COM Express® Carrier Board Design Guide
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2.11.2 Routing Considerations
Route traces with a target impedance of 55Ω with a tolerance of ±15%. Pay attention to ground
return paths for the analog signals. Digital signals routed in the vicinity of the analog audio signals
should not cross the power plane split lines. The analog and digital signals are to be far from each
other. Partition the Carrier Board with all analog components grouped together in one area and
group all digital components in another area.
Keep digital signal traces far from the analog input and voltage reference pins. Give separate
analog and digital ground planes with the digital components over the digital ground plane, and the
analog components, like analog power regulators, over the analog ground plane. The split between
the planes must be at least 0.05 inch wide.
Route analog power and signal traces over the analog ground plane. Route digital power and
signal traces over the digital ground plane. Place bypassing and decoupling capacitors close to the
IC pins with wide traces to minimize impedance. Place the crystal or oscillator near the codec.
Do not fully isolate the analog/audio ground plane from the rest of the Carrier Board ground plane.
Give a single point (0.25 inch to 0.5 inch wide) where the analog/isolated ground plane connects to
the main ground plane. The split between the planes must be at least 0.05 inch wide.
Signals entering or leaving the analog area must cross the ground split in the area where the
analog ground is attached to the main Carrier Board ground. No signal should cross the split/gap
between the ground planes to prevent a ground loop that will increase EMI emissions and degrade
the signal quality.
Summary of Contents for ET976
Page 1: ...COM EXPRESS CARRIER BOARD DESIGN GUIDE Version 1 0 January 2022...
Page 11: ...COM Express Carrier Board Design Guide 5 Figure 3 PCI Express x4 Slot Example...
Page 12: ...6 COM Express Carrier Board Design Guide Figure 4 PCIe Mini Card Reference Circuitry...
Page 19: ...COM Express Carrier Board Design Guide 13 Figure 7 HDMI Example 1...
Page 20: ...14 COM Express Carrier Board Design Guide Figure 7 HDMI Example 2...
Page 21: ...COM Express Carrier Board Design Guide 15 Figure 8 DVI Example 1...
Page 22: ...16 COM Express Carrier Board Design Guide Figure 8 DVI Example 2...
Page 31: ...COM Express Carrier Board Design Guide 25 Figure 12 USB 3 0 Example 2...
Page 37: ...COM Express Carrier Board Design Guide 31 Figure 14 LVDS Reference Schematic 2...
Page 44: ...38 COM Express Carrier Board Design Guide Figure 16 VGA Reference Schematics 2...
Page 48: ...42 COM Express Carrier Board Design Guide Figure 18 HDA Example Schematic 2...
Page 52: ...46 COM Express Carrier Board Design Guide Figure 19 LPC Super I O Example 2...
Page 61: ...COM Express Carrier Board Design Guide 55 Figure 24 General Purpose Serial Port Example 2...
Page 70: ...64 COM Express Carrier Board Design Guide Figure 28 PWRBTN and SYS_RESET Circuitry...
Page 84: ...78 COM Express Carrier Board Design Guide Chapter 4 Carrier Board PCB Layout Guidelines...
