[SI-LIST] Re: Insertion Loss of Passive Components

All-

Thanks for your insight.  I resolved the issue.  To those who are 
interested, the differential trace model included one trace that was 
approximately 170mils longer than the other trace.  The connector 
launch, due to its geometry, had that same trace 170mils shorter than 
the other trace.  So when I measured differential insertion loss, 
there was a resonance due to the length mismatch on both of the 
subcircuits.  However, they pieced together and the resonance was 
removed, causing improved insertion loss.

John - I like your filter analogy, but I believe that the analogy 
breaks down when we become concerned about transmission lines (and EM 
waves) and not lumped elements.  It does little to feed our intuition 
as to how an electromagnetic wave travels down a trace.  It is an 
analog world, but it's also an electromagnetic world:)

--- In si-list@xxxxxxxxxxxxxxx, "Hill, John" <John.Hill@...> wrote:
>
> Ryan,
> 
> 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 
the
> impedance.
> 
> Now consider the same filter in the stop band. The inductors and
> capacitances do not resonate together and either changes the real 
value
> of the filter or makes it very non-real.=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 
filter
> deliberately miss-matches the impedances.=3D20
> 
> Look at your circuit as a filter. Is it matching or miss-matching 
the
> source to the load? Remember digital signal are wide band signals. 
We
> typically need to design our signal paths as low pass filters with 
high
> cutoff frequencies.
> 
> As we all know, it is an analog world.
> 
> Best regards,
> 
> John
> 
> 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
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> -----Original Message-----
> 
> 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
> 
> SI-Listers:
> 
> I have set up a simulation and am very confused by the results.  
I=3D20
> have a differential trace in series with a connector launch.
> 
> I am getting very strange insertion loss results so I'm hoping=3D20
> somebody could help advise me as to whether my model is wrong, or 
I=3D20
> am wrong.
> 
> When I view the differential insertion loss of the system (both=3D20
> subcircuits in series), the loss is better (there is less loss) 
than=3D20
> the differential insertion of the trace only.  Is this possible?  
I=3D20
> always thought that it was impossible to improve the insertion 
loss=3D20
> by adding a passive component.  And I think I still believe that, 
but=3D20
> now I'm getting a little confused.
> 
> It's also important to note that the single-ended insertion loss=3D20
> results seem to be as expected.  That is, the insertion loss of 
the=3D20
> system is worse than the insertion loss of either individual=3D20
> component.
> 
> Is something occurring with the differential signal to allow it 
to=3D20
> perform better?
> 
> Please advise.  Thanks in advance for your response.
> 
> Ryan Satrom
> Everett Charles Technologies
> ryan.satrom@...
> 
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