Intel 820E Benutzerhandbuch

Design Guide 

 

117 

 

Intel® 
82562ET /

 

82562EM

B

 

A

 

ICH2

 

EEPROM

 

Magnetics

 

Module

Line

RJ45

 

crit_dim_comp_plac

 

 

A 1 

<1 

inch 

B 2 

<1 

inch 

Distance ‘A,’ in the previous figure, should be given the highest priority during board layout. The 
separation between the magnetics module and the RJ45 connector should be kept to less than 1 inch. The 
following trace characteristics are important and should be observed: 

• 

Differential impedance: The differential impedance should be 100 

Ω

. The single-ended trace 

impedance is approximately 50 

Ω

. However, the differential impedance also can be affected by the 

spacing between traces. 

• 

Trace symmetry: Differential pairs (e.g., TDP and TDN) should be routed with consistent separation 
and with exactly the same lengths and physical dimensions (e.g., width). 

Caution:  Asymmetric and unequal-length traces in the differential pairs contribute to common-mode noise. This 

can degrade the receive circuit’s performance and contribute to radiated emissions from the transmit 
circuit. If the Intel

 

82562ET component must be placed farther than a couple of inches from the RJ45 

connector, distance B can be sacrificed. It should be a priority to minimize the total distance between the 
Intel

 

82562ET component and RJ-45. 

Note:  The measured trace impedance for layout designs targeting 100 

Ω

 often yields a lower actual impedance. 

OEMs should verify the actual trace impedance and adjust their layout accordingly. If the actual 

impedance is consistently low, a target of 105 

Ω

–110 

Ω

 should compensate for second-order effects.