Light Emitting Diodes; Vibrational Mode; Nominal Frequency; Frequency Tolerance - Intel Quark SoC X1000 Design Manual

LAN Design Considerations and Guidelines—Intel
21.16

Light Emitting Diodes

The device has three high-current outputs to directly drive LEDs for link, activity and
speed indication. Since LEDs are likely to be integral to a magnetics module, take care
to route the LED traces away from potential sources of EMI noise. In some cases, it
may be desirable to attach filter capacitors.
LAN LED traces should be placed at least 6x (side by side separation) the dielectric
height from sources of noise (ex: signaling traces) and susceptible signal traces (ex:
reset signals) on the same or adjacent layers.
LAN LED traces should be placed at least 7x (broadside coupling) the dielectric height
from sources of noise (ex: signaling traces) and susceptible signal traces (ex: reset
signals) on the same or adjacent layers.
21.17

Vibrational Mode

Crystals in the frequency range referenced above are available in both fundamental and
third overtone. Unless there is a special need for third overtone, fundamental mode
crystals should be used.
21.18

Nominal Frequency

The Ethernet controller uses a crystal frequency of 50.000 MHz. The 50 MHz input is
used to generate a 125 MHz transmit clock for 100BASE-TX operation, and 10 MHz and
20 MHz transmit clocks, for 10BASE-T operation.
21.19

Frequency Tolerance

The frequency tolerance for an Ethernet Platform LAN Connect device is dictated by the
IEEE 802.3 specification as ±50 parts per million (ppm). This measurement is
referenced to a standard temperature of 25 °C.
21.20

Troubleshooting Common Physical Layout Issues

The following is a list of common physical layer design and layout mistakes in LAN on
Motherboard (LOM) designs.
1. Lack of symmetry between the two traces within a differential pair. Asymmetry can
create common-mode noise and distort the waveforms. For each component and
via that one trace encounters, the other trace should encounter the same
component or a via at the same distance from the Ethernet silicon.
2. Unequal length of the two traces within a differential pair. Inequalities create
common-mode noise and will distort the transmit or receive waveforms.
3. Excessive distance between the Ethernet silicon and the magnetics. Long traces on
FR4 fiberglass epoxy substrate will attenuate the analog signals. In addition, any
impedance mismatch in the traces will be aggravated if they are longer than the
four-inch guideline.
4. Routing any other trace parallel to and close to one of the differential traces.
Crosstalk getting onto the receive channel will cause degraded long cable BER.
Crosstalk getting onto the transmit channel can cause excessive EMI emissions and
can cause poor transmit BER on long cables. At a minimum, for stripline other
signals should be kept at least 6x the height of the thinnest adjacent dielectric
layer. For microsrip it is 7x. The only possible exceptions are in the vicinities where
the traces enter or exit the magnetics, the RJ-45 connector, and the Ethernet
silicon.
June 2014
Order Number: 330258-002US
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Quark™ SoC X1000
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Intel Quark™ SoC X1000
PDG
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