The model below corresponds most closely to a lossy transmission line
driven by a voltage source and open circuited at the output end.
0--/\/\/\---() () ()------+---------0
Vin () () | Vout
Being an open-circuited t-line, you fully expect a reflection
coefficient of 1 at the open end, (and -1 at the source end) and hence
big oscillations with a period determined by the sqrt(LC) time
constant. The effect of adding the series R is to damp these
oscillations--essentially changing from a lossless (crude) t-line
model to a lossy (crude) one. But the oscillations will still be
there--at least until you make the resistance larger than 2*sqrt(L/C),
at which point the circuit becomes more like a distributed RC
transmission line (familiar to people who deal with on-chip
interconnects) than the LC ones that PCB designers know and love.
-- J. Eric Bracken, Ph.D. Tel: 1.412.261.3200 x135 Group Leader, Signal Integrity R&D Fax: 1.412.471.9427 Ansoft Corp., Four Station Square, Suite 660 firstname.lastname@example.org Pittsburgh, PA USA 15219-1119 http://www.ansoft.com
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