Datasheet

SCBA015A
7–10
Fast GTLP Backplanes With the GTLPH1655
Z
O
+
LȀ
CȀ
Ǹ
t + LȀ CȀ
Ǹ
Where:
Z
O
= impedance of the line (Ω)
τ = propagation delay of the line (ns/m)
L′ = inductive component of the line (nH/cm)
C′ = capacitive component of the line (pF/cm)
Table 2. Typical Characteristic Properties of Lines
L′
(nH/cm)
C′
(pF/cm)
Z
O
(Ω)
τ
(ns/m)
Point-to-point line between two components 5 to 10 0.5 to 1.5 70 to 100 ≈5
Bus line 5 to 10 10 to 30 20 to 40 10 to 20
If a signal edge is fed into the beginning of the line (see Figure 4), a signal amplitude is created
that can be calculated from the simple voltage divider, consisting of the internal resistance of the
signal generator and the impedance of the line (Equation 3). The termination resistor R
TT
has no
influence on the edge because, at this point, the edge changes the voltage only at the beginning
of the line, and at the end of the line no voltage change occurs.
U
i
+ U
G
Z
O
Z
O
) R
G
Where:
U
i
= amplitude of the incident wave (V)
U
G
= open-circuit voltage of the signal generator (V)
R
G
= output resistance of the signal generator (Ω)
Z
O
= impedance of the line (Ω)
U
i
l
U
G
R
TT
Z
O
R
G
U
r
Figure 4. Wavefronts on Lines
(1)
(2)
(3)