At least you actually do something, not like a good many here that would like to make people think otherwise.
I spend more time at actually experimenting with what works the best instead of fighting with PC software that only gets it close but not good enough.
I just love those that talk shit and most likely hardly even touch a piece of equipment. When they do I am sure they're all thumbs and fingers with it and most likely end up getting some one else to do it for them and take all the credit for it.
Those guilty of this need not to step forward, I already know who most of you are.
I had a guy tell me a cheap scope (he always buys the most expensive equipment) I got for him was broken-- turns out the brightness control (or whatever you call it on a digital scope) was turned down. Same guy claimed an expensive SRS bridge with 0.1% accuracy was giving 10% error on a reading-- turned out he was using 100Hz to measure a tens-of-pF cap and it was performing well within spec according to the manual. He has written peer-reviewed papers on these things.. sad.
It's a rare person that can get all the theory right and the practice right- they deserve to be well-rewarded.
Best regards, Spehro Pefhany
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How deep does your understanding go? Quantum mechanics? String theory? Do you do closed-form Maxwell's Equations on every circuit? Or full EM simulation? I bet you don't.
I'm not bragging. I wish I had the tools to fully understand or simulate everything we do, down to the physics. Sometimes you do whatever works.
"That they need to." Yes. Understanding *everything* about an IC would be great, but we're not privvy to that information.
The pragamatism issue is real, and there are serious risks from not fully understanding a system. But there we are, working with what we have.
I can't see a lot of risk in designing a transmission-line transformer by experiment. It should be very reproducible, and it is. A little math can check for things like breakdown voltage, if that matters.
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
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"John Larkin" wrote in message news: snipped-for-privacy@4ax.com...
As a physicist, I can affirm that. Others may vary.
Doesn't count -- even the string theorists don't understand the stuff. ;-)
And you don't?
I do on every single board I make. Not closed-form, but open-form approximation, qualitative accuracy. Implemented in wetware, too. Works very well.
Well, if you really wished, you'd buy the entire Ansoft suite and *do* it -- but I'm guessing that wish isn't as unconditional as it was phrased. In actuality, you don't care at all, and are more than happy enough guessing. Which again illustrates your inconsistent self-representation.
Are you aware that ~20nH is ~86mm of 50 ohm, 0.67c coax?
Assuming the headers pictured are 0.1" centers, the cores are roughly T37 size ferrites, a bit thicker than usual. I get 14mm for the length of a single turn on a regular T37, so it might be closer to 18mm per turn, maybe 20mm with coax thickness. That's 60mm total length, or 14nH. The soldered connections and board traces have almost as much, depending on if there's a ground plane just out of sight or not. But by then it's not mutual, which is all the more reason it's not LL you're supposing about.
Actual performance will show helical resonator action starting around
1GHz, which is what the under-hump on your leading edge comes from. And probably other nasties if you tested it with a ps generator rather than the "sub-ns" this particular device produces.
Tim
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I learned a little in chemistry classes... very little.
My understanding is not that they don't understand it, it just doesn't predict anything different from existing quantum theory.
Have you solved the Schrödinger wave equation for any of your systems. Only then will I call you a real engineer ;)
Hey, want to help me design a LF shielded loop antenna from coax? It sounds like it would be right down your alley! I don't know nothing about birthin' no babies, Ms. Scarlett! But it looks like I'm going to have to learn...
Use Maxwell's equations? No, I don't. And I rarely do EM sims; I did post about one such, here a while back, using ATLC2 to design a PCB stackup for an edge-launch SMA connector. It was tedious, and it worked. It was sort of cool...
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"Qualitative accuracy?" What does that mean?
I use a couple of PC apps to calculate trace impedances, Appcad and TXLine. But you don't have to understand a lot to drive those.
It's a matter of cost, learning curve, and need. So far, the tools that I've mentioned, and a few home-made programs, do what we need.
I don't guess about things that matter... see above. But I don't think there's anything wrong with designing a gate driver/mosfet/transmission line transformer circuit using instinct and experiment. The edges I'm getting are about 20x faster than the numbers on the mosfet data sheet. So much for theory.
If I need a pullup resistor or a bypass cap value, or a trace width for small DC currents, I usually guess.
I calculate 6 nH/inch, pretty close.
What I'm really aware of is that it works and we sell lots of them.
That particular transformer in the photo was driven by a gaasfet. It worked fine, made really pretty isolated pulse outputs, about 500 ps edges. About 2000 of those transformers trigger most all the various gadgets at NIF.
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John Larkin Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
Jamie's confidence is touching. In fact what he is saying is that he is envies people who have better luck when they fight with the PC software, and wants to think that they are less fortunate at the bench. It's a slightly corrosive point of view, and may make him a difficult colleague.
It does happen, but not very often. Most people with enough sense to get a PC to do what they want it to have enough sense to also make a soldering iron do what they want it to.
He's made up whatever it is he uses instead of a mind.
It's just a few pF. The winding is just a few inches long.
The 2000 outputs are separate triggers, "clients" (things that we trigger) scattered all over the site. The isolation is only to break ground loops and keep jitter down.
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(one of my very few published papers)
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John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Of course not. It slows things down, even when it's possible. And besides, I like to solder once in a while.
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation
Of course. But it's capacitance across a galvanic isolation barrier, and - as such - injects AC current into the isolated ground. If your clients aren't keeping track of that, they aren't doing their job right.
155.52-MHz seems surprisingly low. I would have thought that there were faster standard frequencies that they might have adopted, with correspondingly lower edge jitter. And it's not "your" paper - you aren't first author, and clearly didn't write it.
It may be one of the few published papers that list you as an author, which is no small thing, but it's not "your" paper.
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