Amund, That is why I wrote that the leads should hug close to the microprocessor package. Sort of like a piggy back, that way the lead loop inductance is at the minimum, since I guess correctly that the Vcc and Gnd pins are miles apart. I suppose it is not a mass production model, so it is acceptable to 'piggy back' the 100 pF decoupling cap across the microprocessor. I am assuming that the existing 'bulky' capacitor will take care of the voltage stabilizing requirement. In fact, 100 pF may too large under some circumstances and you are left with the option of splicing the Vcc and ground tracks (assuming they are running in parallel) and insert in a pair of surface mounted inductor to act like a common mode filter. Like what I did in my thesis all those years ago.
I had a 20dB reduction in radiated emission in the 180MHz to 300+ MHz band, just by introducing a pair of inductors to isolate the battery from the rest of the test circuit. The details of the layout is published in Chapter 5, page 81-83. My apologies, the site is a bit erratic and on my last try (just a min ago) has been temporarily put out of action, probably due to heavy traffic. http://www.geocities.com/timfoo6143 :-) Tim Foo amund@westin-emission. no To: <emc-p...@majordomo.ieee.org>, <[mailto:f...@np.edu.sg]> Sent by: cc: (bcc: Wan Juang Foo/ece/staff/npnet) owner-emc-pstc@majordo Subject: SV: Decoupling - capacitor values mo.ieee.org 04/18/02 04:53 PM Please respond to amund Interesting articles on your web-site, Tim. >BTW, how about just using a 100 pF capacitor with the 'leads' hugging close >to the microprocessor package There's a "mile" from the Vcc pin to ground, that's another problem. No ground plane, only ground traces which is routed around on the PCB. This product is soon leaving this world (it's an old product), but we are trying to let it exits a few more months before a new version is released. New emission requirements (24dBuV/m @ 3m, freq.band 155MHz-165MHz) might let it die very soon .... <snip> ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Ron Pickard: emc-p...@hypercom.com Dave Heald: davehe...@attbi.com For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: http://ieeepstc.mindcruiser.com/ Click on "browse" and then "emc-pstc mailing list"
