EEVBlog #1119 - Designing a 1kV Isolated Oscilloscope

[EEVblog]

Bart Schroder from Cleverscope talks about the challenges in designing the world's highest performance isolated oscilloscope.

Measurement demo on a 500V MOSFET H-Bridge and how to accurately probe it. Then a teardown and walk through of the design of the new CS448 1kV 4CH 200MHz 14bit isolated oscilloscope and the custom probes, power supplies and optical fibre interfaces they had to design to get this performance.

https://cleverscope.com/products/CS448

[T3sl4co1l]

I don't have much to say about this.

Very impressive.

I'm sold.

Tim

[EEVblog]

I don't have much to say about this.
Very impressive.
I'm sold.

It's hard to watch this and not get sold.

[EEVblog]

Bart has written are article on the development that is going to be published (maybe) in Silicon Chip, he let me upload it here:
http://www.eevblog.com/files/CleverscopeSep2018.pdf

[Andrew McNamara]

I remember an article on a high voltage DC interconnect in South America in one of the electronics magazines (probably Silicon Chip) long ago. One of the photos showed a oscilloscope attached to a stack of laser-triggered thyristors - the scope was well back in the HV cage, with glass rods from all the controls extending outside the cage.

[BrianHG]

If I ever end up designing my professional grid tied exercise bike, I will buy 2 of these...

I'm not sue, but, I hope I can sync up 2 of them, though, it wont need perfect synchronized timing between the 2 units, just the the 2 are both onscreen at 1 time and bot have timestamped logging.

[EEVblog]

I'm not sue, but, I hope I can sync up 2 of them, though, it wont need perfect synchronized timing between the 2 units, just the the 2 are both onscreen at 1 time and bot have timestamped logging.

It has a sync connector on the back.

[Brumby]

So ... it has everything including the kitchen sync.

Very nice bit of kit.  (So is the price tag  ).

[Phoenix]

Nice! See if my work is interested in buying one... it's about time someone made something better than the Tektronix TPS2000! The TPS has done me well in the passed for probing floating gates, but never that kind of dV/dt.

[LapTop006]

Bart has written are article on the development that is going to be published (maybe) in Silicon Chip, he let me upload it here:
http://www.eevblog.com/files/CleverscopeSep2018.pdf

Huh, I thought in your video he said the scope did send clock out to each ADC, but in the article he says otherwise? Perhaps that was a late design change.

Edit: Indeed, it was changed, later in the article it goes in to that. Serves me right for commenting without finishing the whole article.

I was at Electronex while you were filming this, looked like a good chat.

[BravoV]

Curious about the custom isolated transformer, made a discussion thread about it -> HERE.

[Hydron]

Thanks Dave, very good video (on both interviewer and interviewee sides). I'm glad to see this out there, Bart is a good bloke (and an influence for me becoming an EE) and I hope the product does well in the niche he's aimed for.

I certainly have run into some of the issues this scope tries to solve (scoping gate drive nodes switching >300V in <10ns) and would loved to have been able to confidently say what the dip at the miller plateau was (I could probe well enough to tell it was there, but not how bad it was, other than the magic smoke remained contained). Will see if I can play with a loan unit when I'm in NZ during the summer.

[JPortici]

I have no words.
Bravo.

[oPossum]

Very impressive.  The price is very reasonable for such a capable unique instrument.

[mikeselectricstuff]

I think there would be scope to solve this problem much more cheaply :
Eliminate the probe issues by having a small adc+frontend unit that is placed close to the signal.
Battery power to eliminate the supply issue.
Transmit data over fibre, maybe use off-the-shelf SFP fibre-ethernet modules.

Wouldn't have quite the performance or flexibility, but could be way cheaper for those that don't need quite that level of performance.   

[BartSchroder]

Hi Brian,
Yes 2-4 units can be synched with a shared clock and trigger. We use a short HDMI cable plugged into the Trigger Out on one box to Trigger In on the other box. The sampling clock is synchronous across all units.

The PC application allows up to 4 connected units, but it's getting pretty busy, and you need a fast PC !
cheers,
Bart

[mikeselectricstuff]

Of course there;s this approach, but no channel-channel isolation...

[Hydron]

I think there would be scope to solve this problem much more cheaply :
Eliminate the probe issues by having a small adc+frontend unit that is placed close to the signal.
Battery power to eliminate the supply issue.
Transmit data over fibre, maybe use off-the-shelf SFP fibre-ethernet modules.

Wouldn't have quite the performance or flexibility, but could be way cheaper for those that don't need quite that level of performance.

I have done something similar with an entire scope (one of the ethernet connected older generation cleverscopes, briefly shown in the video) and a wifi ethernet extender, both battery powered. Allowed me to look at two signals with a common reference floating _way_ above ground (several hundred kV at ~70kHz), but was really a special purpose setup rather than a day-to-day usable one, though I guess I could do the same to look at a single gate voltage (or gate drive plus source referenced drain voltage).

That isolated scope controls pic is fantastic btw!

[T3sl4co1l]

I think there would be scope to solve this problem much more cheaply :
Eliminate the probe issues by having a small adc+frontend unit that is placed close to the signal.
Battery power to eliminate the supply issue.
Transmit data over fibre, maybe use off-the-shelf SFP fibre-ethernet modules.

Wouldn't have quite the performance or flexibility, but could be way cheaper for those that don't need quite that level of performance.

I think this is what the Tek probes do (plus a few more fibers for signals and power), and I'd like to do something like that myself some day; but hell, if their probes are working that well, despite the 1/4 wave stub that is the cable plus isolated module hanging off the switch node, I can't very well beat that.

Tim

[voltsandjolts]

Wow, nice engineering...and explained very openly by such a nice chap.
Thank you.

[Hydron]

I think there would be scope to solve this problem much more cheaply :
Eliminate the probe issues by having a small adc+frontend unit that is placed close to the signal.
Battery power to eliminate the supply issue.
Transmit data over fibre, maybe use off-the-shelf SFP fibre-ethernet modules.

Wouldn't have quite the performance or flexibility, but could be way cheaper for those that don't need quite that level of performance.

I think this is what the Tek probes do (plus a few more fibers for signals and power), and I'd like to do something like that myself some day; but hell, if their probes are working that well, despite the 1/4 wave stub that is the cable plus isolated module hanging off the switch node, I can't very well beat that.

Tim

I believe that the Tek probes use power over fibre, plus an electro-optical modulator for getting the signal across the barrier and some other low-freq stuff to get decent DC performance (there is a thread somewhere on the forum about it, and Tek's white paper here: https://www.tek.com/document/whitepaper/tektronix-isovu-measurement-system-white-paper ). Completely different and very interesting technology with it's own benefits and drawbacks (e.g. higher bandwidth available, huge sticker shock).

As for doing it on the cheap, I'm not sure whether it makes sense - sure you could compromise performance and convenience (batteries would be a pain) and do it a bit cheaper, but the question is whether the target market would value cost over performance? I don't see something like this being able to be built down to a hobbyist level cost easily - those scopes tend to use shared ADC ICs and count the cost of every extra component (and independent isolated front ends is a lot of extra parts!).

[Dubbie]

This was such a great interview. Excellent interviewee, intelligent questions and great video quality(for a trade show) You’ve had some really good videos lately Dave. Keep ‘em coming!

[bitwelder]

This was such a great interview. Excellent interviewee, intelligent questions and great video quality(for a trade show) You’ve had some really good videos lately Dave. Keep ‘em coming!

I don't have remotely the needs for such a scope, but I enjoyed a lot the video. Thumbs up to Dave, hoping we can see more of such interesting interviews on the channel, and also big thanks to Bart for talking about the development of their scope.

[nctnico]

I didn't watch all of the video but got the technical part. I fully agree that the biggest challenge of doing an isolated channel (on any piece of equipment) is getting rid of the common mode current from the power supply and capacitive coupling in general. From there it is smooth sailing.

[Ranayna]

These fibre links remind me of something i read about a couple of years ago. Intel developed something very similar to what is used here. Maybe it is the same thing?

It was supposed to be used for high speed internal busses in servers and workstations. After those one or two articles i read, i never heard anything about it again. Seems to have found a use