Author Topic: The Rigol DS1052E  (Read 284609 times)

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Offline EEVblog

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Re: The Rigol DS1052E
« Reply #165 on: February 14, 2010, 09:32:11 AM »
This looks super exciting Ross, you may have cracked it!
Please detail your mod as soon as you are able.
Also, what does it look like with a square wave and a normal clip probe? The overshoot and undershoot is an easy way to see how the high frequency response has improved.

Dave.

Offline EEVblog

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Re: The Rigol DS1052E
« Reply #166 on: February 14, 2010, 09:36:19 AM »
Rigol makes some 300 MHz scopes too.  What if the analog front end on the 100 MHz scope is bandwidth limited also, and we've got filters on both models with different values?  What if our *real* bandwidth can be even higher than 100 MHz?


Phil Allison has measured the usable bandwidth here:
http://groups.google.com.au/group/aus.electronics/browse_frm/thread/8db8df6c7f9f710/6edf366688b538db?lnk=gst&q=rigol+phil#6edf366688b538db
400MHz for a visible and viewable waveform!
So there could certainly be much more to this front end than meets the eye.

Dave.

Offline xani

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Re: The Rigol DS1052E
« Reply #167 on: February 14, 2010, 11:49:10 AM »
If that was true, Rigol scope is probably best deal in history, 200Mhz (assumming 5 probes per cycle) for $400, insane...

Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #168 on: February 14, 2010, 05:53:53 PM »
I wonder if I could have permission to use someone's photographs of the analog input section?  My digital camera got smashed up the last time I flew and I haven't replaced the LCD yet.

I checked out a function generator from school, I wish I had checked out some 100 MHz scope probes too!  It turns out that this is crucial too.. I should have known, the 50 MHz probes that come with it have their dB plots in the documentation.

EDIT:  FLAWED MEASUREMENT
Here is what a 1 MHz square wave looks like.  There are 150 MHz transients in channel two that don't show up in channel one.
« Last Edit: February 17, 2010, 02:02:49 PM by rossmoffett »
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Offline EEVblog

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Re: The Rigol DS1052E
« Reply #169 on: February 14, 2010, 06:52:27 PM »
Feel free to use my internal pics.
When testing with a signal generator it's best to use a good coax instead of the probe.

Dave.

Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #170 on: February 14, 2010, 11:46:35 PM »
Dave, I know I'm supposed to use BNC connectors, it's just that I don't have them.  ;D This is actually my first oscilloscope so I just have the out-of-box parts and whatever I can check out from school.

I'll do a full how-to when this is peer reviewed, I think, but here's what I found.

At first I thought it would be trivial, it was pretty clear that this was a Butterworth filter from the frequency vs. voltage plots that have been posted, so there should be some row of inductors and capacitors.  I found one, but it was a filter for the AD8370 power.  I figured that out by tracing it to the pin and then checking the datasheet.  Then as I read the datasheet (should have thought of this FIRST) I ran into something interesting.  In the app notes they specifically mention using this as a variable gain amplifier for low-resolution AD converters.. like an 8 bit AD converter.  This is on page 19 of 28, and right at the top of the page is a Butterworth filter with a Cauer topology.  This is in case the AD converter can't handle high frequencies.. or in case you want to use the same design for two differently priced oscilloscopes. :D  NO WONDER the part is rubbed out!

VHI is pin 8 and VLO is pin 9, this is the amplified output signal. There are two gold pads on the PCB that are labelled as test points on the DS1102E.  I noticed attenuation here.  Then, looking through the comments on Dave's teardown blog I saw that someone guessed the part number for the smaller, 8-pin part.  It wasn't the right part number, but it fit the bill exactly (this is not an Analog Devices part, though, because it matches none of their ADC drivers, not a TI part either).  The only thing that was off was that the VHI and VLO pins were reversed, so I just assume this is the AD converter buffer.  The datasheet reference circuit for the AD9288-40 ADC uses an AD8138.  This doesn't come in a TSSOP-8 package.  In fact, I can't find any op-amp with that configuration in a TSSOP-8 from Analog Devices.

Looking at the board, I noticed that the signal split in two directions at the test point.  One way went to the buffer and the other went through a capacitor..





Re-organize a bit, and it's clear that there is a high-pass filter straight between signal HI and signal LO.  This is why some of my measurements were out of phase, even though both channels were measuring the same signal.
(values based on in-circuit measurements by a cheap LC meter, not in stone)



The via hanging off of the inductor has a direct path to the shift register, I'm not sure why.  It's not grounded, and I don't know why it would be tied to a logic high anywhere, not sure what's going on.  There's a via hanging off of the inductor at the top too, I couldn't find where it goes.

So my "hack" was just to remove the capacitor on the VoutHI pin.  I just now took all of the measurements as I was making the drawings, and I took out the other cap on the VoutLO pin.  There doesn't seem to be any additional change, I believe that the AD8370 output is isolated from ground, which means when you sever just one capacitor the whole filter is rendered ineffective.  So all that has to be done is cut the path to the filter somehow.  I removed a capacitor with my soldering iron, you could also just slice the trace (but that's a little dirty).

In closing, your mileage may vary, at your own risk, warranty void and null, etc etc.

Here are some more good pictures, showing how the FFT smooths out with a mod and how a square wave shapes up.  Flip between them quickly and the difference is very noticeable.  Again, channel 1 (yellow) is unmodified, channel 2 (blue) has the filter removed.
« Last Edit: February 15, 2010, 10:21:34 AM by rossmoffett »
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Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #171 on: February 15, 2010, 11:08:26 AM »
If anyone else is willing to try this, I suggest you just pop up one end of the capacitor on pin 8 of the variable gain amplifier (the one right below the topmost round golden test pad).  This will allow you to easily undo the mod later if you wish, and if you're a skilled SMD solder wiz.

I'd love to see what the results are with better lab equipment, is anyone gonna give it a go?
« Last Edit: February 15, 2010, 11:14:34 AM by rossmoffett »
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Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #172 on: February 15, 2010, 01:21:48 PM »
I did the best I could, used a "BNC to alligator clips" cable and split the output from my high frequency function generator to both channels with short wires.  The stability and accuracy appears MUCH better than when I was using probes, so I charted the unmodified output vs. the modified output.  The voltage gain in the modified channel is very apparent.

I used equivalent time sampling with normal acquisition until I was down to about 10 MHz, then the generator was too unstable and I had to time-average it.

Comparing it to luky315's measured frequency response, it looks like I have over 100 MHz bandwidth now!
« Last Edit: February 15, 2010, 05:01:39 PM by rossmoffett »
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Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #173 on: February 15, 2010, 05:31:20 PM »
I'm not sure what's going on here, Channel 1 seems to be picking up the transients now.  Maybe I had a poor connection when I took the earlier measurement.
« Last Edit: February 15, 2010, 05:33:56 PM by rossmoffett »
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Online flolic

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Re: The Rigol DS1052E
« Reply #174 on: February 15, 2010, 06:35:05 PM »

I'd love to see what the results are with better lab equipment, is anyone gonna give it a go?

Yes, I modified second channel on my 1102E last night. I removed both (HI & LO) caps, btw. they are 160pF on my scope. I don't have any function/signal generator that go beyond 100MHz range, so I used old FM tuner and pick up signal from local oscillator set up at 125MHz.

It seems that mod did not do anything to my scope, signal amplitude on modified channel is just marginally better than unmodified. I used standard probes. Today I will buy some BNC connectors and coax and make high bandwidth 50 ohm terminated probe.

But I noticed another thing when measuring complex signal (square wave, 32MHz xtal osc. and 200kHz osc. with joined outputs). On modified channel you can clearly see higher components of a signal, in a 250MHz range! So it seems that mod is actually working  ;)
Just hope that that is real signal and not some kind of aliasing or ringing... ;D

Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #175 on: February 15, 2010, 07:19:45 PM »
Those are in-circuit measurements - I just measured the caps (I kept them) out of circuit and mine are ~160 pF too.  Doh!  There must be something else around to limit bandwidth.. unless you have different size inductors, or maybe there is something behind those vias.

That ADC driver could be a bandwidth limiter, if I could find a match for it.  It's not an 8-lead TSSOP as I posted earlier, I looked closer in zoom images and it seems to be a 10 pin no-lead chip of some sort.  It's so hard to tell, they're tiny!  I still can't find it from Analog Devices, though it must be one of theirs based on the Analog sandwich around it.  I imagine it's classified as a differential op-amp, but I can't find it in that category yet.  It's approximately 2.6 x 2.9 mm (+/- .1 mm) based on the photographs, I found that by comparing to known parts data.

Don't worry about re-installing the filter - if you read the datasheet on the page that I mentioned it notes that the filter is only necessary depending on application.  At least, I think.  The only use those capacitors could have is to hold a voltage stable, but I don't see how that could be necessary.

Given that you have a 100 MHz scope, you should only see marginal improvements at 125 MHz.  There will be a sharp dropoff following that, though.  If you have anything that will generate 100 MHz, check to see what V1/V2 is there.  It should be .7 if channel 2 is of a sufficiently higher bandwidth, as you can see where I posted V1/V2 at 50 MHz.  From my graphs above, you can also see that my good luck starts to end at about 130 MHz.  That's where the modified channel gain starts losing ground to the unmodified channel.  In the app notes for the ADC there's nothing else stopping the signal but the ADC driver, so that may be the next place to look, unless someone finds some filter before the variable gain amplifier.
« Last Edit: February 15, 2010, 07:47:19 PM by rossmoffett »
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Online jahonen

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Re: The Rigol DS1052E
« Reply #176 on: February 15, 2010, 08:51:19 PM »
I'm not sure what's going on here, Channel 1 seems to be picking up the transients now.  Maybe I had a poor connection when I took the earlier measurement.


That looks like spurious oscillation. For easy bandwidth check, a high-edge rate digital (repetition frequency can be set to very low frequency, say, 1 kHz) signal is a easy check. One should see rise or fall time of about 0.35/BW if everything is ok. For 100 MHz that translates to 3.5 ns etc. If the rise time is not reduced, then the effective bandwidth for practical measurements is not going to be very significant.

You can get fast edges from just about any digital chip, except from that old 4000-series CMOS. Even old PIC16F877 seems to have about 160 MHz bandwidth (without any other additional loading than scope probe), see here. That contains some probing hints also :)

Regards,
Janne

Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #177 on: February 15, 2010, 09:10:49 PM »
I understand spurious oscillation, it's just that the earlier post I made was observing a 1 MHz square wave under identical conditions and the unmodified channel failed to pick up all of the intricacies.  I believe I must have not grounded the probe properly the first time around.  Thanks, though!

OK, I think I have narrowed down what kind of chip the ADC driver is.  I thought I saw an extra pad on one of Dave's close-ups, which would have explained why I couldn't find an 8-lead package, but upon close inspection from top views I can't see that it would be the case.  Browsing the ADC drivers at the Analog Devices website seemed futile, until I checked a supplier.  These chips are available in packages not described on the AD website.  I noticed that the screen print around the part seems to be 3x3 mm.  This leads me to believe they must have some oddball part, but the PCB still looks like it would fit these two parts, which come with the squared edges.

http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=AD8350ARMZ20-ND
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=AD8132ARMZ-ND

They are 900 MHz and 350 MHz respectively.  I'll have to crack it open again and take some measurements on gain and voltage to be sure which part it is, still could be any of the other 8 pin parts.  The version with the worst (feasible) bandwidth is the AD8137, with a bandwidth of 110 MHz.  The only lower ones clock at 38 and 30 MHz.  I can find it in a package with bevelled edges in 3x3 mm, but not with the square ones.

and.. here's the AD8138 in the package that's in the scope:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=AD8138ARMZ-ND

A 320 MHz part.
« Last Edit: February 17, 2010, 01:50:06 AM by rossmoffett »
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Offline rossmoffett

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Re: The Rigol DS1052E
« Reply #178 on: February 17, 2010, 09:25:15 PM »
Yes, I modified second channel on my 1102E last night. I removed both (HI & LO) caps, btw. they are 160pF on my scope. I don't have any function/signal generator that go beyond 100MHz range, so I used old FM tuner and pick up signal from local oscillator set up at 125MHz.

It seems that mod did not do anything to my scope, signal amplitude on modified channel is just marginally better than unmodified. I used standard probes. Today I will buy some BNC connectors and coax and make high bandwidth 50 ohm terminated probe.

But I noticed another thing when measuring complex signal (square wave, 32MHz xtal osc. and 200kHz osc. with joined outputs). On modified channel you can clearly see higher components of a signal, in a 250MHz range! So it seems that mod is actually working  ;)
Just hope that that is real signal and not some kind of aliasing or ringing... ;D

I took mine apart again in light of your not noticing much difference.  My digital camera still has a broken screen but I used it to take some pictures anyway, they're of pretty low quality or I'd post them.  I made a quick-flash gif between my scope and yours, I can't find a single component difference!  Those inductors hanging off of the caps that we removed are different values on Dave's scope, but not on mine.

I flipped to the underside, flabbergasted, and realized that those vias drop down to a couple more caps on the underside!  In addition to those, there are two other sets near the signal input jack and the input of the variable gain amplifier.

So I think I might still have found it, those caps on the underside might be the key difference.  There may even be additional filtering on the input side of the variable gain amplifier too.  My curve seems to lack that dramatic filter swoop, seems a little too linear.  I don't know what the underside of the DS1102E looks like though, so I can't say for sure.  All I know is that it seems like my scope is working fantastic with this mod, I wish I had another reference to compare to besides my unmodded channel.  The DS1102C scopes at school are only 400 MS/s with no sinx/x feature, so they aren't good for comparison.  Unfortunately all of our other 100 MHz scopes are analog and long separated from their last cal date.

Shine a light underneath the board and you will see everywhere that signal passes down.  They cut out chunks of the inside layers around those areas.
« Last Edit: February 17, 2010, 09:34:13 PM by rossmoffett »
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Online flolic

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Re: The Rigol DS1052E
« Reply #179 on: February 17, 2010, 09:52:23 PM »
Ok, I modified both channels. I don't know if that was wise idea but it's over now  ;D
Few thoughts:
-First, original probe (for 1102E) is declared as 150MHz bandwidth and WILL attenuate higher freq. signals.
-Second, my modified scope (with homemade high bandwidth probe) easily picked up 446MHz PMR radio transmission from few meters away. It is easily seen on FFT display. Unmodified scope can show that transmission only if I put radio right next to the probe.

From that it is obvious that mod is working. But I am still worried about spurious/false readings...
« Last Edit: February 17, 2010, 11:37:17 PM by flolic »


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