[SI-LIST] : Re: Charge moving from decoupling capacitors

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From: Barry Ma (barry_ma@altavista.com)
Date: Wed May 17 2000 - 09:15:58 PDT


Steve,

Thanks a lot for the very nice hierarchy description below.

If there's a 10 mil or less spacing between pwr and gnd planes, the plane cap is available. The plane cap and the decaps are complementary in whole frequency range. Plane cap takes care of high end, and decaps cover low portion. Then the location of decaps are not critical. And then decaps can be shared by other chips, according to the excellent research conducted by EMC lab at UMR.

Please allow me to modify a bit your description as follows.

The capacitance inside the device supports the chip first, but usually not enough.
Charge from the planes also supports the chip and replenishes the device capacitance,
Decaps replenish the plane on low frequency portion, while plane cap responds itself on HF end,
Bulk capacitors replenish decaps and plane cap,
The voltage regulator replenishes the bulk capacitors.

Please correct me. Thanks.

Regards,
Barry
bma@ANRITSU.com
-----------------
From: "sweir" <weirsp@atdial.net>, on 5/11/00 9:28 PM:
....

The capacitance inside the device supports the chip,
Charge from the planes replenishes the device capacitance,
HF capacitors on the board replenish the planes,
Bulk capacitors replenish the HF capacitors,
The voltage regulator replenishes the bulk capacitors.

....[edited by bm]

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