Dc Blocking Capacitor; Emi Design Consideration - Intel EP80579 Manual

Figure 20. Routing Examples of the Length Compensation #2
5.4.5

DC Blocking Capacitor

Many differential signals require DC blocking capacitors. In these cases, placement
symmetry for the capacitors is recommended, as shown in
Figure 21. DC Blocking Capacitor
5.5

EMI Design Consideration

As microprocessor power and speeds increase, the ability to contain the corresponding
electromagnetic radiation becomes more difficult. Frequencies generated by these
processors may be in the low GHz range, which may impact both the system design
and the EMI test methodology.
This section provides electrical and mechanical design engineers with information to aid
in developing a platform that may meet government EMI regulations. Specifically, the
impact of differential clocking, spread spectrum clocking, and the test methodology to
the FCC Class B requirements are discussed.
Designers must be aware that implementing all the recommendations in this guideline
may not ensure compliance to EMI regulations. Rather, these guidelines may help to
reduce the emissions from processors and motherboards and make chassis design
easier.
The following sections describe design techniques that may be applied to minimize EMI
emissions. Some techniques have been incorporated into Intel-enabled designs
(differential clock drivers, selective clock gating, etc.), while others must be
implemented by motherboard designers (trace routing, clocking schemes, etc.).
®
Intel EP80579 Integrated Processor Product Line
Platform Design Guide
48
®
Intel EP80579 Integrated Processor Product Line—High-Speed Design Concerns
≥
600 mils
<
600 mils
No Length Compensation is Required
<
600
≥
600 mils
<
600 mils
Length Compensation is Required
Figure
mils
21.
May 2010
Order Number: 320068-005US