Table B-3. Ac-Coupling Capacitors For Audio Input Signals - VIA Technologies Apollo Pro133A Design Manual

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Notes

1. Use all ac-coupling capacitors in 1206 package.

2. Use the same ac-coupling mechanism when the function is applied.

These audio input ac-coupling capacitors in Table B-2 should be placed near the audio codec. For example, C13, C12, and C14

should be placed near pins CD_L, CD_R and CD_GND of the audio codec respectively since they take their CD-in signal from the

CD_IN header.

The line-out signals are delivered from the audio codec to the LINE_OUT jack through the audio amplifier. Therefore, these audio

output ac-coupling capacitors in Table B-3 should be placed near the audio amplifier. C17 and C18 should be placed near pins

INB and INA of the audio amplifier respectively since they receive the line-out signal from the audio codec. This audio amplifier

should be placed close to the LINE_OUT jack from preventing any noise coupling.

Referring to Figure B-2, C15, C16 and C23 are close to the audio codec since they take their signal from the LINE_IN and

MIC_IN jacks. The ac-coupling capacitors C13, C12 and C14 are close to the audio codec since they take their signal from the on-

board CD_IN header. The ac-coupling capacitor C24 is close to the audio codec since it receives the speaker signal from the

VT82C686A south bridge controller.

Voltage Regulators

The DC-DC voltage regulator supplies the 5V analog power to the audio codec from +12V system power. In this manner, noise

form other digital powers can be isolated by the regular and a quiet analog power can be obtained through a ferrite bead. The

+12V input and 5V output (VDD5) routings should be made over the digital ground plane. The 5V output is set close the analog

section of the codec through a ferrite bead. The analog 5V routing (AVDD5) should be over the analog ground plane. See Section

B.2.2 for more information on digital and analog ground planes.

Referring to Figure B-2, the regulator locating on the upper-left side of the audio codec can provide the shortest power path to the

audio codec.

On-board Audio Connectors

CD_IN headers and other on-board audio connectors such as telephony audio can be placed anywhere over the analog ground

plane. That is, they do not need to be close to the codec, but do need to be enclosed by a ground plane. The analog ground plane

is chosen since it is the quietest ground.

Referring to Figure B-2, the CD_IN header was placed close to the codec and the ac-coupling capacitors C12, C13 and C14 as well

as resistors R12, R13, R14, and R15 were laid between the codec and header to keep the layout tight to reduce noise coupling and

DC offsets.

Preliminary Revision 0.5, November 19, 1999

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