FreeLists / si-list / [SI-LIST] Re: Importance of Package Height

["Abe Riazi" <ARIAZI@xxxxxxxxxxx>]

Istvan Novak Wrote:
>
> As it was stated above, the lowest parallel modal resonance from a pair of
> FR4 10x5" planes is around 288MHz.  If the planes are ideal: perfectly
> rectangular, no cutouts, plane separation does not change with location,
and
> the dielectric material is homogenious, this parallel modal resonance
> frequency can be readily calculated as fres=1/(2*tpd), where tpd is the
> propagation delay along the longer side of the rectangular.  So as long as
> these idealization assumptions are valid, calculating the modal resonance
> frequencies is easy.

Dear Istvan:

Thank you for excellent comments.

In a paper by T. H. Hubing et al., (reference 1) on Page 158, equation 7 is:

fp = fs * sqrt(1 + n * C1/Cb )

Where fp and fs are parallel and series resonant frequencies respectively;
Cb  represents capacitance between power and ground planes,
and n is the number of decoupling caps having capacitance C1.

It is interesting to examine under what conditions above fp formula
simplifies
to your expression for parallel modal resonance fres=1/(2*tpd). This seems
to require setting n = 0 (causes fp = fs)  but leads to a mismatch factor of
1/pi;
assuming fp = fs = 1/[2 * pi * sqrt(L * C )] and tpd = sqrt(L * C).

Reference:

[1] T.H. Hubing, J.L. Drewniak, T.P. Van Doren and D.M. Hockanson,
 "Power Bus Decoupling on Multilayer Prined Circuit Boards", IEEE
Transactions on Electromagnetic Compatibility, Vol 37. No. 2,
 May 1995, PP. 155 - 166.

Best Regards,

Abe Riazi
ServerWorks






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