Datasheet

SCBA015A
7–11
Fast GTLP Backplanes With the GTLPH1655
This voltage edge now runs from the beginning of the line to the end. This first wave is called the
incident wave. When the voltage wave reaches the end of the line, a reflected voltage wave is
generated, the amplitude of which can be calculated from the reflection factor ρ, as shown in
Equations 4 and 5.
ò 
R
TT
 Z
O
R
TT
 Z
O
U
r
 U
i
 ò
Where:
U
r
= amplitude of the reflected wave (V)
U
i
= amplitude of the incident wave (V)
ρ = reflection factor
R
TT
= termination resistor at the end of the line (Ω)
Z
O
= impedance of the line (Ω)
Using Equations 3, 4, and 5, results at the end of the line can be predicted:
R
TT
= 0 ⇒ ρ = –1 (see Figure 5a)
The incident wave is inverted and reflected at the end of the line. Incident and reflected
waves therefore cancel out each other, and there is no voltage increase at the end of the
line.
R
TT
= Z
O
⇒ ρ = 0 (see Figure 5b)
No line reflections occur. The end of the line is perfectly terminated.
R
TT
= ∞ ⇒ ρ = +1 (see Figure 5c)
The incident wave is fully reflected at the end of the line. There is a doubling of the amplitude
at the end of the line.
A detailed analysis follows in
End of the Line: The Reflected Wave .
(4)
(5)