[SI-LIST] : Another plane bypass question...

About this list Date view Thread view Subject view Author view

From: Bryan Ackerly (bryan@martin.com.au)
Date: Thu Sep 28 2000 - 23:42:19 PDT


I have a question regarding plane bypassing.

We have a board measuring 277 x 160mm which is a 4 layer board. With a
near field probe I can quite easily pick up noise from its exit cables
which seems to be fairly prominent at around 150, 300 and 500MHz.

I have done a two port network analyser sweep of the power plane which
reveals peaks near the frequencies listed above (no surprise) The board
has ground copper fill top and bottom and I have measured the plane
capacitance of the raw board at about 5nF (planes are assumed to be
0.5mm apart) The board has a number of 100nF and 10nF capacitors spread
across the board and a couple of tantalums for bulk charge.

Interesting (?) thing is that if I sweep a raw board without any bypass
capacitors, the insertion loss plot looks almost idential above about
120MHz!

I can go to 0.1mm (4mil) plane spacing without impacting cost. Without
extra copper fills this should give about 16nF of plane capacitance. I
have done some basic simulation with "real" capacitors which reveals
problems with parallel resonance peaks. I can damp them by adding a
small resistance (approx 1 ohm) in series with each capacitor.

Can anyone give me some practical advice here, particularly in view of
adding series resistance to control parallel resonances caused by the
plane capacitance?

--
----------------------------------------------------------------------
This email and any files transmitted with it are confidential and
intended solely for the use of the individual or entity to whom they
are addressed. If you have received this email in error please notify
the system manager.
                           Bryan Ackerly VK3YNG
    /\\\/\\\/\\\    /   /  Electronics Design Engineer
   /  \\\ \\\ \\\  /   /   87 Peters Ave, Mulgrave
  /   /\\\/\\\/\\\/   /    PO Box 4112, Mulgrave, Vic, 3170, AUSTRALIA
 /   /  \\\ \\\ \\\  /     Ph: +61 3 95609999  Fax: +61 3 95609055
/   /    \\\/\\\ \\\/      mailto: bryan@martin.com.au
    Tele-IP Pty Ltd        http://www.tele-ip.com
----------------------------------------------------------------------

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. 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 - 14:29:37 PDT