[SI-LIST] Re: Insertion Loss of Passive Components
- From: istvan novak <Istvan.Novak@xxxxxxx>
- To: hreidmarkailen@xxxxxxxxx
- Date: Sun, 17 Dec 2006 10:37:38 -0500
Agathon,
It is true that for electrically short structures there is no need for
distributed model. However,
the 170-mil length difference is long enough that when measured up to 20
or 40GHz, the
time-of-flight difference in the two legs shows up as a cancellation (or
resonance). With
regular FR4, the 'resonance' could be around 15GHz. There was a paper on
this effect
at DesignCon 2006: Stephen B. Smith, “Theory and Measurement of Unbalanced
Differential-Mode Transmission Lines”, and more papers will show up at
DesignCon 2007.
Regards,
Istvan Novak
SUN Microsystems
agathon wrote:
>Ryan,
>I would submit that it really ought to help. And, sorry, but please don't
>claim that for SI Engineers in general. :-)
>All the laws of physics rule, not just some.
>The net IS a filter. And, if the section (170mil) is electrically short,
>then lumped "filter" modeling could be a perfectly appropriate way to
>understand and accurately model its interaction with the rest of the net.
>It is a well known technique in any college microwave advanced text. In
>that case, the "propagation" is irrelevant and, if resonance is at work, the
>variable t, for time, itself is irrelevant. So, time to understand
>filters.
>
>On the other hand, I didn't read any convincing explanation of a "resonance"
>on a bare diff pair with mismatched conductor lengths. Most likely, the
>higher loss of the pair was due to mode conversion due to the mismatch,
>fixed mostly by the adjustment presented by the connector lead lengths,
>which WOULD be simply a correction of unequal flight times -- most easily
>viewed as a propagation issue; ie: time domain.
>
>
>On 12/13/06, ryansatrom <ryan.satrom@xxxxxxxxxxx> wrote:
>
>
>>John-
>>
>>You are correct. As an SI Engineer, it doesn't help my understanding
>>to view a net as a filter. But that doesn't make it invalid.
>>
>>Thanks for the insight.
>>
>>Ryan Satrom
>>
>>
>>--- In si-list@xxxxxxxxxxxxxxx, "Hill, John" <John.Hill@...> wrote:
>>
>>
>>>Ryan,
>>>
>>>I would summit to you that not all filters use lumped elements.
>>>
>>>
>>Strip
>>
>>
>>>line filters are just lengths of coupled transmission lines and they
>>>make very good microware filters.=3D20
>>>
>>>You can also consider a length of coupled transmission lines as two
>>>transmission lines with crosstalk. The vantage point depends a lot
>>>
>>>
>>on if
>>
>>
>>>you are an SI engineer or an RF engineer.=3D20
>>>
>>>Best regards,
>>>
>>>John =3D20
>>>
>>>John Hill
>>>Design Engineer
>>>TK HOLDINGS INC =3D20
>>>Electronics=3D20
>>>27200 Haggerty Road Suite B-12 =3D20
>>>Farmington Hills, MI 48331
>>>Office Phone: 248 699 2915
>>>Mobile Phone 248 765 3599
>>>
>>>
>>>
>>>=3D20
>>>
>>>---------------------------------------
>>>The information in this email and attachments hereto may contain
>>>
>>>
>>legally =3D
>>
>>
>>>privileged, proprietary or confidential information that is
>>>
>>>
>>intended for =3D
>>
>>
>>>a particular recipient. If you are not the intended recipient(s),
>>>
>>>
>>or the =3D
>>
>>
>>>employee or agent responsible for delivery of this message to the =3D
>>>intended recipient(s), you are hereby notified that any disclosure,
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>>=3D
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>>>copying, distribution, retention or use of the contents of this e-
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>>>
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>>Takata =3D
>>
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>>>customers or vendors, any information contained in this e-mail is =3D
>>>subject to the terms and conditions in the governing contract, if =3D
>>>applicable. If you have received this communication in error,
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>>
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>>>electronic copies of this communication and destroy any paper
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>>
>>>---------------------------------------
>>>-----Original Message-----
>>>
>>>From: si-list-bounce@... [mailto:si-list-bounce@...]
>>>On Behalf Of ryansatrom
>>>Sent: Wednesday, December 13, 2006 10:50 AM
>>>To: si-list@...
>>>Subject: [SI-LIST] Re: Insertion Loss of Passive Components
>>>
>>>All-
>>>
>>>Thanks for your insight. I resolved the issue. To those who are=3D20
>>>interested, the differential trace model included one trace that
>>>
>>>
>>was=3D20
>>
>>
>>>approximately 170mils longer than the other trace. The connector=3D20
>>>launch, due to its geometry, had that same trace 170mils shorter
>>>
>>>
>>than=3D20
>>
>>
>>>the other trace. So when I measured differential insertion loss,=3D20
>>>there was a resonance due to the length mismatch on both of the=3D20
>>>subcircuits. However, they pieced together and the resonance was=3D20
>>>removed, causing improved insertion loss.
>>>
>>>John - I like your filter analogy, but I believe that the analogy=3D20
>>>breaks down when we become concerned about transmission lines (and
>>>
>>>
>>EM=3D20
>>
>>
>>>waves) and not lumped elements. It does little to feed our
>>>
>>>
>>intuition=3D20
>>
>>
>>>as to how an electromagnetic wave travels down a trace. It is an=3D20
>>>analog world, but it's also an electromagnetic world:)
>>>
>>>--- In si-list@xxxxxxxxxxxxxxx, "Hill, John" <John.Hill@> wrote:
>>>
>>>
>>>>Ryan,
>>>>=3D20
>>>>Consider a filter, in the pass band the filter can have a lot of
>>>>inductors and capacitors between the source and the load, but the
>>>>insertion loss is low. This is because all of the inductances and
>>>>capacitances resonate together without changing the real value
>>>>
>>>>
>>of=3D20
>>
>>
>>>the
>>>
>>>
>>>>impedance.
>>>>=3D20
>>>>Now consider the same filter in the stop band. The inductors and
>>>>capacitances do not resonate together and either changes the
>>>>
>>>>
>>real=3D20
>>
>>
>>>value
>>>
>>>
>>>>of the filter or makes it very non-real.=3D3D3D20
>>>>=3D20
>>>>The point is that in the pass band the filter correctly matches
>>>>
>>>>
>>the
>>
>>
>>>>source impedance to the load impedance and in the stop band the=3D20
>>>>
>>>>
>>>filter
>>>
>>>
>>>>deliberately miss-matches the impedances.=3D3D3D20
>>>>=3D20
>>>>Look at your circuit as a filter. Is it matching or miss-
>>>>
>>>>
>>matching=3D20
>>
>>
>>>the
>>>
>>>
>>>>source to the load? Remember digital signal are wide band
>>>>
>>>>
>>signals.=3D20
>>
>>
>>>We
>>>
>>>
>>>>typically need to design our signal paths as low pass filters
>>>>
>>>>
>>with=3D20
>>
>>
>>>high
>>>
>>>
>>>>cutoff frequencies.
>>>>=3D20
>>>>As we all know, it is an analog world.
>>>>=3D20
>>>>Best regards,
>>>>=3D20
>>>>John
>>>>=3D20
>>>>John Hill
>>>>Design Engineer
>>>>TK HOLDINGS INC =3D3D3D20
>>>>Electronics=3D3D3D20
>>>>27200 Haggerty Road Suite B-12 =3D3D3D20
>>>>Farmington Hills, MI 48331
>>>>Office Phone: 248 699 2915
>>>>Mobile Phone 248 765 3599
>>>>=3D20
>>>>=3D20
>>>>=3D3D3D20
>>>>=3D20
>>>>---------------------------------------
>>>>The information in this email and attachments hereto may
>>>>
>>>>
>>contain=3D20
>>
>>
>>>legally =3D3D3D
>>>
>>>
>>>>privileged, proprietary or confidential information that is=3D20
>>>>
>>>>
>>>intended for =3D3D3D
>>>
>>>
>>>>a particular recipient. If you are not the intended recipient
>>>>
>>>>
>>(s),=3D20
>>
>>
>>>or the =3D3D3D
>>>
>>>
>>>>employee or agent responsible for delivery of this message to the
>>>>
>>>>
>>=3D
>>
>>
>>>=3D3D3D
>>>
>>>
>>>>intended recipient(s), you are hereby notified that any
>>>>
>>>>
>>disclosure,=3D20
>>
>>
>>>=3D3D3D
>>>
>>>
>>>>copying, distribution, retention or use of the contents of this e-
>>>>
>>>>
>>>mail =3D3D3D
>>>
>>>
>>>>information is prohibited and may be unlawful. When addressed
>>>>
>>>>
>>to=3D20
>>
>>
>>>Takata =3D3D3D
>>>
>>>
>>>>customers or vendors, any information contained in this e-mail is
>>>>
>>>>
>>=3D
>>
>>
>>>=3D3D3D
>>>
>>>
>>>>subject to the terms and conditions in the governing contract, if
>>>>
>>>>
>>=3D
>>
>>
>>>=3D3D3D
>>>
>>>
>>>>applicable. If you have received this communication in error,=3D20
>>>>
>>>>
>>>please =3D3D3D
>>>
>>>
>>>>immediately notify us by return e-mail, permanently delete any
>>>>
>>>>
>>=3D3D3D
>>
>>
>>>>electronic copies of this communication and destroy any paper=3D20
>>>>
>>>>
>>>copies.
>>>
>>>
>>>>---------------------------------------
>>>>-----Original Message-----
>>>>=3D20
>>>>From: si-list-bounce@ [mailto:si-list-bounce@]
>>>>On Behalf Of ryansatrom
>>>>Sent: Tuesday, December 12, 2006 3:49 PM
>>>>To: si-list@
>>>>Subject: [SI-LIST] Insertion Loss of Passive Components
>>>>=3D20
>>>>SI-Listers:
>>>>=3D20
>>>>I have set up a simulation and am very confused by the results.
>>>>
>>>>
>>=3D20
>>
>>
>>>I=3D3D3D20
>>>
>>>
>>>>have a differential trace in series with a connector launch.
>>>>=3D20
>>>>I am getting very strange insertion loss results so I'm
>>>>
>>>>
>>hoping=3D3D3D20
>>
>>
>>>>somebody could help advise me as to whether my model is wrong,
>>>>
>>>>
>>or=3D20
>>
>>
>>>I=3D3D3D20
>>>
>>>
>>>>am wrong.
>>>>=3D20
>>>>When I view the differential insertion loss of the system
>>>>
>>>>
>>(both=3D3D3D20
>>
>>
>>>>subcircuits in series), the loss is better (there is less loss)=3D20
>>>>
>>>>
>>>than=3D3D3D20
>>>
>>>
>>>>the differential insertion of the trace only. Is this possible?
>>>>
>>>>
>>=3D20
>>
>>
>>>I=3D3D3D20
>>>
>>>
>>>>always thought that it was impossible to improve the insertion=3D20
>>>>
>>>>
>>>loss=3D3D3D20
>>>
>>>
>>>>by adding a passive component. And I think I still believe
>>>>
>>>>
>>that,=3D20
>>
>>
>>>but=3D3D3D20
>>>
>>>
>>>>now I'm getting a little confused.
>>>>=3D20
>>>>It's also important to note that the single-ended insertion =3D
>>>>
>>>>
>>>loss=3D3D3D20
>>>
>>>
>>>>results seem to be as expected. That is, the insertion loss of=3D20
>>>>
>>>>
>>>the=3D3D3D20
>>>
>>>
>>>>system is worse than the insertion loss of either
>>>>
>>>>
>>individual=3D3D3D20
>>
>>
>>>>component.
>>>>=3D20
>>>>Is something occurring with the differential signal to allow it=3D20
>>>>
>>>>
>>>to=3D3D3D20
>>>
>>>
>>>>perform better?
>>>>=3D20
>>>>Please advise. Thanks in advance for your response.
>>>>=3D20
>>>>Ryan Satrom
>>>>Everett Charles Technologies
>>>>ryan.satrom@
>>>>=3D20
>>>>
>>>>
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