DIY Source Meter Unit - initial thoughts

RE: DIY Source Meter Unit - initial thoughts

dustooff — Sun, 06 Sep 2020 06:01:22 GMT

Hi Jan,

I also have an interest in SMU's for various test purposes, have been collecting ideas for a few months now, just recently found that the sigrok people have introduced smuview.

https://www.eevblog.com/forum/projects/smuview-a-sigrok-gui-for-power-supplies-multimeters-and-more/

https://github.com/knarfS/smuview/releases https://sigrok.org/wiki/SmuView

I know some of us want stand alone smu system, but if it were as modular as practical, we assemble a system tailored to individual needs. I have tested the ADALM1000 with PixelPulse2, but am still interested in the potential of sigrok integration.

RE: DIY Source Meter Unit - initial thoughts

jc2048 — Sun, 07 Jun 2020 18:36:31 GMT

Some more 'for information' or 'add to the reading list' stuff.

This is the Wikipedia page for SMU

https://en.wikipedia.org/wiki/Source_measure_unit

it includes a link to an issue of the HP Journal devoted to the HP4145A Semiconductor Parameter Analyser. First article looks at the capabilities of the instrument, so good if you're trying to sort out your own spec. The second article includes a block diagram (simplified) of an SMU and lots of interesting stuff on the design side of it.

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1982-10.pdf

On a different tack, this is an interesting take on the Howland.

http://www.ti.com/lit/pdf/slyy054

RE: DIY Source Meter Unit - initial thoughts

shabaz — Sun, 07 Jun 2020 18:13:28 GMT

Hi Jan,

There's a couple of open source SMU-like devices that might be worth exploring, in case it gives some ideas for your project.

One is ADALM1000 ADALM1000 see here for more info Getting Started with the Active Learning Module ADALM1000 it has limits of 5V and 200mA, so that is quite restrictive. It cannot handle negative voltages, although there is an on-board 2.5V output which could be used instead of ground for some measurements.

It is only £25+tax, so well worth it just to experiment with.

Also, there's some benefits maybe to using the same protocol/API for your project or extending it. When I wrote up about it, people just (I'm sad to say) whinged about the software because they couldn't install it on Linux without making some effort, but nowadays there's Windows software for it too. The open source software is called PixelPulse2, maybe it could be adapted to suit your SMU design, to save some effort. I don't know if you intend on-board LCD, or attaching to a PC. The same interface protocol is used by a software suite called ALICE which provides additional functionality although then it not really functioning as an SMU but as other instruments, like impedance meter, logger, etc.

There's a more advanced model called ADALM2000, but that's unfortunately ten times the price, but looks impressive (again within its limits) - just too much beyond my budget for experimentation though, although I think it is still value-for-money as a lab-in-a-box.. I just wish it was lower cost. It's a much more complex design than ADALM1000 though.. uses an FPGA, and I think USB 3.0..since it supports 100Msps. The ADALM1000 has a limit of (I believe) 100ksps.

RE: DIY Source Meter Unit - initial thoughts

genebren — Sun, 07 Jun 2020 17:16:12 GMT

I was thinking of separate modules for driving current and voltage, though I can see how they might be combined

This is an interesting idea. Going a little bit further, it might me nice if the voltage/current source could be modular enough that you might be able to a high and low current version. In addition it might be nice if you could have the option to have single and dual channel versions. I was really interested in the Keithley SMU that was roadtested until I realized that a single channel unit could not be used for testing DC-DC converters, which would be handy. Just blue sky thinking at this point as this is a large undertaking and the last thing you need at the start is a lot of feature creeping.

Nice to have so many experts and extremely thorough thinkers in one room!

RE: DIY Source Meter Unit - initial thoughts

jc2048 — Sat, 06 Jun 2020 19:55:32 GMT

This is interesting. Several times when I was doing the transistor blogs I wondered about about doing some kind of modular test setup [though it was fun designing the ad-hoc circuits and wiring the prototype boards each time]. I couldn't make up my mind whether separate boxes for each function would be best or some kind of mainframe with plug-in boards.

It shows how ignorant of test and measurement I am that I didn't even know that SMUs were a thing, though I had come across curve tracers and was vaguely conscious of automated testers with 'pin drivers' and all that. I obviously don't move in the right circles.

I was thinking of separate modules for driving current and voltage, though I can see how they might be combined [though, if you do, it kind of then starts to move towards what Michael is doing with his impedance analyser - I'd worry then that the spec is going to run away faster than you can chase after it]. I also toyed with the idea of using an isolated serial communication bus between modules [maybe something like a fast MIDI, or differential like DMX], to save the cost of working with ethernet [I'd have had some kind of a hub, with a small SBC, to relay stuff back to a laptop].

One complication for me, with the MOSFET tests, was the necessity for doing quick tests because of the effect of temperature from the dissipation. That then moves you away from DMM type techniques for the measurement to something that works sample and hold, with the timing and synchronisation issues that introduces [as far as I can see, SCPI won't be very good at synchronising and sequencing things at speed]. Although you might think that temperature effects would only be important for power devices, I was seeing such effects at much more modest levels with very small packages like SOT-23 and smaller.

Anyway, it will be interesting to see what you come up with.

One request: please don't put it all in one blog. That programmable load blog with 16 pages of comments is getting impossible to trawl through.

RE: DIY Source Meter Unit - initial thoughts

fmilburn — Sat, 06 Jun 2020 16:50:22 GMT

I would like to contribute. If I can keep up with you guys.

RE: DIY Source Meter Unit - initial thoughts

genebren — Sat, 06 Jun 2020 16:26:23 GMT

Jan,

Let me know if you need any help. My strengths would be in the area of controllers/converters and human/digital interfaces.

Gene

RE: DIY Source Meter Unit - initial thoughts

michaelkellett — Sat, 06 Jun 2020 12:04:17 GMT

If you like to use it my power amplifier as blogged about in: Frequency Response Analyser Progress

would be a possibility for your driver section.

I'll have some boards soon (Fedex say Monday) and some test results soon after.

Perhaps we could swap some parts.

(Or you are welcome to use any parts of the design that you fancy.)