From: abe riazi ([email protected])
Date: Mon Apr 23 2001 - 18:59:21 PDT
Dave Instone Wrote:
"how long does the transmission line
have to be to be recognised ,by the signal, as a transmission line?"
The Critical Length (Lc) offers useful guideline for answering above question. It is given by:
Lc = k(Tr)/(Tpd)
Where, Tr is rise time and Tpd is signal propagation delay.
A good value for coefficient k is 1/6; and assuming FR-4 substrate typical delays for outer and inner layers include:
Tpd = 150 ps/in (Microstrip),
Tpd = 180 ps/in (Stripline)
After critical line length is calculated, the trace segments smaller than Lc can be classified as lumped and those exceeding Lc as distributed.
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