AD1885

–26–

REV. 0

PC_BEEP INPUT CONNECTIONS

The recommended PC_BEEP input circuit is shown below. Under most cases the PC_BEEP signal should be attenuated, filtered and

then ac-coupled into the Codec.

TO CODEC PC_BEEP INPUT

PC_BEEP (FROM ICH)

Figure 17. Recommended PC_BEEP Connections

GROUNDING AND LAYOUT

To reduce noise and emissions, Analog Devices recommends a split ground plane as shown in Figure 18. The purpose of splitting

the ground plane is to create a low noise analog area that is somewhat isolated from the digital ground current noise generated

by the system’s logic. All the analog circuitry should be placed on the analog ground plane area.

For reference purposes, and to return power supply currents, the analog and digital ground planes must be connected at some point,

ideally a small bridge under or near the Codec should be provided. A 0

Ω resistor or a ferrite bead should also be considered since

these allow some flexibility in optimizing the layout to meet EMC requirements.

PIN 1

ISOLATION

TRENCH

CONNECT SPLIT GROUND

PLANES AT OR NEAR CODEC.

ANALOG

GROUND PLANE

DIGITAL

GROUND PLANE

AD1885

Figure 18. Recommended Split Ground Plane

ANALOG POWER SUPPLY

To minimize audio noise, the Codec analog power supply (AVDD) should be well decoupled and regulated. In PC systems it is rec-

ommended that the analog supply be derived from the 12 V PC power supply using a localized linear voltage regulator. Preferably,

the analog power supply should be connected to the Codec’s analog section using a ferrite bead.

If a power plane layer is being used in the system design, it is recommended that the analog power plane for the Codec also be split

(mirroring the analog ground plane). In this case, the analog power supply ferrite bead should bridge the isolation trench, close to

the Codec location.