RE: [SI-LIST] : parasitic value for via

About this list Date view Thread view Subject view Author view

From: Ozgur Misman ([email protected])
Date: Sat Sep 16 2000 - 16:10:30 PDT


Hello Pierre,
I enjoyed your visualization. However, I think the factor of 2 is coming from
the fact that the seperation between the plates in your description is not d2-d1
rather it is r2-r1. r2=d2/2 and r1=d1/2. If you redo the calculation using
r2-r1 as plane seperation rather then d2 -d1 you will have an extra factor of 2
in the nominator. Then you will see your calculation will be consistent with
Johnson's.

Best Regards,
Ozgur Misman
Sr. Engineer

Pierre-Luc Cantin <[email protected]> on 09/16/2000 03:23:08 PM

Please respond to Pierre-Luc Cantin <[email protected]>
                                                              
                                                              
                                                              
 To: "'[email protected]'"
          <[email protected]>,
          "'[email protected]'" <[email protected]>
                                                              
 cc:
                                                              
                                                              
                                                              
 Subject: RE: [SI-LIST] : parasitic value for via
                                                              

Hello Chunho Lee,

I made once the effort to demonstrate Johnson via capacitance my-myself,
here is my demonstration and conclusion

- picture the via being a cylinder diameter=D1
- picture a second cylinder wrapped around the first one D2>D1
     - this second one represents power/gnd planes
- both cylinders are iso-potential
- un-fold both cylinders and you end up with two parallel plates.
     - the separation between the plates is the via clearance
1270-711(D2)
     - the height of both cylinders is the board thickness (T)
     - the width of the cylinder is the via circumference times
pi=3.1416... (pi*D1).

Now let do the math using Johnson example as a reference:

- er=4.7
- T=63mil ---> 1600um
- D1=28mil ---> 711um
- D2=50mil ---> 1270um

....Cvia = 1.41*4.7*0.063*0.028/(0.050-0.028) = 0.53pF

Now using two parallel plates capacitance formula:

Cvia= er*eo*A/d = er*eo*T*D1*pi/(D2-D1), eo=8.85aF/um

= 8.85aF/um*4.7*1600um*711um*pi/(1270um-711um)
= 265795aF = 0.265pF

Now here is something curious, if we then multiply again by 2

Cvia = 0.531pF !!! bang on

Assuming my demonstration process is fine,
have they assumed the circumference is 2*pi*diameter?
----------------------------------------------------------------------------
--------------------------

Pierre-Luc Cantin
Sr. ASIC Designer /
SI Team Leader

[email protected]
www.Hyperchip.com

phone (514) 931-5335 x217
fax. (514) 931-9923

COME MEET US AT:

Terabit Networking, Munich, Sept 20-22, Hyperchip presentation
Networld+Interop, Atlanta, Sept 26-28, Booth 3457
OptiComm 2000, Dallas, Oct 24-25, Richard Norman, Panelist
NGN, Washington, Oct 30-Nov 5, Booth 1010
SUPERnet, Santa Clara, Jan 14-17, Richard Norman, Panelist

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of
[email protected]
Sent: Saturday, September 16, 2000 1:08 AM
To: [email protected]
Subject: [SI-LIST] : parasitic value for via

Hello everyone.

I am looking for parasitic value for via.
and Dr Johnson's derivation is ...

  C=[1.41*Er*T*D1]/[D2-D1]
 where D2= diameter of clearance hole in GND plane,
       D1= diameter of pad surrounding via,
       T = thickness of PCB,
       Er= permeability.

parasitic inductance of via :
  L= 5.08h[ln(4h/d)+1]
 where h= length of via,
       d= diameter of via.

Let me explain
How this equation is derived?

thanks.

**********************************************
 Chunho Lee,
 Senior Engineer,

 SAMSUNG ELECTRONICS CO.,
 E-CIM, Management Innovation Team,
 416, Maetan-3dong, Paldal-gu,
 Suwon city, Korea
 Tel : 82-31-200-3097
 email: [email protected]
**********************************************

**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected]. In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****



**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected]. In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Tue May 08 2001 - 14:29:30 PDT