[SI-LIST] Re: Low-Q Controlled-ESR Bypass Capacitors
- From: "Hill, John" <jhill@xxxxxxxxxx>
- To: <istvan.novak@xxxxxxxxxxx>, <Istvan.Novak@xxxxxxx>
- Date: Fri, 26 May 2006 09:41:42 -0400
Istvan,
If the capacitor vendors will not make the low Q capacitors that we
need, then we will just have to find a different solution. The PCB
materials are wonderfully lossy at high frequencies and should make fine
capacitors. All we need to do is use the FARADFLEX Material from
Oak-Mitsui to increase the capacitance per square inch of PCB.=20
With a board size of 50 square inches here are the capacitance values
they say can be achieved:
=20
ZBC2000 16 nF
ZBC1000 32 nF
BC24 40 nF
BC16 64 nF
BC12 76 nF
BC8 124 nF
BC12TM 180 nF
BC16T 440 nF
Here is link to their web site:
http://www.oakmitsui.com/pages/advancedTechnology/faradFlex.asp
If there are any capacitor vendors out there please let me know why I
should buy high Q capacitors that will resonate with the PCB and each
other. These High Q resonances will make for EMC problems, but we can
fix the problem by not buying high Q capacitors.=20
Best regards,
John
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx]
On Behalf Of Hill, John
Sent: Thursday, May 25, 2006 11:17 AM
To: istvan.novak@xxxxxxxxxxx; Istvan.Novak@xxxxxxx
Cc: si-list
Subject: [SI-LIST] Low-Q Controlled-ESR Bypass Capacitors
Istvan,
I have just finished reading your paper: "Overview of Some Options to
Create Low-Q Controlled-ESR Bypass Capacitors". I think it is a good
idea. But I read in your paper: "as of today no commercially available
such component exists"
That was back in 2004. Can we buy then yet?
Best regards,
John
-----Original Message-----
From: istvan.novak@xxxxxxxxxxx [mailto:istvan.novak@xxxxxxxxxxx]=3D20
Sent: Wednesday, May 24, 2006 9:30 PM
To: Hill, John; Istvan.Novak@xxxxxxx
Cc: steve weir; Larry Smith; Mark.Randol@xxxxxxxxxx; si-list
Subject: Re: [SI-LIST] Re: Capacitors arrays. worth it or not?
John,
Yes, you are correct, what determines the series resonance frequency is
the capacitance and the total loop inductance of the mounted part, the
body inductance will be part of it.
There are the following clarifications. I would not use the length of
an 0508 capacitor body to estimate the quarter-wave resonance. As larry
pointed out it is better to use the height of the part, which is about
30-50 mils for a typical 0508 capacitor. Also, because the vertical
transmission line is loaded with the many capacitor plates, we end up
with a heavily loaded transmission line, where the approximate time of
flight is tpd~sqrt(LC) where L is the vertical inductance and C is the
total capacitance.
Regards,
Istvan Novak
SUN Microsystems
From: "Hill, John" <jhill@xxxxxxxxxx>
Date: Wed May 24 16:58:36 CDT 2006
To: Istvan.Novak@xxxxxxx
Cc: steve weir <weirsi@xxxxxxxxxx>, Larry Smith =
<LSMITH@xxxxxxxxxx>,=3D20
Mark.Randol@xxxxxxxxxx, si-list <si-list@xxxxxxxxxxxxx>
Subject: [SI-LIST] Re: Capacitors arrays. worth it or not?
Istvan,
=3D20
Yes, I ran the numbers:
=3D20
Electrical length of AVX 0508 LICC is =3D3D physical length * square =
root
=3D
of
Dielectric Constant.=3D20
The Dielectric Constant is somewhere above 10K. Let's use 10K.
=3D20
The wavelength is 4 time the quarter wavelength =3D3D 4 * the Electrical
length =3D3D 4 * 1.27 mm * square root of 10K.
=3D20
Frequency =3D3D C / wavelength =3D3D C / 4 * 1.27 mm * square root of =
10K =3D
=3D3D 590
MHz.=3D20
=3D20
But the resonance on the data sheet is 10 MHz.
=3D20
So I guess we are back to the lead inductance and the capacitance of the
MLCC causing the series resonance.
=3D20
And this lead inductance can be reduced with a reduction in the loop
area of the leads to the MLCC and by reducing the length of the leads. I
am guessing that is why the IDC and X2Y capacitors work. They reduce the
area of the loop of current feeding the capacitor. Is this correct?
=3D20
Best regards,
=3D20
John
=3D20
=3D20
=3D20
________________________________
From: Istvan.Novak@xxxxxxx [mailto:Istvan.Novak@xxxxxxx]=3D20
Sent: Wednesday, May 24, 2006 4:49 PM
To: Hill, John
Cc: steve weir; Larry Smith; Mark.Randol@xxxxxxxxxx; si-list
Subject: Re: [SI-LIST] Re: Capacitors arrays. worth it or not?
=3D20
John,
The series resonance frequency of the mounted capacitor does=3D20
not directly relate to the open-ended transmission line of=3D20
the capacitor body. The vertical transmission line that=3D20
Larry referred to has high losses, partly because of the metal=3D20
and dielectric losses, but also due to the electrical loading
of the plates. You can get this kind of model described in:
"Slow Wave Causal Model for Multi Layer Ceramic Capacitors"
on http://home.att.net/~istvan.novak/papers.html
Regards,
Istvan
Hill, John wrote:
Steve,
=3D20
I am not so sure of this. In the MLCC there is a transmission line with
an end that is open. It is the open 1/4 wavelength transmission line
that provides the low impedance on the other side of the part.
Specifically, a 1/4 wavelength away from the open is a short.=3D3D20
=3D20
In the IDC part the end is shorted, not open. There is a difference and
I am uncertain how to predict the resonance. That is why Larry's
viewpoint is important. It provided a better understand of the fields in
the parts and why the resonance occurs in the first place. I would like
to understand the IDC parts as well as we now understand the MLCC parts.
=3D20
Can anyone explain to me the physics behind the IDC resonance as
compared to the MLCC resonance?=3D3D20
=3D20
I would also like to know the Dielectric constant of the MLCC ceramic to
run the numbers and confirm the electrical length of the MLCC part. It
would be interesting to confirm the measured series resonance is truly
predicted by the 1/4 wavelength of the MLCC parts.
=3D20
John
=3D20
-----Original Message-----
From: steve weir [mailto:weirsi@xxxxxxxxxx]=3D3D20
Sent: Wednesday, May 24, 2006 4:12 PM
To: Hill, John; Larry Smith; Mark.Randol@xxxxxxxxxx; si-list
Subject: RE: [SI-LIST] Re: Capacitors arrays. worth it or not?
=3D20
John, the physics is the same for an IDC. The only difference is=3D3D20
that you multiple coupled lines in each part of Larry's model. =3D
Until=3D3D20
you get to really high frequency, you can simply replace those =
with=3D3D20
smaller equivalent inductance of Ls - Lm.
=3D20
Regards,
=3D20
=3D20
Steve.
At 10:59 AM 5/24/2006, Hill, John wrote:
=3D20
Larry,
=3D20
Your analysis of a capacitor as a transmission line is very
insightful.
It explains the physics behind why a MLCC has a series
resonance. I
=3D20
then
=3D20
tried to apply the same technique to an IDC capacitor with both
terminals of the capacitor on both sides of the part.
=3D20
I was not able to determine where the first resonance would be.
How
would you apply this technique to an IDC capacitor? And for that
matter
does anyone know where the first resonance would be for an IDC
capacitor?
=3D20
Best regards,
=3D20
John
=3D20
-----Original Message-----
From: Larry Smith [mailto:LSMITH@xxxxxxxxxx]
Sent: Tuesday, May 23, 2006 12:47 PM
To: weirsi@xxxxxxxxxx; Hill, John; Mark.Randol@xxxxxxxxxx;
si-list
Subject: RE: [SI-LIST] Re: Capacitors arrays. worth it or not?
=3D20
Steve, John - here is another interesting way to look at it.
When a
ceramic capacitor is mounted such that the capacitor plates are
=3D20
parallel
=3D20
to the PCB plates, the capacitor forms a vertical transmission
line
=3D20
with
=3D20
inductance per unit length and capacitance per unit length. The
far
=3D20
end
=3D20
of the transmission line is open circuit (air) and the near end
is
nearly shorted (PCB power planes present a very low impedance to
the
mounted capacitor). This makes a quarter wavelength resonator
similar
to a 50 Ohm transmission line that is open on one end. At the
quarter
wavelength frequency, the open circuit at the far end becomes a
low
impedance node at the near end. This is the series resonant
frequency
of the capacitor. The peaks and dips that you might see beyond
the
series resonance of the capacitor are associated with the half,
3/4,
full, 1 1/4, etc, wavelengths of the capacitor transmission
line.
=3D20
To see this effect, you must mount the capacitor on vias and
pads that
have less inductance than the capacitor itself otherwise the
resonance
is completely dominated by the mounting inductance. Tall
capacitors
with very low ESR show this effect the best. I was evaluating a
bunch
of capacitors one time and the 33nF NPO 2220 size capacitor
strongly
exhibited these properties. It is very tall and has low ESR
because of
the many, many plates. I had it mounted on a fixture estimated
at 83pH
but the inductance associated with the capacitor itself was
about 1 nH.
There were perhaps a half a dozen dips and peaks beyond series
=3D20
resonance
=3D20
associated with the transmission line properties of the
capacitor.
=3D20
David Hockanson and I did a couple of papers on this at 2002 and
2003
ECTC conference and another one at 2005 Design Con. You can
actually
use the transmission line properties of a capacitor to develop a
ladder
SPICE model and extract the element values. The model
accurately
predicts the reduction of inductance and the increase in ESR of
a
capacitor mounted on low inductance pads. This is important to
=3D20
simulate
=3D20
the parallel resonance that may occur between two capacitors or
between
a capacitor and power planes. Ceramic capacitors have a lot
more ESR
and less ESL than might be expected from a simple RLC model
beyond
series resonance.
=3D20
Mounting capacitors with the plates perpendicular to the PCB
planes
(rather than parallel) eliminates or at least greatly changes
this
mechanism. As Istvan mentioned, the resonances are very much
reduced.
I believe that there is still an increase in ESR and a reduction
of ESL
beyond series resonance as the current does not want to get very
far
away from the PCB power planes (big inductive loop). Once
again, you
would have to mount the capacitors on very low inductance mounts
in
order to see this.
=3D20
Regards,
Larry Smith
Altera Corporation
=3D20
=3D20
-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
=3D20
[mailto:si-list-bounce@xxxxxxxxxxxxx]
=3D20
On Behalf Of steve weir
Sent: Monday, May 22, 2006 11:27 PM
To: Hill, John; Mark.Randol@xxxxxxxxxx; si-list
Subject: [SI-LIST] Re: Capacitors arrays. worth it or not?
=3D20
John, you've got it. The vertical orientation makes for N very
small
cavities all acting in parallell. Hence, the secondary
resonance
occurs at a much higher frequency.
=3D20
Regards,
=3D20
=3D20
Steve.
At 01:50 PM 5/22/2006, Hill, John wrote:
=3D20
Steve,
=3D20
I'm sorry to be a little thick on this issue, but I may
be getting
=3D20
the
=3D20
two orientations confused. If I understand you
correctly, the
=3D20
following
=3D20
is true:
=3D20
It is Edie currents that keep the current concentrated
in the lower
plates of a capacitor when the capacitor is mounted
horizontally,
=3D20
which
=3D20
we are defining as having the plates parallel to the
board. This
=3D20
creates
=3D20
a resonate cavity under the part.
=3D20
When the capacitor is mounted with the plates
perpendicular to the
=3D20
board
=3D20
the current flows through all the plates.
=3D20
Is this correct?
=3D20
John
=3D20
=3D20
=3D20
=3D20
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-----Original Message-----
=3D20
From: steve weir [mailto:weirsi@xxxxxxxxxx]
Sent: Monday, May 22, 2006 2:41 PM
To: Hill, John; Mark.Randol@xxxxxxxxxx; si-list
Subject: Re: [SI-LIST] Re: Capacitors arrays. worth it
or not?
=3D20
John, when the plates of a cap are parallel to the
planes, eddy
currents block field penetration to the upper plates
through the
cavity. The field still goes around the terminal
metalization. This
makes a resonant cavity.
=3D20
Steve.
At 10:50 AM 5/22/2006, Hill, John wrote:
=3D20
Mark,=3D3D3D20
=3D20
We have uploaded an application note from
American Technical
=3D20
Ceramics
=3D20
concerning placing capacitors vertical and
horizontal. The URL is:
=3D20
=3D09
http://si-list.org/files/tech_files/ATC%20select_cap_wireless.pdf
=3D20
I have also sent an e-mail to the application
engineer about the
=3D20
issue
=3D20
of eddy currents limiting the field. The data in
the application
=3D20
note
=3D20
does not look like it supports the idea and I do
not understand the
physics.=3D3D3D20
=3D20
John
=3D20
=3D20
=3D3D3D20
=3D20
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-----Original Message-----
=3D20
From: si-list-bounce@xxxxxxxxxxxxx
=3D20
[mailto:si-list-bounce@xxxxxxxxxxxxx]
=3D20
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?
=3D20
=3D20
-----Original Message-----
From:
si-list-bounce@xxxxxxxxxxxxx=3D3D3D3D20
[mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Jerry
=3D20
Martinson
=3D20
=3D3D3D3D20
I've always wondered how discrete cap
performance is
=3D20
affected=3D3D3D3D20
=3D20
if the caps plates are parallel with the
underlying plane
=3D20
or=3D3D3D3D20
=3D20
if they are perpendicular. I'd think
that having them
=3D20
rolled=3D3D3D3D20
=3D20
90 degrees
(perpendicular) might make them perform
better in some=3D3D3D3D20
regions. I wonder how this would extend
to arrays and=3D3D3D3D20
whether arrays are configured rolled or
not. Does anyone=3D3D3D3D20
know? =3D3D3D3D20
=3D20
American Technical Ceramics (ATC) used to
recommend 'vertical'
=3D20
placement
=3D20
of their porcelain caps for just this reason.
I've seen it make
=3D20
several
=3D20
100MHz's of difference in the measured resonance
frequency. That
=3D20
was
=3D20
on
=3D20
a relatively thick 2 layer PCB, so on a board
with a thinner
=3D20
component
=3D20
to ground layer spacing this could be more
significant <guess>. I
didn't find it on their web site, but here is
their link.
=3D20
http://www.atceramics.com/
=3D20
Now how much of this was due to plate coupling
to the substrate, or
reduced effective capacitance and inductance
because of current
=3D20
crowding
=3D20
towards the new 'bottom' of all the plates,
beats me. It seems to
=3D20
me
=3D20
in
=3D20
the horizontal orientation, the upper plates
would have slightly
=3D20
more
=3D20
inductance due to the greater loop area. Which
effect dominates,
capacitance or inductance? =3D3D3D3D20
=3D20
The problem at the time was fixed, so we didn't
investigate
=3D20
further.
=3D20
--
Mark Randol, RF Evaluation & Application
Engineer
Not speaking for my company, etc
=3D09
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- Follow-Ups:
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- From: Istvan Novak - Board Design Technology
Other related posts:
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- » [SI-LIST] Re: Low-Q Controlled-ESR Bypass Capacitors
- [SI-LIST] Re: Low-Q Controlled-ESR Bypass Capacitors
- From: Istvan Novak - Board Design Technology