I show my work: circuits, breadboards, PCBs, waveforms, products. You don't have anything to show.
JT does show some stuff he did 30 or 40 years ago. Anything current, he just brags about how great it is without further detail.
Very few people here actually show their products, or even hint at what they are.
-- 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
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1 copperelds back
Looking at the artwork, what I would up with was the inductor wiring on top, a full plane on layer 3, and the current-carrying connection (previously on layer 1) moved to layer 4. It might be possible to do better, but this was more than good enough.
Prior to this, the voltage induced across the nearby 8mm main ground (source for the entire system) was quite impressive. Magnetism works.
On reflection, it might actually be possible to do a GND pour around the pads and wire them on lower layers. Hmmm.
Sure would be easier not to have to do that though...this board would need a total re-do.
-- Cheers, James Arthur
wasn't.
investigation
the
copper
back
Yes. And route the power traces such as to minimize loop area.
I have to worry about 60 Hz B-field hum pickup in some of my gear. Fractions of a microvolt will be noticed. It's rackmounted next to who knows what other gear or fans. Loop area of critical stuff has to be minimized, or loops planned to cancel.
Having 60 Hz sidebands in an NMR spectrum is like a famous restaurant having roaches in the salad.
-- 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
some
a square
-- Truish, but since the capacitance will be very small because of the miniscule electrostatic coupling between the affected surface areas of the turns interacting with the ground plane, I think it's more likely that the varying magnetic field cutting the plane will result in what's giving you heartburn. --- >The noise that I'm seeing is mostly below 10 MHz. The wavelength at 10 MHz is 30 >meters. The metal box here is about 5x4x1". A 10 MHz EM wave couldn't propagate >inside that box.
[snip]
you're
Larkin providing a perfect description of himself ?? ...Jim Thompson
-- | James E.Thompson | mens | | Analog Innovations | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at
-- Thank you.
you're
-- You got it!
you're
Funny! I was thinking of having a salad for lunch... I think I still will ;-) ...Jim Thompson
--
| James E.Thompson | mens |
| Analog Innovations | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona 85048 Skype: Contacts Only | |
| Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
| E-mail Icon at http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
copper
back
So, you have those out there too?
Jamie
copper
back
I've never seen a roach here in SF. I think the climate doesn't agree with them. They were everywhere in New Orleans, bug ugly flying ones. Yuk.
We rarely see mosquitoes here either, just a few days in late summer maybe.
-- 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
some
a square
make a
ground
of the
the
higher
highest
The difference between a hack and an engineer if the willingness to test their hypotheses. Particularly when it is reasonably easy.
?-)
square
the
highest
No, the difference is that an engineer is quantitative and a hack is not.
-- 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
induced
grounded SMB
high
currents.
Big B fields from the shoot through. Mostly harmonics in the first place, do an fft if you can't just grok it.
?-)
some
a square
make a
ground
d of the
the
er
highest
Not necessarily. You look very like a hacker, but have been known to measure stuff, though you don't always understand what you are measuring.
-- Bill Sloman, Sydney
Umm. I don't think so. The 21st or harmonic was killing the 10.7 Mhz IF thus wiping out the whole band.
?-)
as
RF.
some
voltage
sitting
By the way JL, what are the trace lengths between the switches and the inductor, also the bypass caps? How big are the loops?
?-)
SMB
A B field has a vector direction. So if it is magnetic pickup, I could rotate the scope ground loop and null the induced voltage, right?
-- 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
About as close as they can be. The input and output rails are both big copper planes. The trace from the switcher to the inductor is 200 mils total run, and all that does is add a few nH in series with the 4.7 uH inductor. The switcher is on the opposite end of the board from the output amps, and dipole fields fall off with, I recall, the cube of distance.
I can sense a magnetic field with a multiturn probe coil only very close to the inductors, and it looks like a square wave at the switching frequency. That's not what the EMI looks like at the arb outputs.
-- 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
fall
I think induced circulating groundplane currents fall off much more slowly?
What about putting the inductor on the end of 12 inches of coax or twisted pair, as a test? Does that work?
the
-- John Devereux
and
switcher
fall
I wish I had a sheet resistor field solver. Problems like this keep coming up.
If I pick two points on a sheet of copperclad 0.75" apart and inject 1 amp, the voltage drop near those points is about 100 uV. An inch away, the voltage drop across a similarly spaced pair of points is about 5 uV. At 2.5 inches away, I can't really measure it but it looks to be around 0.5 uV. It's dropping fast.
Of course, that's DC.
I don't have any teledeltos paper! Can you still get that stuff?
Too much work! I'm 99.9% sure it wouldn't make any difference. There are a couple of more promising things to try, but the only way I'm going to get 40 dB or so improvement is to spin the layout and use different switchers.
-- 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
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