Layout and Routing Guidelines
4-32
Intel
®
810A3 Chipset Design Guide
4.15
RAMDAC/Display Interface
Figure 4-34
shows the interface of the RAMDAC analog current outputs with the display. Each
DAC output is doubly-terminated with a 75
Ω
resistance; one 75
Ω
resistance from the DAC
output to the board ground and the other termination resistance exists within the display. The
equivalent dc resistance at the output of each DAC output is 37.5
Ω
. The output current of each
DAC flows into this equivalent resistive load to produce a video voltage without the need for
external buffering. There is also an LC pi-filter which is used to reduce high-frequency glitches and
noise, and reduce EMI. To maximize the performance, the filter impedance, cable impedance and
load impedance should be the same. The LC pi-filter consists of two 3.3 pF capacitors and a ferrite
bead with a 75
Ω
impedance at 100 MHz. The LC pi-filter is designed to filter glitches produced by
the RAMDAC while maintaining adequate edge rates to support high-end display resolutions.
NOTE: Diodes D
1
, D
2
are clamping diodes and may not be necessary to populate.
Figure 4-34. Schematic of RAMDAC Video Interface
R A M D A C
V C C D A C A 1 /
V C C D A C A 2
V C C D A
R E D
Graphics
Chip
Pixel
C l o c k
( F r o m
D P L L )
C f
L f
L C
Filter
1 . 8 V B o a r d
P o w e r P l a n e
D i s p l a y P L L P o w e r
Connects to this
S e g m e n t e d P o w e r
P l a n e
1 . 8 V B o a r d
P o w e r P l a n e
1 . 8 V B o a r d
P o w e r P l a n e
R t
D 2
D 1
C 1
C 2
F B
pi Filter
1 . 8 V B o a r d
P o w e r P l a n e
R t
D 2
D 1
C 1
C 2
F B
pi Filter
1 . 8 V B o a r d
P o w e r P l a n e
R t
D 2
D 1
C 1
C 2
F B
pi Filter
G R E E N
B l u e
V S S D A C A
A n a l o g
P o w e r P l a n e
1 . 8 V
I R E F
I W A S T E
G r o u n d P l a n e
R s e t 1 % R e f e r e n c e
Current Resistor
(metal film)
V i d e o
C o n n e c t o r
Graphics Board
R e d
G r e e n
B l u e
C o a x
C a b l e
Z o = 7 5
Ω
7 5
Ω
7 5
Ω
7 5
Ω
Display
Termination Resistor, R 75
Ω
1 %
(metal film)
D i o d e s D 1 , D 2 : S c h o t t k y D i o d e s
LC Filter Capacitors, C1, C2: 3.3 pF
Ferrite Bead, FB: 7
Ω
@ 1 0 0 M H z
( R e c o m m e n d e d p a r t : m u R a t a
B L M 1 1 B 7 5 0 S )
Содержание 810A3
Страница 1: ...Intel 810A3 Chipset Platform Design Guide July 2000 Order Number 298186 002...
Страница 11: ...1 Introduction...
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Страница 25: ...2 PGA370 Processor Design Guidelines...
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Страница 41: ...3 SC242 Processor Design Guidelines...
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Страница 115: ...6 Clocking...
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Страница 123: ...7 System Design Considerations...
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Страница 157: ...9 Third Party...
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Страница 163: ...A PCI Devices Functions Registers Interrupts...
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