Reference Schematic; Layout Consideration; Figure 29 Tv-Out Reference Schematic - Emerson COM Express Carrier Design Manual

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14.2 Reference Schematic

Figure 28 TV-Out Reference Schematic

All signals along the left edge of the figure are sourced directly from the COM Express module. No

additional pull-ups or terminations beyond what is shown in the figure are required. The 150 ohm

termination to ground is important both for signal integrity and to establish the correct DC level on the

line. All components shown in this figure should be placed close to the carrier board connector shown

in the figure.

Each of the TV-DAC channels should have a 150 ohm ±1% pull-down termination resistor connected

from the TV-DAC output of the COM Express module to the carrier board ground. This termination

resistor should be placed as close as possible to the TV-Out connector on the carrier board. A second

150 ohm ±1% termination resistor exists on the COM Express module itself.

At least 30 mils of spacing should be used for the routing between each TV-DAC channel to prevent

crosstalk between the TV-DAC signals. The maximum trace length distance of the TV-DAC signals

between the COM Express connector and the 150 ohm ±1% termination resistor should be within 12

inches. This distance should be routed with a trace impedance of 50 ohms.

There should be a PI-filter placed on each TV-DAC channel output to reduce high-frequency noise and

EMI. The PI-filter consists of two 10pF capacitors with a 120 ohm at 30 Mhz ferrite bead between them.

It is recommended to place the PI-filters and the termination resistors as close as possible to the TV-

Out connector on the carrier board. The PI-filters should be separated from each other by at least

50 mils or more in order to minimize crosstalk between the TV-DAC channels.

COM Express Carrier Type 2

Design Guide

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