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Old 25th May 2002, 12:04 AM   #21
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I don't know about the guy from Germany but I tried Wima caps in crossover and they sounded better than Solen...I guess it all depends on taste.

As you know Digi-Key doesn't carry HFQ caps anymore and the only stock I have is 120u and 1000u. I settled on the latter.
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Old 25th May 2002, 12:58 AM   #22
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Default "Goudreau triplet",

Quote:
Originally posted by HarryHaller
I urge everyone to read this link and try the decoupling stratagy outlined by Pete Goudreau. The guy is super sharp and a have a paper he wrote on digtal decoupling that is one one my references on the subject.
Harry,

I have almost all of Pete Goudreau's posts concerning his struggle against TCP Dacs and UJB. I regularly reread them, and every time I'm amazed by his knowledge and physical background.

Do you know where I can find the paper you mention ? Is it available somewhere ?

Quote:
While the regulators are important, the bypass caps are doing all the work above a few hundred KHz
The OSCON caps are great for electrolytics with COG ceramic bypass caps for the real high frequency stuff. We are talking currents in 10s of MHz here and a film cap is not going to cut it.
I used the "triplets" with more than benefit long ago on my "old" Dac, but without a multiple regulator approach. But concerning your OSCON/COG duet, I'm a little bit confused : COG SMT chips usually don't range over 1nF, and they become bulky as the value increase, as does their ESL. Do ultra low inductance 0612 chips exist in COG diel ? Is the OSCON good inough to avoid the "100-200 nF range" cap for intermediate frequencies bypassing ?

Moreover it seems to me that particular 'lytics and ceramic chips are to be chosen for their optimum combination of ESL/ESR and resulting impedance curve. Do you have some typical values in mind ?
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Old 25th May 2002, 01:34 AM   #23
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Default Pete Goudreau

I worked at Alcatel and knew Pete from a mutual friend. The paper is proprietary to Alcatel. Howard Johnsons book has a great chapter on decoupling caps and there is probably some stuff
on his website www.sigcon.com. I will look on the web for some app note locations. Electrolytic, stacked film and Surface Mount ceramic is probably the way to go.

http://www.faradnet.com/

http://www.sanyo.com/industrial/comp...scon_home.html

http://www.sigcon.com/Jennifer/Pubs/...ductbypass.htm

http://www.sigcon.com/news/2_1.htm

http://www.sigcon.com/Jennifer/Pubs/news/5_3.htm

http://www.sigcon.com/Jennifer/Pubs/news/2_3.htm

H.H.
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Old 25th May 2002, 10:22 AM   #24
dorkus is offline dorkus  United States
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where can you buy OSCON caps in the states? do they compare favorably to Panasonic FC?
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Old 25th May 2002, 05:42 PM   #25
tiroth is offline tiroth  United States
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I have a question about the "Goudreau triplet". Does (physcially) stacking the bypass caps really have a significant advantage, other than being a clever way to retrofit an existing design? It seems to me that loop size is the same whether stacked or on the board, because vertical distance from ground matters too.
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Old 25th May 2002, 08:05 PM   #26
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Default Bypass caps for digital circuits

Mount the caps as close to the supply pins as possible. The small ceramics closest to the part.

http://www.sigcon.com./articles/straight/bypass.htm

http://www.glencoe.com/ps/ee/williamson/decoupling.html

H.H.
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Old 26th May 2002, 06:11 PM   #27
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Ultra low inductance SMT chips use 0612 packaging, which basically are of the same dimensions than their 1206 counterpart, but with the long side metallized. This allows to reduce the intrinsic inductance of the chip (400pH or less). It's then quite difficult to parallel several of them without adding pcb traces, and the only solution is stacking. A mere 100 mils trace can add up to 1 nH to the total inductance, and can destroy your efforts to lower this inductance...
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Old 26th May 2002, 10:04 PM   #28
BrianL is offline BrianL  United States
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Default 0612 vs 1206 SMT caps

I find it hard to believe that using 0612 caps for bypassing the
digital parts something like a CD player would have any
advantage over something like 1206 caps. The inductance
is only reduced slightly. Placement and dielectric type are
much more important. You can get 10nF (aka 0.01uF) C0G
caps in 1210 package and these should be just fine. I've
got some on my desk at work but haven't gotten around to
trying them yet.

And if you think this is just too much inductance, go for 0805
caps, though I doubt you'lll get more than 1nF in C0G dielectric.
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Old 26th May 2002, 11:32 PM   #29
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Default 0612 vs 1206 SMT caps

I agree. The main point is to keep traces to caps short and fat to minimize parasistic inductance. I have used copper foil on top or the digital IC for this and and works great. You can get this tape from DigiKey. I believe it is made by 3M.

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Old 27th May 2002, 01:32 AM   #30
BrianL is offline BrianL  United States
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Oh, and I forgot to mention:

The ICs' lead frames and bond wires (i.e., the "pin" of the
IC and the stuff that connects it to the actual "chip" inside)
are far longer than the difference between the lengths
of 0612 and 1206 capacitors. This is true even for suface
mount ICs -- at least until we get to ones that are mere solder
bumps on the surface of the "chip" itself. (and when we're
at that point, we might as well forget about DIY with the
stuff)

The pins, lead frames and bond wires have far more inductance
than an extra 0.006" in choosing a 1206 cap over an 0612 cap.

Yes, the various copper foil tapes are made by 3M ("Scotch"
tape... ) and maybe others. And I do believe they're available
from Digi-Key.
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