Intel Xeon Processor Multiprocessor Platform Design Guide

86
Processor Power Distribution Guidelines
The function of the filter is two-fold. It protects the PLL from external noise through low-pass
attenuation. It also protects the PLL from internal noise through high-pass filtering. In general, the
low-pass description forms an adequate description for the filter. For simplicity we are addressing
the recommendation for V
CCA
filter design. The same characteristics and design approach is
applicable for V
CCIOPLL
filter design.
The AC low-pass specification, with input at V
CC
and output measured across the capacitor, is as
follows:
• < 0.2 dB gain in pass band
• < 0.5 dB attenuation in pass band < 1 Hz (see DC drop in next set of requirements)
• 34 dB attenuation from 1 MHz to 66 MHz
• 28 dB attenuation from 66 MHz to core frequency
The filter specification (AC) is graphically shown in Figure 8-16.
Figure 8-15. Filter Topology
V
CC
V
CCA
V
SSA
V
CCIOPLL
L
L
C
C
Processor
Core
PLL
R
R