Another thing I first saw about 20 years ago was "substrate mixing". Multiple oscillators were designed using an old 7404 inverter package. Because the substrate had significant inductance to reference, the noise acted as a parametric modulator on all the reverse biased junctions of the other sections of the IC.
Brent DeWitt > -----Original Message----- > From: [email protected] > [mailto:[email protected]]On Behalf Of Pettit, Ghery > Sent: Tuesday, March 22, 2005 9:50 AM > To: John Woodgate > Cc: [email protected] > Subject: RE: Radiated Emission Testing > > > John, > > Emissions may be harmonically related to clocks, they may be > intermodulation products or they may be non-harmonically related > to any of the above. For example, ringing on an improperly > terminated transmission line will be related to the length of the > line and the propagation velocity of the line and may or may not > have anything to do with the fundamental frequency of the signal > sent down the line that starting the ringing in the first place > (other than the rate at which energy is pumped into the ringing > signal). I've seen this ringing problem crop up when a board was > relayed out from a hand layout (nice curved corners, etc.) to a > machine layout with no component changes (type, value, location). > No way to quickly predict the presence of the emission until it > showed up in the lab one day. Previously compliant 9 track tape > drive suddenly went out of compliance with a new "identical" > unit. Took some real digging to find the problem and we had an > interesting discussion with ! > the drive vendor. That was about 20 years ago, but it really > sticks in your mind. > > Ghery This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to [email protected] Instructions: http://listserv.ieee.org/listserv/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas [email protected] Mike Cantwell [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
