nothing really to add to the discussion: there's something wrong with the top transistors. With what Draw only 0 or 1(with a big enough offset in inputs) can be active and this is not what a differential amplifier should do (unless you want some sort of comparator maybe)
  The biggest problem I see is the lack of variable gain amplifier before the ADC. Maybe they just use the internal ADC amplifiers to do that.
  Using formulas from Horowitz book: http://en.wikipedia.org/wiki/The_Art_of_Electronics
  Common Mode Gain: Gm=-Rc/(2.R1+Re)=-82/(2.BigCS+50)=near 0 (the current source impedance is very high)
  Differential Gain: Gdiff=Rc/2(re+Re)=-82/2(52.5)=-0.78 (if we say for example current source gives 10ma then re=2.5Ohms (25/I in ma))
  

After looking at the latest teardown video I also got interested in the discrete differential amplifier section - and yes, something must be wrong in the DaveCad^TM drawing.

Looking at the hires images from the actual teardown of the DS1054Z I noticed that there is an additional pair of MMBT3904s on the other side of the circuit board in the front-end section, which are missing from the RE drawing... but I am still trying to figure out what's going on there...

[t_i_t_o]

So if ALL FOUR of those filter caps are disconnected does that make room for a secret 200mhz model? 


After all, so far we only have 3 different 1000z models(50,70,100) and there are 4 possible combinations of the filters...hmmm.  Although I guess it would be just as possible to have a 25mhz model as the 4th combination of filters.

I was very curious about the upper question too... until now!

Yesterday I received my new lovely DS1054Z. Before unlocking all its features I decided to tear it apart and measure which bandwidth selection capacitor is enabled and when. Generally speaking I could switch among three bandwidths - 20MHz, 50MHz and 100MHz after unlocking, so the stats are:
20MHz - one capacitor enabled
50MHz - the other capacitor enabled
100MHz - no capacitors enabled!

So unfortunately there is no hidden bandwidth...

[Fungus]

So unfortunately there is no hidden bandwidth...

There's no more unlocking but it's usually about 130Mhz if you measure it very carefully.