Hi quantrix,
C and L are not only geometry dependent. Capacitance is also material dependent.
c/sqrt(er) is also not constant over frequency (at least not for most of the
PCB materials available).
The signal propagates inside the dielectric because the energy is in the field,
and field is ranging from trace to reference (GND). That’s why propagation
delay is material dependent and independent of the impedance.
BR
Gert
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-----Ursprüngliche Nachricht-----
Von: si-list-bounce@xxxxxxxxxxxxx <si-list-bounce@xxxxxxxxxxxxx> Im Auftrag von
qantrix
Gesendet: Dienstag, 2. März 2021 10:36
An: si-list@xxxxxxxxxxxxx
Betreff: [SI-LIST] Re: Transmission Line Propagation Delay: Characteristic
Impedance and Dielectric Material
qantrix <qantrix@xxxxxxxxx>
11:28 (2 минуты назад)
кому: si-list
I have question about relationship between them.
I just read some article and asked myself a question. here is equations stated
in article, that all of us familiar:
Zoÿrt(L/C)
tpdÿrt(L*C)
vÿtpdÿsqrt(L*C)
vÿqrt(Er)
so c/qrt(Er)ñ/sqrt(L*C)
L and C are geometry dependent and variable for different structures
c/qrt(Er) - material dependent and constant
how constant can be equal to variable? something is missing here.
when we design pcb we consider propagation delay only dependent by materials
but not impedance we design.