[SI-LIST] Re: Decoupling capacitor range required - PI Analysis
- From: istvan Novak <Istvan.Novak@xxxxxxx>
- To: "Lakshmi Narayanan Sowrirajan, TLS-Chennai" <lakshminarayanans@xxxxxx>
- Date: Wed, 08 Apr 2009 09:45:51 -0400
Hi,
The actual power distribution system is a multi-stage network, each
having its own frequency band
of operation where you need to care the parameters. On PCBs, and for
high-power rails, it is not
uncommon to have a cutoff frequency as low as a MHz, above which the
impedance of the board has a
diminishing effect on the target's (silicon's) behavior. The higher
frequency bands have to be taken
care of by package and chip decoupling.
Above the cutoff frequency of each stage you may have other constraints
(like return-path requirements,
avoiding EMI radiation), but those usually do not require you to
maintain the low target impedance
that you have to in the active frequency band.
Best regards,
Istvan Novak
SUN Microsystems
Lakshmi Narayanan Sowrirajan, TLS-Chennai wrote:
> Hi,
>
>
>
> In many papers and books I am seeing that the impedance has
> to be maintained across the frequency of interest, which one I have to
> take as my interested one is it KNEE frequency or is there any other
> formula specifically for PI.
>
>
>
> In the
> "Power_Distribution_Networks_with_On-Chip_Decoupling_Capacitors" book
> chapter six, summary it is mentioned as follows
>
>
>
> "In order to ensure correct and reliable operation of an IC,
> the impedance of the power distribution system should be maintained
> below the target impedance in the frequency range from DC to the maximum
> operating frequency"
>
>
>
> With this is it enough to keep the impedance constant
> (maintained at the Z target) up to 600MHz for a core voltage which is
> supplying a core operating at 600MHz.
>
>
>
>
>
> In the book by Istvan Novak "Power Distribution Network Design
> Methodologies" chapter 7 FDTIM method section 7.4 explains the need for
> on chip decaps and other important elements of the PDS which supports
> the target impedance, but in the tabulation at page 124 uses only up to
> 10pF capacitor whose resonance Frequency is 50.4MHz, is it given in a
> way assuming that after this the impedance will be met with the help of
> the on chip package and Die capacitance.
>
>
>
> Please clarify this. Thanks all for helping me in this PI topic.
>
>
>
>
>
> Thanks & Regards
>
> Lakshminarayanan.S
>
> 9840250902
>
>
>
>
>
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