General Pcb Routing Guidelines; Figure 15-1. Gssg Stack-Up - Nvidia Jetson TX2 NX Manual

Max Trace Lengths/Delays

Trace lengths/delays should include the carrier board PCB routing (where the Jetson TX2
NX mating connector resides) and any additional routing on a Flex/ secondary PCB
segment connected to main PCB. The max length/delay should be from Jetson TX2 NX to
the actual connector (i.e. USB, HDMI, etc.) or device (i.e. onboard USB device, Display
driver IC, camera imager IC, etc.)
Trace Delay/Flight Time Matching

Signal flight time is the time it takes for a signal to propagate from one end (driver) to the
other end (receiver). One way to get same flight time for signal within signal group is to
match trace lengths within specified delay in the signal group.
Total trace delay = Carrier PCB trace delay only. Do not exceed maximum trace delay
•
specified.
For six layers or more, it is recommended to match trace delays based on flight time of
•
signals. For example, outer-layer signal velocity could be 150psi (ps/inch) and inner-
layer 180psi. If one signal is routed 10 inches on outer layer and second signal is
routed 10 inches in inner layer, difference in flight time between two signals will be
300psi. That is a big difference if required matching is 15ps (trace delay matching). To
fix this, inner trace needs to be 1.7 inches shorter or outer trace needs to be 2 inches
longer.
In this design guide, terms such as intra-pair and inter-pair are used when describing
•
differential pair delays. Intra-pair refers to matching traces within differential pair (for
example, true to complement trace matching). Inter-pair matching refers to matching
differential pairs average delays to other differential pair average delays.
15.5

General PCB Routing Guidelines

For GSSG stack-up to minimize crosstalk, signal should be routed in such a way that they are
not on top of each other in two routing layers (see Figure 15-1).
Figure 15-1. GSSG Stack-Up
G
S
S
G
Do not route other signals or power traces/areas directly under or over critical high-speed
interface signals.
Note: The requirements detailed in the interface signal routing requirements tables must be met
for all interfaces implemented or proper operation cannot be guaranteed.
NVIDIA Jetson TX2 NX
General Routing Guidelines
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