CRD4205-2
2.4
PCI Bus
meant as starting points. Modify these values to
meet individual EMC requirements.
The PCI bus is only used to supply power to the
board, so that an external supply is not required.
The PCI bus connections are shown in Figure 4.
The digital power is supplied from the PCI bus. A
Motorola MC78M05C regulates the +12 V supply
from the PCI bus down to a clean +5 V analog sup-
ply. For the best audio performance, the analog
voltage regulator is located over the analog ground
plane near the partition between the analog and dig-
ital planes. The regulator ground pin is connected
to the analog ground.
Figure 4 also shows the docking port header. This
connector couples the serial data from the
CRD4205-1 and is buffered by a 74HC244 octal
buffer.
3. GROUNDING AND LAYOUT
One of the most critical aspects of PC audio design
is good PC board layout. The PC is a hostile envi-
ronment for audio, and good layout is essential for
achieving high audio quality.
The CRD4205-2 is partitioned into a digital and an-
alog sections to help isolate noisy digital circuitry
from quiet analog audio circuitry. The most impor-
tant rule for successful PC audio layout is to keep
all digital signal traces and components over the
digital ground plane, and all analog signal traces
and components over an analog ground plane.
These planes are separated by a minimum of 60 to
100 mils (0.060 to 0.100 inches).
When digital and analog signals cross planes, they
introduce noise into the audio section reducing per-
formance. The CS4334 DACs and CS5331A
ADCs are placed over the partition of the analog
and digital ground planes. The ADCs and DACs
both have their analog and digital signals parti-
tioned to opposite sides of the ICs to help simplify
PCB layout. Digital and analog ground are tied to-
gether by a wide trace (over 50 mils or
0.050 inches) at a single point underneath the con-
verters in order to provide a common ground refer-
ence.
For more information on layout specifically for the
CS4334 and the CS5331A, see their respective
datasheets.
2.5
Component Selection
Great attention was given to the particular compo-
nents used on the CRD4205-2 board with cost, per-
formance, and package selection as the most
important factors. Listed are some of the guidelines
used in the selection of components:
•
•
•
No components smaller than 0805 package.
Only single package components; no resistor
packs.
All ICs are in surface mount packages.
2.6
EMC Components
A number of capacitors and inductors are included
to help the board meet EMI compliance tests, such
as FCC Part 15. The EMC part values are only
4
DS489RD2A1
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