[SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator
- From: Michael Khusid <mkhusid@xxxxxxxxxx>
- To: 'Vishram Pandit ' <vishrampandit@xxxxxxxxxxx>
- Date: Tue, 12 Aug 2003 23:34:03 -0400
Vishram,
>I have seen some comments on the SI list that the capacitors are
>ineffective
>say above 500MHz. Is this really true??
It all depends on the type of capacitors (ESL, in particular) and on the way
they are connected to the planes. I've done some virtual experiments with
SIwave and was able to observe the effects of caps on impedance above
500MHz.
Mike Khusid
Application Engineer
Ansoft Corporation
www.ansoft.com
-----Original Message-----
From: Vishram Pandit
To: si-list@xxxxxxxxxxxxx
Sent: 8/12/03 11:26 PM
Subject: [SI-LIST] Re: UltraCAD ESR and Bypass Capacitor Caculator
The example I was referring to had a ground plane. However, with
simulations
and with experiments, we determined that the capacitors directly under
(bottom side of the board) the balls of the BGA performed better than on
the
top side. If we put the capacitors on the top side instead of at the
bottom,
EMI was worse at high frequencies (600 MHz- 800MHz). The harmonics of
the
BGAinternal frequencies were stronger. This was observed on multiple
designs
with the same BGA.
I have seen some comments on the SI list that the capacitors are
ineffective
say above 500MHz. Is this really true?? I have seen improvement in EMI
at
600MHz-800MHz if I tune the
* value of the capacitors
* ESR / ESL of the capacitors
* location of the capacitors
Any comments/advice will be appreciated.
Thanks,
Vishram
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