Jack, I noticed that you had chosen to replace the 45s with the arc and not the other way around (i.e. replace the arcs with 45s). The reason why I'm curious about this is because I don't know how the algorithm commonly known as the 'Trace Modeler' represents (breaks down) an arc. For that matter, even handling short 45 degree or short orthogonal sections accurately may be a user-control issue. I'm talking in general terms here, not XTK specific, but I think 45s should be handled more consistently than arcs. I saw somewhere that you had done a straightening out exercise, but I'm interested to see what replacing the arcs with 45s yields - unless you told us and I missed it. Regards, Tony -----Original Message----- From: Jack W.C. Lin [mailto:JackWCLin@xxxxxxxxxxxx] Sent: Tuesday, October 08, 2002 7:46 PM To: Robert Haller; ericg@xxxxxxxxxxx Cc: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Serpentine Traces Dear all: As you know that serpentine routing will take shorter time to propagate signal from source to load than a straight line. But I found an interesting result from my case. In my DDR design,said some certain group. DQ length is almost the same with DQS,DQ did a serious serpentine routing but DQS a little. In our common sense,the flight time between them will differ a little. But I found that they differ too much,around 1.4 ns. DQS leading DQ? An unbelevable result. I found that DQ take 45 degree bending for serpentine, and DQS take ARC serpentine. If I modified all serpentine of DQ as ARC serpentine with same length, the flight time difference with DQS reduce to around 0.8ns. It's improved but not good enough. (my case is DDR333,flight_max=0.45ns,SIM tool is XTK). Is there any one experienced the similiar case? Any suggestion is highly appreciated. PS: I had delete all net but leave this problem DQ and related DQS, no other extra coupling but themself due to serpentine routing. Jack Jack W.C. Lin CAD&EMC Team in aopen In. ------i(c)l?T(r)?----- ?HYoaI: "Robert Haller" <rhaller@xxxxxxxxxx> ?HYo$e?A: 2002/9/11 $W$E 02:19:22 |?YoaI: "ericg@xxxxxxxxxxx" <ericg@xxxxxxxxxxx> 1/2AEY>: "si-list@xxxxxxxxxxxxx" <si-list@xxxxxxxxxxxxx> YD|(r): [SI-LIST] Re: Serpentine Traces Eric , For the example given, 176 ps/in -> 170 ps/in the difference was between 5/50 and 5/20 (Line width, /Line Spacing). The delay variations were even more dramatic at tighter spacings. To answer Andy's question, I click Info in Allegro - which I believe measures the center of the line. Regards, Bob -- Robert J. Haller (rhaller@xxxxxxxxxx) Principal Consultant Signal Integrity Software Inc. 6 Clock Tower Place, Suite 250 Maynard, MA 01754 Phone: (978) 461-0449, ext 15 Eric Goodill wrote: > Bob, > > What is 'close' in your test board? > > -Eric > > Robert Haller wrote: > > >>Praveen, >> This is a good question and has been raised before on the SI-LIST. >>Serpentine etch is often done to match clock lines or source syncronous >>data lines. >> >>I did bench testing of serpentine lines, in conjuction with simulations. >>I ran SPICE simulations using field solved 2d models then measured >>varying serpentine configurations. I examined impedance and propagation >>delay variations as a function of varying spacing, and signal edge rate. >> >>When transmission lines are serpentined 'close' to themselves the >>propagation delay decreases (The lines got faster). For example if I >>compare a straight control line and a sepertined line of the same length >>on the same layer, with all the fixturing nulled the propagation delay >>went from 176ps/in (straight line) to 170 ps/inch (serpentined line). >>You can think of the signal taking a shortcut across the distributed >>self capacitance of the closely serpentined lines. >>You might think a propagation delay reduction is good, but I also found >>the variability of prop velocity increased. I believe the variability >>increased because the capacitive coupling varies based on geometry, >>while normally the dielectric constant variations are the only source of >>prop delay variability (for a specific rise time and frequency). The >>variability is a small effect but is important when doing source >>syncronous designs. >> >> >>Regards, >>Bob > > > > ------------------------------------------------------------------ > To unsubscribe from si-list: > si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field > > or to administer your membership from a web page, go to: > //www.freelists.org/webpage/si-list > > For help: > si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field > > List archives are viewable at: > //www.freelists.org/archives/si-list > or at our remote archives: > http://groups.yahoo.com/group?I?/si-list/messages > Old (prior to June 6, 2001) list archives are viewable at: > http://www.qsl.net/wb6tpu > > -- Robert J. Haller (rhaller@xxxxxxxxxx) Principal Consultant Signal Integrity Software Inc. 6 Clock Tower Place, Suite 250 Maynard, MA 01754 Phone: (978) 461-0449, ext 15 ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http:?I?//groups.yahoo.com/group?I?/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net?I?/wb6tpu -- Binary/unsupported file stripped by Ecartis -- -- Type: application/ms-tnef ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu ------------------------------------------------------------------ To unsubscribe from si-list: si-list-request@xxxxxxxxxxxxx with 'unsubscribe' in the Subject field or to administer your membership from a web page, go to: //www.freelists.org/webpage/si-list For help: si-list-request@xxxxxxxxxxxxx with 'help' in the Subject field List archives are viewable at: //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu