NVIDIA Jetson TX2/TX2i OEM Product Design Guide
JETSON TX2/TX2i OEM PRODUCT | DESIGN GUIDE | 20180618
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Figure 52. Stripline Transmission Line
W
T
B
Z
0
=
ln
60
Er
4H
0.67
π
W 0.8 +
H
T
W
▪
Z
0
: Impedance
▪
W: Trace w idth (inches)
▪
T: Trace thickness (inches)
▪
Er: Dielectric constant of substrate
▪
H: Distance betw een signal and reference plane
18.3 Driver Characteristics
Driver characteristics are important to the integrity and maximum speed of the signal. The follow ing points identify key driv er
equations and concepts used to improve signal integrity and transmission speed.
▪
The driver (source) has resistive output impedance Z
S
, w hich causes only a fraction of the signal voltage to
propagate dow n the transmission line to the receiver (load).
-
• Transfer function at source:
T1
=
Z
0
Z
S
+ Z
0
-
• Driver strength is inversely proportional to the source impedance, Z
S
.
▪
Z
S
also acts as the source termination, w hich helps dampen reflection.
-
Source reflection coefficient:
R1
=
(Z
S
–
Z
0
)
(Z
S
+ Z
0
)
18.4 Receiver Characteristics
Receiver characteristics are important to the integrity and detectability of the signal. The follow ing points identify key receiver
concepts and equations for optimum signal integrity at the final destination.
▪
The receiver acts as a capacitive load and often has a high load impedance, Z
L
.
▪
Unterminated transmission lines cause overshoot and reflection at the receiver, w hich can cause data corruption.
-
Output transfer function at load:
T2
=
2
*
Z
L
Z
L +
Z
0
-
Load reflection coefficient:
R2
=
(Z
L
–
Z
0
)
(Z
L
+ Z
0
)
▪
Load impedance can be low ered w ith a termination resistor (R
Term
) placed at the end of the transmission line.
-
Reflection is minimized w hen Z
L
matches Z
0
18.5 Transmission Lines & Reference Planes
Defining an appropriate reference plane is vital to transmission line performance due to crosstalk and EMI issues. The follow ing
points explore appropriate reference plane identification and characteristics for optimal signal integrity:
▪
Transmission line return current (Figure 53)
-
High-speed return current follow s the path of least inductance.
-
The low est inductance path for a transmission line is right underneath the transmission line; i(D) is
proportional to:
