FreeLists / si-list / [SI-LIST] Why is capacitor with high ESR

[zhangkun 29902 <zhang_kun@xxxxxxxxxx>]

Dear ALL

I am incharge of power integrity(PI) and electromagnetic inference(EMI) in 
Huawei Tech. In printed circuit board(PCB), the power ground plane pair 
composes of one resonant cavity, which could be studied by means of 2-dimension 
tansmission line theory.

According to the transmission line theory, when the transmission line is 
matched, there is no resonance. At the edge of PCB, the EM energy is reflected 
because the transmission line is OPEN. Traditional decoupling capacitors are of 
low ESR, which could not damping the resonance. Therefore I need capacitor with 
high ESR, whose ESR should be matched with the transmission line. On the other 
hand, the ESL is critical at high frequency. The ESL should be as small as 
possible. The package of capacitor mainly determines ESL so that the package 
should be as small as possible, such as 0402 or 0603. The capacitance should be 
as large as possible so that some benifit could be gotten at lower freqeuncy 
domain.

In DesignCon 2005, Cadence and Huawei will present one paper on this topic. The 
measurement results showed that the power ground noise is reduced about 10db 
and the far field EMI is reduced about 5db at several hundred MHz, when the 
capacitor of high ESR is applied. The frequency domain is extended to 1GHz 
where all the power ground noise and far field EMI could be reduced.

Best Regards

Zhangkun
2004.12.3


------------------------------------------------------------------
To unsubscribe from si-list:
si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field

or to administer your membership from a web page, go to:
http://www.freelists.org/webpage/si-list

For help:
si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field

List FAQ wiki page is located at:
                http://si-list.org/wiki/wiki.pl?Si-List_FAQ

List technical documents are available at:
                http://www.si-list.org

List archives are viewable at:     
                http://www.freelists.org/archives/si-list
or at our remote archives:
                http://groups.yahoo.com/group/si-list/messages
Old (prior to June 6, 2001) list archives are viewable at:
                http://www.qsl.net/wb6tpu