FreeLists / si-list / [SI-LIST] Re: Is Impedance Enough for Describing the PDS?

["Vijay B" <vijayis@xxxxxxxx>]

Hello,
        
          I am a student at SUNY and I am studying power integrity on a
PCB/package. I am studying it by analyzing the structural resonances due to
standing waves formed between the power and ground planes on a 2 plane
board.Different modes being excited being the cause of the different
resonances.
 
          We feel that is possible to a reasonable extent to control the
position of  the first resonant frequency on a given board - without the use
of decoupling capacitors. Possible upto the multi-GHz range. We have a
preliminary design on a 2 plane board without any components on it,  and we
have verified our results with simulation tools and a network analyzer. 

           I am very interested to know what the standards in the industry
are. For any given processor - upto what frequency is the power distribution
system designed to be stable. (what percent of the processor speed).   
           
          We considered only TEM waves. I am curious to know if TE and TM
waves are also being considered or if/when their effects will start being
felt.. 

          Any comments would be greatly appreciated. 

thanks, 

regards, 

vijay


----- Original Message ----- 
From: steve weir 
Date: Fri, 09 Jul 2004 14:06:41 -0700 
To: Zhangkun ,Abhijit Mahajan , si-list@xxxxxxxxxxxxx 
Subject: [SI-LIST] Re: Is Impedance Enough for Describing the PDS? 

>Zhangkun, 
>
>As I stated, the mounted inductance of IDC's and X2Y's is less than 1/3 the

>mounted inductance of ordinary 0603's using optimized two via mounts. The 
>inductance of the IDC / X2Y capacitors by themselves is even less, but as 
>you note the attachment inductance interferes. The reason that IDCs do 
>very well is that it takes four times as many via holes as a regular 
>capacitor. Done correctly, there is an almost proportionate decrease in 
>the attachment inductance. So, an IDC can be viewed as four 0603s, in 
>parallel but with only one part to mount. 
>
>The physics of the X2Y are a bit different. In cooperation with X2Y, I 
>have developed optimized mounts for X2Ys that use six vias and get results 
>essentially identical to the IDC with optimal mounts. This has been 
>verified by both simulation and measured results. The IDC's require 33% 
>more vias, and a much higher component cost to do the same decoupling job 
>as X2Ys. 
>
>Using either X2Y or IDCs we can cut component count by 3:1 or 
>better. Using X2Ys we reduce the BOM cost as well. Both Teraspeed and I 
>offer services to optimize PDS design to suite needs whether it is density,

>cost or some combination. There are probably other consultants available 
>who do as well. 
>
>Regards, 
>
>
>Steve. 
>At 07:46 PM 7/9/2004 +0800, Zhangkun wrote: 
>>Dear steve 
>>
>>IDC's, very expensive 
>>X2Ys, more than cheapy 0603 MLCCs but a lot less than IDCs 
>>NEC Proadlizer ( consult NEC on price ) 
>>
>>How about the value of the inductance of these kind of capacitors? When 
>>the cap is soldered on the PCB, there is leading inductance of about 1nH. 
>>This could not be eliminated by better caps. When the PCB is dency, the 
>>decoupling caps have to be put on the bottom. The leading inductance is 
>>larger. When the trace is used for PDS, the decoupling caps have to be put

>>near the IC. How many caps is enough? 
>>
>>What is the paper title which you mentioned, the Chris Cheng's? 
>>
>>Best Regards 
>>
>>Zhangkun 
>>2004.7.9 
>>
>>----- Original Message ----- 
>>From: "steve weir" 
>>To: "Abhijit Mahajan" ; 
>>Sent: Friday, July 09, 2004 4:40 PM 
>>Subject: [SI-LIST] Re: Is Impedance Enough for Describing the PDS? 
>>
>>
>>>Abhijit, yes localization is an approach that can be very helpful in 
>>>reducing or completely eliminating cavity resonance issues. For a long 
>>>time we have been able to get away with letting planes perform dual 
>>>duty: wide low impedance lumped conductors for power, and the return side

>>>of signal transmission lines. But we are long past the point where signal

>>>spectra is way beyond board lambda / 4. for common plane size / Er 
>>>combinations. Continued dual-use under these circumstances is an 
>>>invitation to EMC nightmares, and greatly complicates PDS 
>>realization. But 
>>>it does keep consultants like me busy. Sigrity, and Ansoft sell tools to 
>>>try and manage these problems. T he tools are very nice, but I think the 
>>>tools address the wrong problem. 
>>>
>>>If we "simply" eliminate the cavities ( OK shrink them so that they are 
>>not 
>>>problematic ), as you suggest then I think we are on the right 
>>>track. There is documentation out that clearly shows the economic 
>>benefits 
>>>of islanding power. In one recent paper, the author demonstrated that a 
>>>board with islanded power and 20mil power / ground separation performed 
>>>almost identically EMC-wise to the same size assembly using 2mil BC. The 
>>>tool and material vendors probably don't like hearing this. 
>>>
>>>Islanding power presents challenges with stack-up planning and 
>>routing. We 
>>>still have to: 
>>>
>>>1) Create a local low imped ance on the island, and 
>>>2) Get the DC current to the island 
>>>
>>>I see the tool opportunities in supporting these efforts, as the physics 
>>>and economics will really demand it. On the low-impedance island 
>>technique 
>>>end, I am a big fan of low inductance capacitors and optimized attachment

>>>techniques. The really low inductance capacitors that can be fitted to a 
>>>PWB today are: 
>>>
>>>IDC's, very expensive 
>>>X2Ys, more than cheapy 0603 MLCCs but a lot less than IDCs 
>>>NEC Proadlizer ( consult NEC on price ) 
>>>
>>>If done correctly, islanding can save a bundle, and goes directly to 
>>one of 
>>>Chris Cheng's pet mantra's that B/C is a solution looking for a 
>>>problem. We can avoid such problems and there fore the cost of B/C. 
>>>
>>>Steve. 
>>>At 01:06 PM 7/9/2004 +0530, Abhijit Mahajan wrote: 
>>>>Steve/Others. 
>>>>
>>>>Would it be better then to reduce the area of power planes as much as 
>>>>possible(by 
>>>>localizing the power planes to only cover the pins that need it) and
pack
>>>>the decoupling there? 
>>>>islands of same voltage can be then connected with wide traces to the 
>>>>nearest bulk cap 
>>>>And finally brought together at the regulator. 
>>>>
>>>>This can be vaguely be described as a "star topology" for power 
>>>>distribution. 
>>>>
>>>>Does anyone think there is any value in this appproach? Has it been 
>>>>discussed before? 
>>>>
>>>>
>>>>##I am assuming all signal routing is over a common ground plane. 
>>>>
>>>>
>>>>Thanks! 
>>>>
>>>>Abhijit. 
>>>>
>>>>
>>>>-----Original Message----- 
>>>>From: si-list-bounce@xxxxxxxxxxxxx 
>>[mailto:si-list-bounce@xxxxxxxxxxxxx] On 
>>>>Behalf Of steve weir 
>>>>Sent: Friday, July 09, 2004 6:04 AM 
>>>>To: zhang_kun@xxxxxxxxxx; si-list@xxxxxxxxxxxxx 
>>>>Subject: [SI-LIST] Re: Is Impedance Enough for Describing the PDS? 
>>>>
>>>>
>>>>Zhangkun, the problem is that the PDS overlaps both signal integrity and

>>>>EMC compliance. If the system rules are done right, then the PDS 
>>>>d ecoupling problem will eventually reduce to an impedance profile. But 
>>>>that profile is both spatial and frequency dependent. If I shove all the

>>>>decoupling capacitors into one corner of the board I get a very
different
>>>>result than if I distribute them. 
>>>>
>>>>Steve. 
>>>>At 08:04 AM 7/9/2004 +0800, zhangkun 29902 wrote: 
>>>>>Dear all 
>>>>>
>>>>>When talking about power delivery system with other engineer, there are

>>>>>a 
>>>>>lot of element to describe the PDS, such as energy storage, decoupling,

>>>>>bypassing, and so on. I think all these parameter could be described by

>>>>>one element, impedance of PDS. 
>>>>>
>>>>>Is my point right? Is impedanc e enough for describing the PDS? 
>>>>>
>>>>>Best Regards 
>>>>>
>>>>>Zhangkun 
>>>>>2004.7.9 
>>>>>
>>>>>------------------------------------------------------------------ 
>>>>>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 
>>>>>
>>>>
>>>>
>>>>------------------------------------------------------------------ 
>>>>To unsubscribe from si-list: 
>>>>si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field 
>>>>
>>>>or to administer your membership from a web p age, 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 
>>>>
>>>
>>>
>>>------ ------------------------------------------------------------ 
>>>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 
&g t; >>Old (prior to June 6, 2001) list archives are viewable at: 
>>>http://www.qsl.net/wb6tpu 
>>>
>>>
>
>
>------------------------------------------------------------------ 
>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 
>
>

-- 

___________________________________________________________
Sign-up for Ads Free at Mail.com
http://www.mail.com/?sr=signup[1] 

--- Links ---
   1 
http://mail01.mail.com/scripts/payment/adtracking.cgi?bannercode=adsfreejump01
------------------------------------------------------------------
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