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B.2 Layout Recommendations
In this section, the layout recommendations on component placement, ground and power plane partitions and routing guidelines
are described in detail. The PCB layer sequence used here is Signal (Component)-Ground-Power-Signal (Solder).
B.2.1 Component Placement
AC'97 Audio Codec and Audio Amplifier
AC'97 audio codec (VT1611A) and audio amplifier (TPA122) are two major components in the audio codec circuitry. An
example placement for AC'97 audio codec and audio amplifier on either ATX or micro-ATX form factor is shown in Figure B-2.
To limit the audio analog grounding area (GND_AUD), it is not recommended to place the audio codec far from the LINE_OUT,
LINE_IN and MIC_IN audio jacks. And the audio amplifier should be located right beside the LINE_OUT audio jack because the
audio line out signals are very sensitive to noise from any other signals.
Figure B-2. AC'97 Audio Codec and GAME/MIDI Port Placement Example
VDD/VSS Capacitive Decoupling
There are analog power signals (two pairs of AVDD/AVSS signals) and digital power signals (two pairs of DVDD/DVSS signals)
on VT1611A audio codec. Local regulation converting from +12V power for analog power supply to VT1611A is strongly
recommended. No local regulation is required for DVDD power supply to VT1611A. Directly using on-board +5V power can
already provide adequate digital power supply to VT1611A through a ferrite bead.
All high frequency AVDD5 decoupling capacitors (less than 10uF, ceramic) should be placed very close to the AVDD/AVSS pins
of VT1611A and the connection from codec pin to capacitor pad should be routed on the same layer with a short and wide trace (or
a small power plane). That is, there should be no vias connecting the decoupling capacitor to the device pin. All high frequency
DVDD5 decoulping capacitors should have short wide traces connecting to DVDD/DVSS to decrease ground bounce and other
noise coupling caused from digital switching. These high frequency DVDD5 decoupling capacitors should be placed very close to
the DVDD/DVSS pins of VT1611A. All high frequency AVDD decoupling capacitors should use the same way described above.
Preliminary Revision 0.5, November 19, 1999
Guidelines
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
100
Appendix B - Audio Codec and Game/MIDI Port Layout
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