From: glen herrmannsfeldt on
Symon <symon_brewer(a)hotmail.com> wrote:
> On 2/6/2010 8:13 AM, rickman wrote:
>> To be honest, I don't know
>> why they would put caps inside the package

> The caps are on the package because the inductance of the connecting
> vias and package balls means that, no matter how good the bypassing is
> on the PCB, the die on the package will have bypassing problems with
> it's supply. This is why I believe the high Q bypassing from a power
> plane and a ground plane doesn't help, and the layers can be arranged
> differently to achieve better results by optimising other areas.

I think what he means is that the resonance will still be too
low even inside the package.

-- glen
From: Symon on
On 2/6/2010 7:04 PM, glen herrmannsfeldt wrote:
> Symon<symon_brewer(a)hotmail.com> wrote:
>> On 2/6/2010 8:13 AM, rickman wrote:
>>> To be honest, I don't know
>>> why they would put caps inside the package
>
>> The caps are on the package because the inductance of the connecting
>> vias and package balls means that, no matter how good the bypassing is
>> on the PCB, the die on the package will have bypassing problems with
>> it's supply. This is why I believe the high Q bypassing from a power
>> plane and a ground plane doesn't help, and the layers can be arranged
>> differently to achieve better results by optimising other areas.
>
> I think what he means is that the resonance will still be too
> low even inside the package.
>
> -- glen


What resonance?
From: Symon on
On 2/6/2010 5:38 PM, rickman wrote:
>
> I keep asking you if you have done any real analysis or measurements
> of what you are stating?
>

Well, this was the first time you asked IIRC, but thank you for doing
so. The answer is "For sure". I've used Hyperlynx and Spice on my
boards. I guess you have also, or else you would not be able to post
your opinions without worrying you might giving someone a bum steer.

> I am no guru,

Really?

>
> but I was *very* impressed by
> what Lee Ritchey said just because he has full support for just about
> everything he stated in his course (except maybe that the food was
> good at the Chinese restaurant).
>
> Rick

You seem to be _very_ impressed. Almost as impressed as Steve Wier.

http://www.freelists.org/post/si-list/Lee-Ritcheys-book,4




From: Symon on
On 2/6/2010 6:15 PM, rickman wrote:
>> will increase with frequency.
>
> My point is that this is all theory. Unless you take some
> measurements to verify what you are saying, you can't say it is an
> accurate description of a real board and chip. Also consider that one
> via is not a power supply. Vias are used in parallel giving an
> effectively low impedance.
>
> Rick

Rick,
Do you measure every resistor you put on a board. Ohm's law is a theory,
after all.
Syms xx

From: glen herrmannsfeldt on
Symon <symon_brewer(a)hotmail.com> wrote:

(snip on bypass capacitors)

> What resonance?

The limit to the useful frequency range of a capacitor is
when it reaches resonance with the series (lead, package, etc.)
inductance. Graph impedance vs. frequency, when the reactive
component crosses zero that it resonance.

-- glen