Re: [SI-LIST] : Re: Diff probes for tdr.

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From: Mike Jenkins (jenkins@lsil.com)
Date: Fri Oct 20 2000 - 15:50:30 PDT


Ron,

Another issue in not connecting dif'l probe ground to DUT ground
is that the probe does not then correctly back-terminate the
common mode. If the load (i.e., DUT) is a balanced load, this
does not matter. But if it's not balanced, some common mode
will be reflected. The measurement theory assumes that such
reflections would be absorbed, but, without ground, they won't.

In most cases, this is probably a small difference, but I guess
I prefer theoretical correctness, other things being equal.

Regards,
Mike Jenkins
LSI Logic

Ron Miller wrote:
>
> brrn doing it for years.
>
> ron
>
> > -----Original Message-----
> > From: Bob Lewandowski
> > Sent: Friday, October 20, 2000 12:18 PM
> > To: Ron Miller
> > Cc: 'Bob Lewandowski'; Ken Taylor; si-list@silab.eng.sun.com
> > Subject: Re: [SI-LIST] : Re: Diff probes for tdr.
> >
> > I'd be real cautious about not tying down grounds and relying on the power
> > cord/chassis interconnects to eliminate common mode signals between the scope common
> > and the DUT power supply common. TDR/sampling heads are DC coupled, and can easily be
> > overwhelmed by even a low frequency signal that exceeds their common mode range, or
> > upsets the sampling head bias. The ground between differential signals is only
> > "virtual".
> >
> > ---Bob Lewandowski
> >
> > Ron Miller wrote:
> >
> > > Good comments Bob
> > >
> > > If you are measuring a differential line, though, you do not
> > > have to connect the ground. All you are really intrested in
> > > is the differential impedance. The impedance to ground is
> > > irrelevant, because you have a virtual ground half way between
> > > the two differential drive pins anyway.
> > >
> > > Ron Miller
> > >
> > > > -----Original Message-----
> > > > From: Bob Lewandowski
> > > > Sent: Thursday, October 19, 2000 7:04 PM
> > > > To: Ken Taylor
> > > > Cc: si-list@silab.eng.sun.com
> > > > Subject: Re: [SI-LIST] : Re: Diff probes for tdr.
> > > >
> > > > I concur with all the semi-rigid coax comments. Most all of the commercial
> > > > probes I've seen generate large launch discontinuities (~20%), with the
> > > > exception of Picoprobe, and Cascade Microtech (both $$$ !).
> > > >
> > > > I've used .047" diameter coax, either solid jacket or the tin dipped braid type
> > > > (very flexible). Tensolite/QMI sell .047 cable assemblies of the braid type
> > > > with male or female SMAs, that they call Semi-Flex. Just buy a 1 ft. cable and
> > > > chop it in half, match the lengths for differential. With the small coax you
> > > > can solder the jacket to a board ground next to a trace, and with a very short
> > > > center conductor, keep the launch reflection down to around 5%. Semi-rigid coax
> > > > typically can be obtained with tight tolerance on the Z0, so the cable becomes a
> > > > good reference impedance before the launch. Be cautious about minimizing the
> > > > length, as the small stuff is pretty lossy and degrades rise time.
> > > >
> > > > ---Bob Lewandowski
> > > > Vixel Corp.
> > > >
> > > > Ken Taylor wrote:
> > > >
> > > > > John Fisher's solution below is a very good one that I have used
> > > > > extensively. Although a little clumsy mechanically (you will want to use a
> > > > > probe positioner, hold the probe at about 45 degrees to get the tips and the
> > > > > ground to contact, keep the tips and ground path VERY short like 2 mm or so)
> > > > > they give great results. One more thing, however: If the probe impedance
> > > > > doesn't match your DUT impedance, you will get reflections etc. and you
> > > > > won't be able to see anything close in to the contact point. To solve that,
> > > > > match the impedances as closely as possible, keep the probe (semi rigid
> > > > > stuff) more than, say, 6" long, and then all the mismatch will be at the
> > > > > flexible cable/probe connection, and you can keep it out of the way of your
> > > > > measurements. These probes work well for 17 pS Tr.
> > > > > One last thing, these things were whipped up for customers by friendly Tek
> > > > > AEs, and weren't part numbered for sale. (How can you charge $5000 for these
> > > > > things? Can't, so they don't sell them!) The real Tek (and Agilent) probes
> > > > > looked nice, are definitely nicer mechanically, but can't hold a light to
> > > > > these "do it yourself" probes.
> > > > >
> > > > > Regards, Ken.
> > > > >
> > > > > Ken Taylor
> > > > > Polar Instruments, Portland, OR, USA.
> > > > > ken.taylor@polarinstruments.com
> > > > >
> > > > > John said
> > > > > <<We have built these using equal length sections of semi rigid coax with
> > > > > sma's at one end. The semi rigid copper outer shield is soldered together>
> > > > > approx. every 3 &quot;.&nbsp; Prepare the ends by careful cutting of the
> > > > > shield with an exacto knife,&nbsp; than solder the center conductors to
> > > > > the launch point vias or pads. Tektronix shipped some of&nbsp; these to
> > > > > us as accessories when we bought their IPA-510 a few years ago.&nbsp; I
> > > > > might be able to find a tek part number but someone like Micro-Coax could
> > > > > make some for you or find an off the shelf semi rigid assembly with sma's
> > > > > on both ends and then just cut it in half. Be carful not to bend it too
> > > > > much and kink it.&nbsp; These can also make nice 50 Ohm 10x passive
> > > > > probes with the addition of a series 450 resistor at the end.<br> >>
> > > > >
> > > > > ----- Original Message -----
> > > > > From: "si-list-digest" <owner-si-list@silab.eng.sun.com>
> > > > > To: <si-list-digest@silab.eng.sun.com>
> > > > > Sent: Thursday, October 19, 2000 5:00 PM
> > > > > Subject: si-list-digest V1 #286>
> > > > >
> > > > > >
> > > > > > si-list-digest Thursday, October 19 2000 Volume 01 : Number
> > > > > 286
> > > > > >
> > > > > >
> > > > > >
> > > > > > In this issue:
> > > > > >
> > > > > > 1.) [SI-LIST] : High Frequency Seminar
> > > > > > "chasgra" <chasgra@email.msn.com>
> > > > > >
> > > > > > 2.) [SI-LIST] : SI - Salary Survey
> > > > > > sainath nimmagadda <nescafe@dacafe.com>
> > > > > >
> > > > > > 3.) [SI-LIST] : Differential TDR probes
> > > > > > "zanella, fabrizio" <zanella_fabrizio@emc.com>
> > > > > >
> > > > > > 4.) Re: [SI-LIST] : Differential TDR probes
> > > > > > "Ritesh Kapahi" <rkapahi@idt.com>
> > > > > >
> > > > > > 5.) Re: [SI-LIST] : Differential TDR probes
> > > > > > Salvador_Aguinaga@3com.com
> > > > > >
> > > > > > 6.) RE: [SI-LIST] : Differential TDR probes
> > > > > > "Daniel, Erik S." <Daniel.Erik@mayo.edu>
> > > > > >
> > > > > > 7.) Re: [SI-LIST] : Differential TDR probes
> > > > > > John Fisher <jmfisher@cisco.com>
> > > > > >
> > > > > >
> > > > > > ----------------------------------------------------------------------
> > > > > >
> > > > > > Date: Wed, 18 Oct 2000 18:30:58 -0700
> > > > > > From: "chasgra" <chasgra@email.msn.com>
> > > > > > Subject: [SI-LIST] : High Frequency Seminar
> > > > > >
> > > > > > This is a multi-part message in MIME format.
> > > > > >
> > > > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0
> > > > > > Content-Type: text/plain;
> > > > > > charset="iso-8859-1"
> > > > > > Content-Transfer-Encoding: quoted-printable
> > > > > >
> > > > > > Rocky Mountain Chapter EMC Society presents:
> > > > > >
> > > > > > High Frequency Measurements and Noise in Electronic Circuits
> > > > > > - - one day demonstration based seminar.
> > > > > >
> > > > > > An informative and entertaining multimedia seminar for digital and =
> > > > > > analog designers as well as test engineering and EMC personnel.=20
> > > > > >
> > > > > > by Douglas C. Smith=20
> > > > > >
> > > > > > Author of High Frequency Measurements and Noise in Electronic Circuits=20
> > > > > >
> > > > > > An Unusual Seminar - Sign up here.
> > > > > >
> > > > > > This seminar is unique. Demonstrations on real circuits are used to =
> > > > > > illustrate most of the concepts being taught unlike most seminars which =
> > > > > > are taught through the use of vu-graphs as the main medium. About 70% of =
> > > > > > class time is spent in demonstrations. Complicated math is avoided. This =
> > > > > > format makes the seminar more interesting to the students and helps them =
> > > > > > to achieve a deeper understanding of the material covered. Many students =
> > > > > > have said that this was the best technical seminar they ever attended!=20
> > > > > >
> > > > > >
> > > > > >
> > > > > > When: Dec 1 2000
> > > > > >
> > > > > > If you are interested then goto our weblink: =
> > > > > > http://www.ewh.ieee.org/r5/denver/rockymountainemc
> > > > > >
> > > > > > Look for the Dec 1 meeting link and sign up!!
> > > > > >
> > > > > > Charles Grasso
> > > > > > Vice Chair RMCEMCS
> > > > > >
> > > > > >
> > > > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0>
> > > > > > Content-Type: text/html;
> > > > > > char> set="iso-8859-1"
> > > > > > Content-Transfer-Encoding: quoted-printable
> > > > > >
> > > > > > <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
> > > > > > <HTML><HEAD>
> > > > > > <META content=3D"text/html; charset=3Dwindows-1252" =
> > > > > > http-equiv=3DContent-Type>
> > > > > > <META content=3D"MSHTML 5.00.2919.6307" name=3DGENERATOR></HEAD>
> > > > > > <BODY bgColor=3D#ffffff>
> > > > > > <DIV><FONT size=3D2>
> > > > > > <P align=3Dcenter><A name=3DTitle><FONT size=3D6>Rocky Mountain Chapter =
> > > > > > EMC=20
> > > > > > Society</FONT></A><FONT size=3D6> presents:</FONT></P>
> > > > > > <P align=3Dcenter><FONT color=3D#0000ff face=3DArial size=3D6><B>High =
> > > > > > Frequency=20
> > > > > > Measurements and Noise</B></FONT> <FONT color=3D#0000ff face=3DArial =
> > > > > > size=3D6><B>in=20
> > > > > > Electronic Circuits<BR></B></FONT><FONT color=3D#0000ff face=3DArial =
> > > > > > size=3D5><B>- one=20
> > > > > > day demonstration based seminar.</B></FONT></P>
> > > > > > <P align=3Dcenter><FONT size=3D5><I>An informative and </I></FONT><FONT=20
> > > > > > color=3D#ff0000 size=3D5><B><I><U>entertaining</U></I></B></FONT><FONT =
> > > > > > size=3D5><I>=20
> > > > > > multimedia seminar for digital and analog designers as well as test =
> > > > > > engineering=20
> > > > > > and EMC personnel.</I></FONT> </P>
> > > > > > <P align=3Dcenter><FONT face=3DArial size=3D4><B>by </B></FONT><A=20>
> > > > > > href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/1dayemc.htm#Ab=
> > > > > > out The Instructor"><FONT=20
> > > > > > face=3DArial size=3D4><B>Douglas C. Smith</B></FONT></A> </P>
> > > > > > <P align=3Dcenter><FONT size=3D4>Author of <I>High Frequency =
> > > > > > Measurements and Noise=20
> > > > > > in Electronic Circuits</I></FONT> </P>
> > > > > > <P align=3Dcenter><A=20
> > > > > > href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc/seminarsignup.=
> > > > > > htm"><FONT=20
> > > > > > size=3D5><B><U>An Unusual Seminar - Sign up here.</U></B></FONT></A></P>
> > > > > > <P align=3Dleft>This seminar is unique. Demonstrations on real circuits =
> > > > > > are used=20
> > > > > > to illustrate most of the concepts being taught unlike most seminars =
> > > > > > which are=20
> > > > > > taught through the use of vu-graphs as the main medium. About 70% of =
> > > > > > class time=20
> > > > > > is spent in demonstrations. Complicated math is avoided. This format =
> > > > > > makes the=20
> > > > > > seminar more interesting to the students and helps them to achieve a =
> > > > > > deeper=20
> > > > > > understanding of the material covered. Many students have said that this =
> > > > > > was the=20
> > > > > > <I>best</I> technical seminar they ever attended! </P>
> > > > > > <P align=3Dleft>&nbsp;</P>
> > > > > > <P align=3Dleft>When: Dec 1 2000</P>
> > > > > > <P align=3Dleft>If you are interested then goto our weblink: <A=20
> > > > > > href=3D"http://www.ewh.ieee.org/r5/denver/rockymountainemc">http://www.ew=
> > > > > > h.ieee.org/r5/denver/rockymountainemc</A></P>
> > > > > > <P align=3Dleft>Look for the Dec 1 meeting link and sign up!!</P>
> > > > > > <P align=3Dleft>Charles Grasso<BR>Vice Chair=20
> > > > > > RMCEMCS</P></FONT></DIV></BODY></HTML>
> > > > > >
> > > > > > - ------=_NextPart_000_000C_01C03931.8EE7A3A0--
> > > > > >
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 11:44:46 -0800
> > > > > > From: sainath nimmagadda <nescafe@dacafe.com>
> > > > > > Subject: [SI-LIST] : SI - Salary Survey
> > > > > >
> > > > > > Hi SI folks:
> > > > > >
> > > > > > I understand that with growing complexity in multimedia technology, SI
> > > > > > positions are getting increasingly challenging (we see "PhD preferred">
> > > > > > in ads)and hopefull> y lucrative too. We often find salary surveys for
> > > > > > mainstream folks such as IT professionals. I am just curious if there is
> > > > > > some kind of salary survey for SI folks too. I am sure that helps us SI
> > > > > > folks have an idea where we stand in this dynamic market.
> > > > > >
> > > > > > Best,
> > > > > >
> > > > > > SN
> > > > > > _____________________________________________________________
> > > > > > Tired of limited space on Yahoo and Hotmail?
> > > > > > Free 100 Meg email account available at http://www.dacafe.com
> > > > > >
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 15:44:15 -0400
> > > > > > From: "zanella, fabrizio" <zanella_fabrizio@emc.com>
> > > > > > Subject: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > > We're having problems getting a good high frequency launch when probing pc
> > > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > > anyone
> > > > > > found good differential TDR probes which allow you to measure very closely
> > > > > > spaced points on pc boards or cables?
> > > > > >
> > > > > > Thanks and regards,
> > > > > > Fabrizio Zanella
> > > > > > Hardware Engineering
> > > > > > EMC Corporation
> > > > > > fzanella@emc.com
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to>
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUB> SCRIBE
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> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 14:12:22 -0700
> > > > > > From: "Ritesh Kapahi" <rkapahi@idt.com>
> > > > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > > Agilent has got some micro probe which is an accessory for their high
> > > > > > bandwidth scope 86100 and differential TDR module 54754A . It usually has
> > > > > a
> > > > > > long lead times (3-4 months)
> > > > > > Bye
> > > > > > Kaps
> > > > > >
> > > > > > - ----- Original Message -----
> > > > > > From: zanella, fabrizio <zanella_fabrizio@emc.com>
> > > > > > To: SI List (E-mail) <si-list@silab.eng.sun.com>
> > > > > > Sent: Thursday, October 19, 2000 12:44 PM
> > > > > > Subject: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > >
> > > > > > > We're having problems getting a good high frequency launch when probing
> > > > > pc
> > > > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > > > anyone
> > > > > > > found good differential TDR probes which allow you to measure very
> > > > > closely
> > > > > > > spaced points on pc boards or cables?
> > > > > > >
> > > > > > > Thanks and regards,
> > > > > > > Fabrizio Zanella
> > > > > > > Hardware Engineering
> > > > > > > EMC Corporation
> > > > > > > fzanella@emc.com
> > > > > > >
> > > > > > >
> > > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > > ****
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
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> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------>
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 16> :39:38 -0500
> > > > > > From: Salvador_Aguinaga@3com.com
> > > > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > > Kaps,
> > > > > >
> > > > > > Have you comfirmed that the TDR Module 54754A works with their new 86100A
> > > > > main
> > > > > > frame?
> > > > > > They (their sales guys) tell me that it will not be ready until Dec 00.
> > > > > >
> > > > > > Thanks,
> > > > > > - -- Sal
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > "Ritesh Kapahi" <rkapahi@idt.com> on 10/19/2000 04:12:22 PM
> > > > > >
> > > > > > Please respond to "Ritesh Kapahi" <rkapahi@idt.com>
> > > > > >
> > > > > > Sent by: "Ritesh Kapahi" <rkapahi@idt.com>
> > > > > >
> > > > > >
> > > > > > To: "zanella, fabrizio" <zanella_fabrizio@emc.com>, "SI List
> > > > > > cc: (Salvador Aguinaga/MW/US/3Com)
> > > > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > >
> > > > > >
> > > > > > Agilent has got some micro probe which is an accessory for their high
> > > > > > bandwidth scope 86100 and differential TDR module 54754A . It usually has
> > > > > a
> > > > > > long lead times (3-4 months)
> > > > > > Bye
> > > > > > Kaps
> > > > > >
> > > > > > - ----- Original Message -----
> > > > > > From: zanella, fabrizio <zanella_fabrizio@emc.com>
> > > > > > To: SI List (E-mail) <si-list@silab.eng.sun.com>
> > > > > > Sent: Thursday, October 19, 2000 12:44 PM
> > > > > > Subject: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > >
> > > > > > > We're having problems getting a good high frequency launch when probing
> > > > > pc
> > > > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > > > anyone
> > > > > > > found good differential TDR probes which allow you to measure very
> > > > > closely
> > > > > > > spaced points on pc boards or cables?
> > > > > > >
> > > > > > > Thanks and regards,
> > > > > > > Fabrizio Zanella
> > > > > > > Hardware Engineering
> > > > > > > EMC Corporation
> > > > > > > fzanella@emc.com
> > > > > > >
> > > > > > >
> > > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > > si-list archives are accessible at > http://www.qsl.net/wb6tpu
> > > > > > > ****
> > > > > > >
> > > > > > >
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 17:26:16 -0500
> > > > > > From: "Daniel, Erik S." <Daniel.Erik@mayo.edu>
> > > > > > Subject: RE: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > > Fabrizio-
> > > > > >
> > > > > > A couple things we have used with some success for diff TDR on PC boards
> > > > > and
> > > > > > chip packages:
> > > > > >
> > > > > > 1. GGB Picoprobe Model 10
> > > > > > - --------------------------
> > > > > > These are micro-coax probes with needle-like tips connected at the end.
> > > > > > They are pretty cheap, and there are a wide variety of options (different
> > > > > > needle tip lengths, widths, materials, ...). We have used two
> > > > > ground-signal
> > > > > > style probes soldered together to form a GSSG style differential probe.
> > > > > The
> > > > > > needles are flexible and can be bent to accommodate different board
> > > > > > geometries (although bending the needles too much definitely degrades the>
> > > > > > launch). There are some technical drawbacks to these, but they have come
> > > > > in
> > > > > > handy for troubleshooting.
> > > > > >
> > > > > > 2. GGB Picoprobe Model 40A Dual probes
> > > > > > - ---------------------------------------
> > > > > > These are very good microwave probes (with an advertised 40 GHz bandwidth)
> > > > > > that you can buy in GSSG or GSGSG styles in a variety of pitches. They
> > > > > are
> > > > > > fairly expensive, the lead times are long for custom orders, and I would
> > > > > not
> > > > > > recommend trying to bend these(!) to accommodate different geometries, but
> > > > > > they are electrically very good.
> > > > > >
> > > > > > There are a number of other similar microwave probes we have used in
> > > > > various
> > > > > > special cases, but I think I have used these two options the most.
> > > > > >
> > > > > > - Erik
> > > > > >
> > > > > > ==================================================================
> > > > > > Erik Daniel, Ph.D. Mayo Foundation
> > > > > > Voice: (507) 284-1634 Guggenheim 1011B
> > > > > > Fax: (507) 284-9171 200 First Street SW
> > > > > > E-mail: daniel.erik@mayo.edu Rochester, MN 55905
> > > > > > ==================================================================
> > > > > >
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: zanella, fabrizio [mailto:zanella_fabrizio@emc.com]
> > > > > > > Sent: Thursday, October 19, 2000 2:44 PM
> > > > > > > To: SI List (E-mail)
> > > > > > > Subject: [SI-LIST] : Differential TDR probes
> > > > > > >
> > > > > > >
> > > > > > > We're having problems getting a good high frequency launch
> > > > > > > when probing pc
> > > > > > > boards and cable differential pairs when taking TDR
> > > > > > > measurements.Has anyone
> > > > > > > found good differential TDR probes which allow you to measure
> > > > > > > very closely
> > > > > > > spaced points on pc boards or cables?
> > > > > > >
> > > > > > > Thanks and regards,
> > > > > > > Fabrizio Zanella
> > > > > > > Hardware Engineering
> > > > > > > EMC Corporation
> > > > > > > fzanella@emc.com
> > > > > > >
> > > > > > >
> > > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
> > > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > > ****
> > > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE>
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> > > > > > si-list archives are accessible at http://www.qsl.net/wb6tpu
> > > > > > ****
> > > > > >
> > > > > > ------------------------------
> > > > > >
> > > > > > Date: Thu, 19 Oct 2000 15:38:44 -0700
> > > > > > From: John Fisher <jmfisher@cisco.com>
> > > > > > Subject: Re: [SI-LIST] : Differential TDR probes
> > > > > >
> > > > > > <html>
> > > > > > <font size=3>Fabrizio,<br>
> > > > > > <br>
> > > > > > We have built these using equal length sections of semi rigid coax with
> > > > > > sma's at one end. The semi rigid copper outer shield is soldered together
> > > > > > approx. every 3 &quot;.&nbsp; Prepare the ends by careful cutting of the
> > > > > > shield with an exacto knife,&nbsp; than solder the center conductors to
> > > > > > the launch point vias or pads. Tektronix shipped some of&nbsp; these to
> > > > > > us as accessories when we bought their IPA-510 a few years ago.&nbsp; I
> > > > > > might be able to find a tek part number but someone like Micro-Coax could
> > > > > > make some for you or find an off the shelf semi rigid assembly with sma's
> > > > > > on both ends and then just cut it in half. Be carful not to bend it too
> > > > > > much and kink it.&nbsp; These can also make nice 50 Ohm 10x passive>
> > > > > > probes with the addition of a series 450 resistor at the end.<br>
> > > > >> > <br>
> > > > > > Regards<br>
> > > > > > <br>
> > > > > > John<br>
> > > > > > <br>
> > > > > > At 03:44 PM 10/19/00 -0400, you wrote:<br>
> > > > > > <blockquote type=cite cite>We're having problems getting a good high
> > > > > > frequency launch when probing pc<br>
> > > > > > boards and cable differential pairs when taking TDR measurements.Has
> > > > > > anyone<br>
> > > > > > found good differential TDR probes which allow you to measure very
> > > > > > closely<br>
> > > > > > spaced points on pc boards or cables?<br>
> > > > > > <br>
> > > > > > Thanks and regards,<br>
> > > > > > Fabrizio Zanella<br>
> > > > > > Hardware Engineering<br>
> > > > > > EMC Corporation<br>
> > > > > > fzanella@emc.com<br>
> > > > > > <br>
> > > > > > <br>
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to<br>
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put:
> > > > > > UNSUBSCRIBE<br>
> > > > > > si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.<br>
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> > > > > eudora="autourl">http://www.qsl.net/wb6tpu><br>
> > > > > > ****</font></blockquote><br>
> > > > > >
> > > > > <div>*********************************************************************</
> > > > > div>
> > > > > > <div>John M. Fisher -- Cisco Systems&nbsp; --
jmfisher@cisco.com</div>
> > > > > > <div>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; 170 W. Tasman Dr., Bldg G, San Jose
> > > > > > CA 95134-1706</div>
> > > > > >
> > > > > <div><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</x-tab>&nbsp;&n
> > > > > bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;
> > > > > > __&nbsp;&nbsp;&nbsp;
> > > > > >
> > > > > _&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nb
> > > > > sp;&nbsp;&nbsp;&nbsp;&nbsp;
> > > > > > _</div>
> > > > > > <div>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ________///&nbsp;&nbsp; \_/&nbsp;
> > > > > > \________/&nbsp; \&nbsp; ____</div>
> > > > > >
> > > > > <div><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</x-tab><x-tab>&
> > > > > nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</x-tab><x-tab>&nbsp;&nbsp;&n
> > > > > bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</x-tab><x-tab>&nbsp;&nbsp;&nbsp;&nbsp;&nb
> > > > > sp;&nbsp;&nbsp;&nbsp;</x-tab>&nbsp;
> > > > > > \/</div>
> > > > > > <div>Manager Signal Integrity, Enterprise Line of Business</div>
> > > > > > <div>408-527-9186,&nbsp; Page 408-308-5501, Fax 408-526-5504,&nbsp;
> > > > > > N6PFN</div>
> > > > > > *********************************************************************
> > > > > > </html>
> > > > > >
> > > > > >
> > > > > > **** To unsubscribe from si-list or si-list-digest: send e-mail to
> > > > > > majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE
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> > > > > > ****
> > > > > >
> > > > > > ------------------------------>
> > > > > >
> > > > > > End of si-list-digest V1 #286
> > > > > > ****> *************************
> > > > > >
> > > > > >
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>
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-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Mike Jenkins               Phone: 408.433.7901            _____     
 LSI Logic Corp, ms/G715      Fax: 408.433.7461        LSI|LOGIC| (R)   
 1525 McCarthy Blvd.       mailto:Jenkins@LSIL.com        |     |     
 Milpitas, CA  95035         http://www.lsilogic.com      |_____|    
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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