82541PI(ER) and 82562GZ(GX) Dual Footprint LOM Design Guide
Application Note (AP-468)
5
2.0
Frequency Control Device Design Considerations
This section provides information regarding frequency control devices, including crystals and
oscillators, for use with all Intel® Ethernet controllers. Several suitable frequency control devices
are available; none of which present any unusual challenges in selection. The concepts documented
herein are applicable to other data communication circuits, including Physical Layer devices
(PHYs).
The Intel® Ethernet controllers contain amplifiers which, when used with the specific external
components, form the basis for feedback oscillators. These oscillator circuits, which are both
economical and reliable, are described in more detail in
“Crystal Selection Parameters”
The Intel® Ethernet controllers also have bus clock input functionality, however a discussion of
this feature is beyond the scope of this document, and will not be addressed.
The chosen frequency control device vendor should be consulted early in the design cycle. Crystal
and oscillator manufacturers familiar with networking equipment clock requirements may provide
assistance in selecting an optimum, low-cost solution.
2.1
Frequency Control Component Types
Several types of third-party frequency reference components are currently marketed. A discussion
of each follows, listed in preferred order.
2.2
Quartz Crystal
Quartz crystals are generally considered to be the mainstay of frequency control components due to
their low cost and ease of implementation. They are available from numerous vendors in many
package types and with various specification options (see
Table 4. Recommended Crystals
Manufacturer
Part Number
Raltron
AS-25.000-20-F-SMD-T
Citizen America Corp
HCM4925.000MBBKTR
NDK America Inc
41CD25.0S11005020
TXC Corporation - USA
6C25000131
