RE: High speed capacitors

["Don Wright" <dwright@seistl.com>]

I guess there really is still a need for us analog guys after all!  The
parameter that effects this issue is inductance.  Certain capacitor
materials/structures are highly inductive at high frequencies or fast signal
transitions.  Under certain conditions your capacitor could actually look
like an inductor to your signal which is obviously the opposite of your
intent.
   There are several different ways that you see this specified.  Some
manufacturers simply state that their caps are low inductance.  An older
measurement is dissipation factor which is given as a percentage (lower the
better).
   Still another way of specifying it is ESR (equivalent series resistance)
which is usually applied to larger caps that are used as power filters in
switching power supplies.
   This is unfortunately another one of those "engineering decision" type
issues where you have to trade off cost against performance.  The better the
cap, the more you're going to pay for it.
   Best of luck.

The digital world and the analog world always meet at RF frequencies (high
clock speeds).

Don Wright

-----Original Message-----
From: Dennis Fahey [mailto:dennisf@cisco.com]
Sent: Tuesday, June 06, 2000 2:43 PM
To: 'Eric de Jong'; pci-sig@znyx.com
Subject: RE: High speed capacitors


I'd recommend Marty Graham/Howard Johnson's book - "High Speed Digital
Design" -Prentice Hall; ISBN: 0133957241
... it has good insight on decoupling and high speed issues in general. He
writes in a good accessable style. His courses are very good too.
dennisf


-----Original Message-----
From:	Eric de Jong [SMTP:info@simultime.nl]
Sent:	Tuesday, June 06, 2000 7:27 AM
To:	pci-sig@znyx.com
Subject:	High speed capacitors

>From the book PCI hardware & software:

"However, the PCI bus specification does state that twelve 0.01 uF high
speed capacitors must be evenly spaced between the 3.3 volt and ground
layers."

What does the spec. mean with "high speed" capacitors?
e.g. the philips databook has the folowing capacitor ranges:
Class 1 NPO , Class 2 X7R, Y5V, Z5U

types of dielectric EIA/IEC, CECC:
COG/NPO/CG,
X7R/ 2R1,
Y5V/2F4,
Z5U/2E6

Who can shine a bit of light on this matter?

Eric de Jong.