Mobile Intel Pentium 4 Processor - M and Intel 845MP/MZ Chipset Platform Design Guide

Mobile Intel

Pentium

4 Processor-M and Intel

845MP/845MZ Chipset Platform

42 Design Guide

general desired filter topology is shown in Figure 14. Not shown in the core is parasitic routing and

excluded from the external circuitry are parasitics associated with each component.

Figure 14. Typical VCCIOPLL, VCCA, and VSSA Power Distribution

VCC_VID

VCCA

VSSA

VCCIOPLL

Processor

Core

PLLs

Motherboard

pkg

1 µF

33 µF

4.7 µH

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 this document will address

the recommendation for the V

CCA

filter design. The same characteristics and design approach is

applicable for the V

CCIOPLL

filter design.

Note: The 1-µF package capacitor in Figure 14 does not exist on the Mobile Intel Pentium 4 Processor-M in

the 478-pin package. It is present for the Mobile Intel Pentium 4 Processor-M only.

The AC low-pass recommendation, with input at VCC_VID and output measured across the capacitor

or C

in Figure 14), 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 recommendation (AC) is graphically shown in Figure 15.