EEVBlog #1119 - Designing a 1kV Isolated Oscilloscope - Page 1
Forum section: electronics / general

author: EEVblog
author_rank: Unknown
timestamp: September 06, 2018, 10:08:44 pm
content: 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

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 06, 2018, 11:19:18 pm
content: I don't have much to say about this.Very impressive.I'm sold.Tim

author: EEVblog
author_rank: Unknown
timestamp: September 06, 2018, 11:34:59 pm
content: Quote from: T3sl4co1l on September 06, 2018, 11:19:18 pmIt's hard to watch this and not get sold.

author: EEVblog
author_rank: Unknown
timestamp: September 07, 2018, 02:28:49 am
content: 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

author: Andrew McNamara
author_rank: Regular Contributor
timestamp: September 07, 2018, 02:45:38 am
content: 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.

author: BrianHG
author_rank: Super Contributor
timestamp: September 07, 2018, 04:07:40 am
content: 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.

author: EEVblog
author_rank: Unknown
timestamp: September 07, 2018, 04:21:51 am
content: Quote from: BrianHG on September 07, 2018, 04:07:40 amIt has a sync connector on the back.

author: Brumby
author_rank: Unknown
timestamp: September 07, 2018, 04:59:44 am
content: So ... it has everything including the kitchen sync.Very nice bit of kit. (So is the price tag).

author: Phoenix
author_rank: Frequent Contributor
timestamp: September 07, 2018, 05:07:34 am
content: 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.

author: LapTop006
author_rank: Unknown
timestamp: September 07, 2018, 05:17:22 am
content: Quote from: EEVblog on September 07, 2018, 02:28:49 amHuh, 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.

author: BravoV
author_rank: Super Contributor
timestamp: September 07, 2018, 05:18:31 am
content: Curious about the custom isolated transformer, made a discussion thread about it ->HERE.

author: Hydron
author_rank: Super Contributor
timestamp: September 07, 2018, 10:19:13 am
content: 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.

author: JPortici
author_rank: Super Contributor
timestamp: September 07, 2018, 11:10:36 am
content: I have no words.Bravo.

author: oPossum
author_rank: Super Contributor
timestamp: September 07, 2018, 11:31:21 am
content: Very impressive. The price is very reasonable for such a capable unique instrument.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 07, 2018, 11:51:13 am
content: 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.

author: BartSchroder
author_rank: Newbie
timestamp: September 07, 2018, 12:14:44 pm
content: 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

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: September 07, 2018, 12:37:58 pm
content: Of course there;s this approach, but no channel-channel isolation...

author: Hydron
author_rank: Super Contributor
timestamp: September 07, 2018, 12:55:15 pm
content: Quote from: mikeselectricstuff on September 07, 2018, 11:51:13 amI 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!

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 07, 2018, 04:26:46 pm
content: Quote from: mikeselectricstuff on September 07, 2018, 11:51:13 amI 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

author: voltsandjolts
author_rank: Unknown
timestamp: September 07, 2018, 09:20:19 pm
content: Wow, nice engineering...and explained very openly by such a nice chap.Thank you.

author: Hydron
author_rank: Super Contributor
timestamp: September 07, 2018, 09:48:54 pm
content: Quote from: T3sl4co1l on September 07, 2018, 04:26:46 pmI 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!).

author: Dubbie
author_rank: Unknown
timestamp: September 08, 2018, 10:20:44 am
content: 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!

author: bitwelder
author_rank: Super Contributor
timestamp: September 08, 2018, 12:57:05 pm
content: Quote from: Dubbie on September 08, 2018, 10:20:44 amI 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.

author: nctnico
author_rank: Super Contributor
timestamp: September 08, 2018, 04:13:03 pm
content: 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.

author: Ranayna
author_rank: Super Contributor
timestamp: September 08, 2018, 06:35:39 pm
content: 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

author: NiHaoMike
author_rank: Super Contributor
timestamp: September 08, 2018, 09:06:49 pm
content: I'm surprised it's not Thunderbolt, which would handle the bandwidth easily.

author: BrianHG
author_rank: Super Contributor
timestamp: September 08, 2018, 09:37:42 pm
content: The 1Gbit might be a bandwidth limitation of the Altera Aria LVDS channels as well as memory bandwidth. They might be using only 2-4 pairs LVDS feeding a network PHY. This wouldn't have been an issue with a Stratix, but, I suspect putting in an 4-8k$ FPGA would double the price of the scope.

author: nctnico
author_rank: Super Contributor
timestamp: September 08, 2018, 11:18:20 pm
content: Quote from: BrianHG on September 08, 2018, 09:37:42 pmWouldn't the FPGA have an internal gigabit transceiver which can drive the SFP port (network) directly? A Xilinx Spartan6 which costs a few tens of dollars has no problem with that.

author: BrianHG
author_rank: Super Contributor
timestamp: September 08, 2018, 11:59:25 pm
content: Quote from: nctnico on September 08, 2018, 11:18:20 pmYes, and they are using a 2 pair gigabit transceivers for the gigabit Ethernet/optical networking.They didn't want to go further than that.They are using the ' 5AGXBA1D4F31C5N ', a 260$ fpga in lots of 27.It has 6.5536 Gbps transceivers, not the 10.3125 Gbps or 12.5 Gbps required for a 10Gbit lan connection.The DDR3 ram controller works at 533Mhz or 667Mhz depending on configuration and wiring.They also started development around 3 years ago, so, back then, there were no Aria FPGA in the series which had the 10Gbps and were also affordable. Like it or not, we are stuck with 1Gbps lan and would need to wait for the next version of the scope for the 10Gbps lan support.I'm not sure but the speed and width of the ram and simultaneous sampling with network transfer may also be a factor. I only saw 4 ram chips on the PCB, however, pausing the sampling during the network transfer would make things faster. They would need 40 gigabit per second transfer rate for real time transfer of all 4 channels at full sampling speed.Since they have full firmware update-ability, they wont be using Altera's cheap quick-asic mask version.

author: schmitt trigger
author_rank: Super Contributor
timestamp: September 09, 2018, 12:19:47 am
content: This chap Bart comes across not only as a very talented individual, but also as a down to earth, almost folksy individual.His enthusiasm is contagious.In my book, a great man.Don’t have a need for such high performance instruments in the foreseeable future, but I hope all of his efforts are successful. In economic terms.

author: GigaJoe
author_rank: Frequent Contributor
timestamp: September 09, 2018, 03:30:34 am
content: Transfer 40Gb data in overall a humangous job calculation, using a standard IP stack ... and entirely inefficient; Ideally something like infiniband interface more suitable , so it would be a separate board with ram storage then PC will have access to this storage and manipulate with a data. That alone would be approx $1500 to $4500 - depend on ram capacity ... BUT possible to connect a multiple scopes .... is any one need 16 channels ?, consider of synchronization can be done over infinband as well

author: LapTop006
author_rank: Unknown
timestamp: September 09, 2018, 04:51:31 am
content: Quote from: Ranayna on September 08, 2018, 06:35:39 pmI guess you're thinking of what becameIntel Omni-Pathwhich is only really interesting for the supercomputing folk, haven't heard from my friends in that space what they think.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: September 09, 2018, 12:16:43 pm
content: Dave, that's sellingI wonder what part numbers are used for the fiber isolation?

author: mjs
author_rank: Regular Contributor
timestamp: September 11, 2018, 11:28:11 am
content: The fiber link looks like muRata MMC3. There's not too much data available about it, though. Its main market is apparently in active optical cables.https://www.murata.com/about/newsroom/techmag/metamorphosis20/productsmarket/module

author: nctnico
author_rank: Super Contributor
timestamp: September 11, 2018, 06:37:45 pm
content: Quote from: GigaJoe on September 09, 2018, 03:30:34 amProducts like that already exist. I've worked on such a project/product for one of my customers: a multi-channel distributed data acquisition system for use in high voltage testing labs (this needed slightly more than 1kV isolation...). Synchronisation is done using White Rabbit sub-nanosecond time synchronisation developed by CERN (which they use to synchronise data acquisition in the LHC). It is pretty cool to sample the same signal using two seperate acquisition units and have the resulting waveforms overlap flawlessly.

author: rrinker
author_rank: Super Contributor
timestamp: September 11, 2018, 07:29:00 pm
content: Quote from: schmitt trigger on September 09, 2018, 12:19:47 amTotally agree. That was a great interview, and a very clever bit of design. Too bad I have no use for something like that, because he sure as heck sold me.

author: lordvader88
author_rank: Frequent Contributor
timestamp: September 21, 2018, 05:51:24 pm
content: I u took a conductor, and energized it with +500V, then -500V, at whatever freq like in the motor, with the 10ns rise time....why can't they just build a probe and probe the EM waves just above it in free space ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 21, 2018, 06:15:22 pm
content: An e-field probe works just fine for high frequencies... however, can you calibrate it accurately, given that the probe can be any distance above any charged shape?And it doesn't do anything for differential sensing, of course.Tim

author: lordvader88
author_rank: Frequent Contributor
timestamp: September 21, 2018, 06:23:10 pm
content: wouldn't "they" do a bunch of number crunching on whatever some probe detects, in order to isolate the signal they are after ? , like in any number of branches of scienceI have no idea what it would cost anyways, the scope in the video is like +10,000