[SI-LIST] Re: No need of termination within critical length??
- From: dbrooks9@xxxxxxxxxxxxxxx
- To: "Sonu Kurian N.D" <sonukurian@xxxxxxxxxxxxxxx>
- Date: Thu, 17 Sep 2009 08:41:32 -0700
Clearly, if the trace is very short, no termination is required. If th= e
trace is very long, a termination is probably required. So where is the p=
oint at which we crossover from no termination being required to where a te=
rmination is required? That point is not a precise point. We all may make s=
lightly different judgments about this, depending on our preferences and th=
e characteristics (and sensitivities) of our circuits. However, that point =
is generally around the so-called critical length. Shorter than that we *pr=
obably* don't need a termination, longer than that we *probably* do need a =
termination.
For *short* traces, the signal levels (and reflections)= stabilize before we
sample the signal level. They stabilize through some c= ombination of
*time*,impedance-driven voltage-divider actions, and driver = *swamping*.
For*long* traces, we sample the signal levels before the signa= l levels
(reflections) stabilize. So, for long traces, we need to control t= hose
reflections. For short traces we do not.
Doug Brooks
http://www.ultracad.com[1]
-------- Original Message --------
Subject: [SI-LIST] No need of termination within critical length??
From: "Sonu Kurian N.D" <sonukurian@xxxxxxxxxxxxxxx>
Date: Wed, September 16, 2009 11:57 pm
To: si-list@xxxxxxxxxxxxx
Hi All,
I am puzzled about why termination is not required if trace length is less
than critical length.
I read like if a driver encounters a reflected signal when it is
rising(driving) , its able to absorb reflection.Is it so?
Or is the situation like ..the reflections will be there..but the Setup
condition can be met..so we need not worry..??
Can anyone please throw some light on this..
Many thanks,
Sonu
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