Jetson AGX Xavier Series Product
DG-09840-001_v2.5 | 131
Chapter 21.
Transmission Line Primer
21.1
Basic Board Level Transmission Line
Theory
NVIDIA maintains strict guidelines for high-frequency PCB transmission lines to ensure
optimal signal integrity for data transmission. This section provides a brief primer into basic
board-level transmission line theory.
21.1.1
Characteristics
The most important PCB transmission line characteristics are listed in the following bullets:
Trace width/height, PCB height and dielectric constant, and layer stack-up affect the
characteristic trace impedance of a transmission line.
Z
0
=
L
C
˜
1/2
Signal rise time is proportional to the transmission line impedance and load capacitance.
*
C
Load
RiseTime
=
Z
0
*
R
Term
Z
0
+ R
Term
˜
Real transmission lines (Figure 21-1) have non-zero resistances that lead to attenuation
and distortion, creating signal integrity issues.
Figure 21-1. Typical Transmission Lin Circuit
Transmission Line
Z
S
Z
0
Z
L
Load
Source
Transmission lines are used to “transmit” the source signal to the load or destination with as
little signal degradation or reflection as possible. For this reason, it is important to design the
high-speed signal transmission line to fall within characteristic guidelines based on the signal
speed and type.
