Ground And Power Planes; Figure B-3. Ground Layer Layout Example - VIA Technologies Apollo Pro133A Design Manual

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B.2.2 Ground and Power Planes:
It is recommended to include partitioned digital and analog power planes directly over their respective ground planes. The power-
ground sandwich with a substrate separation can provide an extremely effective, low ESR & ESL bypass capacitance. The audio
IC leads will have pads and vias that go directly to the appropriate plane for power and ground. All digital components are
mounted over the digital power/ground plane sandwich and all analog components over the analog power/ground sandwich. This
doesn't avoid the need for additional ceramic bypass capacitors at the IC pins as mentioned above. The importance and
effectiveness of ground planes cannot be over emphasized to optimize the performance of the codec.
Ground planes
VIA recommends having separate analog and digital ground planes on the PCB ground layer (2
pins of the codec and all digital support components should be over the digital ground. All analog pins and analog support
components should be over the analog ground plane. Three analog ground planes (GND_AUD, GND_LOUT and GND_MIDI)
and one digital ground plane (GND) are shown in Figure B-3.
planes. The line out circuit should refer to its own analog ground partition (GND_LOUT) instead of GND_AUD for better signal
consideration.
All digital routing should not run over the analog plane. If it is necessary to route a digital signal over the analog plane the trace
length should be short and the digital signal should be static. All analog routing should be over the analog plane. When analog
signals need to cross the gap in the ground plane (when connecting the jacks for example) components such as ferrite beads or 0
ohm shorts should be used. Signal traces should never cross the gap between the ground planes.
The analog ground and digital ground planes should be connected through only one ferrite bead (preferred) or a series 0 ohm
resistor. The recommended location for the ferrite bead or the 0-ohm resistor is on the quietest area where have no signals passing
around.
Preliminary Revision 0.5, November 19, 1999
Guidelines
Design Guide - VT82C694X Apollo Pro133 with VT82C686A
Table B-4 lists the audio signals covered by different ground

Figure B-3. Ground Layer Layout Example

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Appendix B - Audio Codec and Game/MIDI Port Layout
layer in our case). All digital