So, you would predict that:=20 If I ran a trace on a 12" board and performed VNA on that trace, I should expect to see a "resonance" at 250MHz. If I took that same trace and ran it on a 24" board, I would see a resonance at 125MHz, and so on. (note that this time I have F indirectly propotional with board size - an oversight in my last posting). If this is the prediction, I am respectfully skeptical. And by the way, I didn't mean to imply that my experience in any other field besides power delivery was UN-limited! That's only true for the field of inducing errors in measurements and simulations. Jeff Loyer -----Original Message----- From: steve weir [mailto:weirsp@xxxxxxxxxx]=20 Sent: Wednesday, May 05, 2004 12:45 PM To: Loyer, Jeff Cc: si-list@xxxxxxxxxxxxx Subject: RE: [SI-LIST] Re: Is a copper plane not tied to any net a reference plane? Jeff, no, and I don't know where you get that idea. Lambda will be at=20 about 1/500MHz, lambda/2 at 250MHz, and lambda/4 at about 125MHz. A Tr of=20 2ns has a knee at about 250MHz, which coincides with lambda/2. Regards, Steve. At 12:39 PM 5/5/2004 -0700, Loyer, Jeff wrote: >If I understand you correctly, you predict that if I ran a trace on a >12" board and performed VNA on that trace, I should expect to see a >"resonance" at 100MHz. If I took that same trace and ran it on a 24" >board, I would see a resonance at 200MHz, and so on. > >If this is the prediction, I am respectfully skeptical. > >If this isn't the prediction, could you articulate how the phenomenon >would be reproduced, and how it would manifest itself? > >Perhaps you're talking about power distribution (where my experience is >admittedly limited)? In that case, could you answer the same questions? > >Thanks, >Jeff Loyer > >-----Original Message----- >From: steve weir [mailto:weirsp@xxxxxxxxxx] >Sent: Wednesday, May 05, 2004 11:09 AM >To: Loyer, Jeff >Cc: si-list@xxxxxxxxxxxxx >Subject: RE: [SI-LIST] Re: Is a copper plane not tied to any net a >reference plane? > >Jeff, sure it is just the propagation velocity of the wavefront. A 12" > >board at Er of 4 is 2nS 1 way delay. The round trip directly aligns on >a >2nS Tr/Tf. > >Regards, > > >Steve. >At 07:25 AM 5/5/2004 -0700, Loyer, Jeff wrote: > >Steve, > >Could you clarify what you meant about "the half-wave resonance of a >12" > >board"? Do you mean to say that you think a 12" board (I assume you're > >talking about a height or width dimension) will be susceptible to > >resonances at ~100MHz? If so, I'd like to understand that better. > > > > > >Jeff Loyer > > > > > >-----Original Message----- > >From: si-list-bounce@xxxxxxxxxxxxx >[mailto:si-list-bounce@xxxxxxxxxxxxx] > >On Behalf Of steve weir > >Sent: Tuesday, May 04, 2004 3:59 PM > >To: ericsilist@xxxxxxxxx; si-list@xxxxxxxxxxxxx > >Subject: [SI-LIST] Re: Is a copper plane not tied to any net a >reference > >plane? > > > >Eric, I believe Dr. Green provided a nice explanation for what happens > >to > >the current in your trace. However, that is hardly the end of the > >story. When you reference a signal, intentionally, or unintentionally > >against anything other than ground, you would be wise to consider what > >happens to that other reference. For your example case, it is pretty > >close > >to the half-wave resonance of a 12" board, resulting in efficient > >broadcasts to Zontar and other points East. Resonant cavities excited > >with > >substantial energy are generally not a good thing. > > > >Steve. > >At 02:16 PM 5/4/2004 -0700, eric steimle wrote: > > >I'm trying to settle an argument without saying which > > >side I'm on, and I was hoping someone could give a > > >quick and easy example to prove this. > > > > > >You have a four layer board that looked like this > > > > > >SIG1 > > >GND > > >VCC > > >SIG2 > > > > > >And the maximum rise time on the board was about 2ns > > >(say a 100MHz clock), then if I ran a trace from one > > >IC to another on SIG1 the return current would flow > > >along the GND plane (assuming no splits in the plane > > >etc.) > > > > > >What if I covered SIG1 with a plane of copper say > > >hovering 5 mil above SIG1, and then made the distance > > >between SIG1 and GND 100mil so.. > > > > > >Plane sheet of Copper > > >5 mil of air > > >SIG1 > > >100 mil FR4 > > >GND > > >VCC > > >SIG2 > > > > > >Now that plane sheet is not GND and it has no > > >association to any net it is just a continuous sheet > > >of copper about the size of the board. One of us > > >argues that the return current will continue to flow > > >along the GND plane as it did before. The other > > >argues that the return current will instead flow > > >mostly along that sheet of copper unitl it jumps back > > >to the GND plane as it gets closer to the IC. Any > > >help in this would be much appreciated. > > > > > >Thanks > > > > > > > > > > > > > > > > > >__________________________________ > > >Do you Yahoo!? > > >Win a $20,000 Career Makeover at Yahoo! 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