A neat trick I've used to measure the propagation delay. Instead of trying to pick off the delay from a TDR (you always have some accuracy issues with picking the starting and ending points) is to build a test stub. | | | C ---------------------------------- C Look at S21 between the two connectors and the frequency distance between the minimums will be the 1/2 wavelength. It's an easy relative measurement to pick off the curve. Even without a VNA - a simple frequency sweep provides very accurate results. Ed -----Original Message----- From: Ken Willis [mailto:kwillis@xxxxxxxxxxx]=20 Sent: Thursday, March 06, 2003 8:50 AM To: brian.butler@xxxxxxxxxxxxxxx; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Controlled Impedance Coupon Design H Brian Besides impedance, another critical aspect is the prop delay characteristics per layer. This gets really important whey you are trying to control skew between clock and data lines to 10's of picoseconds. The impedance coupons could help a lot if, instead of all the test lines on a layer just being a standard 6" length, there was an additional line that was a different known length on each layer. For example if there were an additional test line 4 inches long, then the engineer could figure out with a TDR the prop delay/inch for the various layers, and could more accurately design the skew offsets into the layout. I think this will be more and more important as we go along to higher speeds. This idea has been proposed on the SI-list more than once. I'm sure people are doing this on their own today, as I have done in the past. Ken=3D20 -----Original Message----- From: Brian Butler [mailto:brian.butler@xxxxxxxxxxxxxxx]=3D20 Sent: Tuesday, March 04, 2003 11:28 AM To: si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Controlled Impedance Coupon Design To All: The IPC task group which is rewriting the IPC-2141 Controlled Impedance =3D Circuit Boards and High Speed Logic Design is looking into the need of rewriting =3D the Controlled Impedance Coupon Design Rules (Section 4.7 of current =3D document) and would welcome your input on the following issues concerning controlled impedance coupon design. Please feel free to comment on any or all of = =3D the below listed points. Potential Topics for Controlled Impedance Design Rules 1) Terminate or un-terminated traces? 2) Test points are plated thru holes? 3) Size of Drilled Hole? 4) Size of pad? 5) Single-ended pitch between signal and ground? 6) Differential pitch and pattern? 7) Differential pattern (no ground reference, one ground reference, =3D two ground references)? 8) Width of coupon? 9) Length of test trace? 10) Use of thieving? 11) Need for consistent orientation of probe pads to eliminate the = =3D need for test operators to rotate the probe (repetitive stress)? 12) Bends in trace or no allowed bends? 13) Minimum spacing from one test structure to the next? 14) Type of nomenclature and clearance specifications? 15) Tie all ground/power planes together on coupon? 16) Ideal location of coupon(s) on panel? 17) Square lands to identify grounds/power reference points? 18) Other issues? ------------------------------------------------------------------ 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: =3D20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=3D20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =3D20 ------------------------------------------------------------------ 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: =20 //www.freelists.org/archives/si-list or at our remote archives: http://groups.yahoo.com/group/si-list/messages=20 Old (prior to June 6, 2001) list archives are viewable at: http://www.qsl.net/wb6tpu =20 ------------------------------------------------------------------ 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