Advantech SOM-ETX Design Guide
5.5.3 Layout Guideline
5.5.3.1 RLC Components
The RGB outputs are current sources and therefore require 75-ohm load resistors
from each RGB line to analog ground to create the output voltage (approximately 0 to
0.7 volts). These resistors should be placed near the VGA port (a 15-pin D-SUB
connector). Serial ferrite beads for the RGB lines should have high frequency
characteristics to eliminate relative noise. The 33-ohm series damping resistors for
HSY and VSY should be placed near the D-SUB connector.
SOM-ETX
R
G
A
A
27p
bead
bead
bead
Route to Minimum
B
A
27p
27p
27p 27p 27p
75ohm
HSV
VSV
A
A
68p
68p
33ohm
33ohm
D-Sub15
Route to Minimum
Figure 5-16 VGA Layout Guidelines
5.5.3.2 RGB Output Current Balance Path
Analog R, G and B (red, green and blue) traces should be designed to be as short as
possible. Careful design, however, will allow considerable trace lengths with no
visible artifacts. GNDRGB is an "analog current balance path" for the RGB lines. In
terms of layout, GNDRGB should follow 2 traces that encapsulate the RGB traces all
the way to the D-shell connector (VGA Port) and should not be tied to ground until
connected to the Right Angle D-type connector.
SOM-ETX
R
VGA Connector
G
B
D-Sub15
RLC
12 mils wide
15~30 mils wide
RGBGND
RGBGND
"
。
" :ground via on RGBGND balance path
Figure 5-17 RGB Output Layout Guidelines
80
Chapter 5 Carrier Board Design Guidelines
