Design Guide
51
Platform Clock Routing Guidelines
4.3
Clock Driver Power Delivery
Designers must take special care to provide a quiet VDDA supply to the Ref VDD, VDDA and the
48 MHz VDD. These VDDA signals are especially sensitive to switching noise induced by the
other VDDs on the clock chip. They are also sensitive to switching noise generated elsewhere in
the system such as the processor voltage regulator. It is recommended that a ground flood be placed
directly under the clock chip to provide a low impedance connection for the VSS pins. In addition,
power vias should be distributed evenly throughout the ground flood.
Note:
For all power connections to planes, decoupling capacitors, and vias, the maximum trace width
allowable and shortest possible lengths should be used to ensure lowest possible inductance.
4.4
EMI Constraints
Clocks are a significant contributor to EMI. The following recommendations can aid in EMI
reduction:
•
Maintain uniform spacing between the two halves of differential clocks.
•
Route clocks on physical layer adjacent to the VSS reference plane only.
•
Turn off all unused clocks.
Summary of Contents for Xeon
Page 24: ...Introduction 24 Design Guide This page is intentionally left blank ...
Page 30: ...Component Quadrant Layout 30 Design Guide This page is intentionally left blank ...
Page 52: ...Platform Clock Routing Guidelines 52 Design Guide This page is intentionally left blank ...
Page 66: ...System Bus Routing Guidelines 66 Design Guide This page is intentionally left blank ...
Page 118: ...Intel 82870P2 P64H2 118 Design Guide This page is intentionally left blank ...
Page 146: ...I O Controller Hub 146 Design Guide This page is intentionally left blank ...
Page 148: ...Debug Port 148 Design Guide This page is intentionally left blank ...
Page 210: ...Schematic Checklist 210 Design Guide This page is intentionally left blank ...
Page 220: ...Layout Checklist 220 Design Guide This page is intentionally left blank ...
Page 222: ...Schematics 222 Design Guide This page is intentionally left blank ...