[SI-LIST] Re: Capacitors arrays. worth it or not?
- From: "Hill, John" <jhill@xxxxxxxxxx>
- To: <Mark.Randol@xxxxxxxxxx>, "si-list" <si-list@xxxxxxxxxxxxx>
- Date: Mon, 22 May 2006 13:50:22 -0400
Mark,=20
We have uploaded an application note from American Technical Ceramics
concerning placing capacitors vertical and horizontal. The URL is:
http://si-list.org/files/tech_files/ATC%20select_cap_wireless.pdf
I have also sent an e-mail to the application engineer about the issue
of eddy currents limiting the field. The data in the application note
does not look like it supports the idea and I do not understand the
physics.=20
John
=20
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-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Mark Randol
Sent: Monday, May 22, 2006 10:33 AM
To: si-list
Subject: [SI-LIST] Re: Capacitors arrays. worth it or not?
> -----Original Message-----
> From: si-list-bounce@xxxxxxxxxxxxx=3D20
> [mailto:si-list-bounce@xxxxxxxxxxxxx] On Behalf Of Jerry Martinson
>=3D20
> I've always wondered how discrete cap performance is affected=3D20
> if the caps plates are parallel with the underlying plane or=3D20
> if they are perpendicular. I'd think that having them rolled=3D20
> 90 degrees
> (perpendicular) might make them perform better in some=3D20
> regions. I wonder how this would extend to arrays and=3D20
> whether arrays are configured rolled or not. Does anyone=3D20
> know? =3D20
American Technical Ceramics (ATC) used to recommend 'vertical' placement
of their porcelain caps for just this reason. I've seen it make several
100MHz's of difference in the measured resonance frequency. That was on
a relatively thick 2 layer PCB, so on a board with a thinner component
to ground layer spacing this could be more significant <guess>. I
didn't find it on their web site, but here is their link.
http://www.atceramics.com/
Now how much of this was due to plate coupling to the substrate, or
reduced effective capacitance and inductance because of current crowding
towards the new 'bottom' of all the plates, beats me. It seems to me in
the horizontal orientation, the upper plates would have slightly more
inductance due to the greater loop area. Which effect dominates,
capacitance or inductance? =3D20
The problem at the time was fixed, so we didn't investigate further.
--
Mark Randol, RF Evaluation & Application Engineer
Not speaking for my company, etc
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