Hi all, this is a perfect application for the usage of a combination of 3D EM and RF circuit simulator. (just to make an example, CST Microwave studio and CSTDesign studio) Use the 3D simulator and perform a parametric analysis of your serpentine layout changing distance, lenght... and then use the parametric model in the circuit simulator to perfom time domain analysis. In this way it is easily possible to obtain both guideline s for your layout and/or accurate postlayout verification. Hope this helps Giancarlo ________________________________ Da: si-list-bounce@xxxxxxxxxxxxx per conto di wolfgang.maichen@xxxxxxxxxxxx Inviato: gio 23/10/2008 21.59 A: wolfgang.maichen@xxxxxxxxxxxx Cc: otter30@xxxxxxxxxxxxx; SI-List; si-list-bounce@xxxxxxxxxxxxx Oggetto: [SI-LIST] Re: Serpentine patterns for length matching A short correction - of course it should be "parasitic CAPACITANCE of the bends", not "inductance"! Wolfgang wolfgang.maichen@xxxxxxxxxxxx Sent by: si-list-bounce@xxxxxxxxxxxxx 10/23/2008 12:56 PM To otter30@xxxxxxxxxxxxx cc SI-List <si-list@xxxxxxxxxxxxx>, si-list-bounce@xxxxxxxxxxxxx Subject [SI-LIST] Re: Serpentine patterns for length matching Jim, parasitic inductance of the bends is a secondary effect with typical trace dimensions (<20mil trace width). What is more of a concern is the tight spacing you mention, which will cause significant crosstalk. The main effect of that will be that your actual delay through the serpentine will be LESS than what you'd expect given the geometric line length, dielectric constant etc. A simple picture is to think of part of the signal taking a shortcut hopping straight from segment to segment instead of following the trace. A closer investigation shows that in addition this also causes distortion of the output waveform, which is another undesired effect. Secondary corrections are current crowding at the in side if the bend (again lowering the prop delay) etc., but first you want to get the basic layout right. To reduce the effect of the bends (which each adds a small amount of parasitic capacitance, and if there are many bends even small contributions can add up), simply use two 45 degree bends instead of a single 90 degree bend, that gives you most of the necessary correction without the need to do any simulation. The simplest way to correct your layout is to require a spacing of about 3x the line width for striplines, or 5 - 6x the line width for surface microstrips. This effecteively reduces crosstalk to well below 1%. If out of some reason you absolutely can't increase the line-to-line spacing, at least make each line segment shorter that about 1/6th of your signal rise time to minimize signal distortion. In this case you'll need to use a 2.5D or 3D field solver to figure out how much your delay is reduced and then correct for that by adding more trace length. (Alternatively, manufacture a small test board with a single serpentine line, measure its delay and thus determine the correction factor experimentally). Wolfgang otter30@xxxxxxxxxxxxx Sent by: si-list-bounce@xxxxxxxxxxxxx 10/23/2008 08:21 AM To SI-List <si-list@xxxxxxxxxxxxx> cc Subject [SI-LIST] Serpentine patterns for length matching Hello, Does anyone know of general guidelines for the serpentine patterns used to match net lengths? We have a board with lots of diff pairs, and our board designer made the serpentines very tight. The separation between the adjacent bends of a pair is the same as the spacing of the traces in the pairs themselves. This seems to imply imedance variations if the trace widths don't change in the bends. Any insights would be greatly appreciated, Jim ------------------------------------------------------------------ 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 technical documents are available at: http://www.si-list.net <http://www.si-list.net/> 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 technical documents are available at: http://www.si-list.net <http://www.si-list.net/> 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 technical documents are available at: http://www.si-list.net <http://www.si-list.net/> 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 technical documents are available at: http://www.si-list.net 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