[SI-LIST] Re: When a signal is considered high speed signal
- From: wolfgang.maichen@xxxxxxxxxxxx
- To: Rama Mohan Reddy Boreddy <mohan.svuce@xxxxxxxxxxxxxx>
- Date: Mon, 21 Sep 2009 09:15:36 -0700
In time domain, the critical factor is the ratio between signal rise time
(NOT the clock frequency or data rate) and the path propagation delay.
Basically, the moment the path delay approaches some fraction of the
signal rise time, you will see transient effects (reflections etc.) and
you can no longer consider the whole structure as lumped.
There isn't a generally valid number for that critical ratio, as it
depends on numerous factors, e.g. your system's tolerance for waveform
aberrations, your accuracy requirements, the size and location of
discontinuities, but the typical range is about from 1:3 to 1:20. E.g. for
accurate simulations you may want to make sure that none of the lumped
components in your simulation produces delay exceeding 1/20th of your
signal rise time, but if all that you are after is avoidance of severe
waveform distortion but not much more you may get away with stubs in your
path that are up to 1/4th of your rise time.
In the frequency domain the wavelength of the highest frequency of
interest takes the place of the rise time. E.g. most frequency domain
simulation tools will at least issue a warning if your cell size exceeds
1/20th of that wavelengths.
Wolfgang
Rama Mohan Reddy Boreddy <mohan.svuce@xxxxxxxxxxxxxx>
Sent by: si-list-bounce@xxxxxxxxxxxxx
09/20/2009 11:52 PM
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[SI-LIST] When a signal is considered high speed signal
Hi,
Can anyone tell when a signal is considered as a high speed signal? Is
there any definition for high speed signal in time domain and frequency
domain?
I know that a rise time and PCB trace/Interconnect legth is one of the
parameters to define a signal as high speed signal. Can any body provide
me
the formula
Can any body share a FAQ on high speed signals and Cross talk
Regards,
Rama Mohan Reddy
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