[SI-LIST] Re: Vp on serpentine
- From: "Haller, Robert" <rhaller@xxxxxxxxxx>
- To: "'Andrew.Ingraham@xxxxxxxxxx'" <Andrew.Ingraham@xxxxxxxxxx>,"'htmguy@xxxxxxxxx'" <htmguy@xxxxxxxxx>
- Date: Wed, 1 Aug 2001 13:14:31 -0400
Hans and Andy,
I did some testing of serpentine lines.
I ran SPICE simulations using field solved 2d models then
measured varying serpentine configurations. I examined
impedance and Propagation delay variations as a function of varying
spacing, and signal edge rate. I did not look at
differential lines, but can summarize the single ended results.
When transmission lines was serpentined 'close' to themselves the Velocity
of
propagation decreased (The lines got Faster). You might think of the signal
taking
a shortcut across the distributed self capacitance of the closely
serpentined lines.
You might think this is good, but the variability of prop velocity
increased.
I believe this is because the capacitive coupling varies based on geometry,
while usually the dielectric constant variations are only source of prop
delay variability
(for a specific rise time and frequency). It is a small effect but
important when doing source syncronous designs.
regards,
bob
-----Original Message-----
From: Ingraham, Andrew [mailto:Andrew.Ingraham@xxxxxxxxxx]
Sent: Wednesday, August 01, 2001 8:56 AM
To: 'htmguy@xxxxxxxxx'
Cc: 'si-list'
Subject: [SI-LIST] Re: Vp on serpentine
> When serpentining (new word?) differential lines what
> is the effective reduction of Vp for the length of the
> serpentine?
I'm no expert, but I thought I understood that the effective velocity of
propagation INCREASES slightly. Do you have other evidence?
I would expect that it depends on the geometry you use.
Don't know if or how it differs for differential lines....
Andy
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