AD1881A

–22–

REV. 0

CD-ROM CONNECTIONS

The CD-ROM audio output level should be investigated; typical drives generate 2 V rms output and require a voltage divider for

compatibility with the Codec input (1 V rms range). The recommended circuit is basically a group of divide-by-two voltage dividers

as shown on Figure 10.

The CD_GND_REF pin is used to cancel differential ground noise from the CD-ROM. For optimum noise cancellation, this section

of the divider should have approximately half the impedance of the right and left channel section dividers.

HEADER FOR

CD ROM AUDIO

(LGGR)

1

2

3

4

VOLTAGE

DIVIDER

R1

4.7k

R3

2.7k

4.7k

R5

R2

4.7k

R4

2.7k

R6

4.7k

C1

0.33 F

0.33 F

0.33 F

C2

C3

TO CODEC

CD_L INPUT

TO CODEC

CD_GND_REF

INPUT

TO CODEC

CD_R INPUT

+

+

+

Figure 10. Typical CD-ROM Audio Connections

LINE_IN, AUX AND VIDEO INPUT CONNECTIONS

Most of these audio sources also generate 2 V rms audio level and require a –6 dB input voltage divider to be compatible with the

Codec inputs. Figure 11 shows the recommended application circuit. For applications requiring EMC compliance, the EMC compo-

nents should be configured and selected to provide adequate RF immunity and emissions control.

1

2

3

4

R1

4.7k

R2

4.7k

C3

0.33 F

0.33 F

C4

TO CODEC

RIGHT CHANNEL

INPUT

+

+

5

R3

4.7k

R4

4.7k

TO CODEC

LEFT CHANNEL

INPUT

L2 600Z

L1 600Z

C1

470pF

C2

470pF

EMC

COMPONENTS

VOLTAGE

DIVIDER

AC-COUPLING

LINE/AUX/VIDEO

INPUT

J1

Figure 11. LINE_IN, AUX, and Video Input Connections

MICROPHONE CONNECTIONS

The AD1881A contains an internal microphone preamp with 20 dB gain, in most cases a direct microphone connection as shown in

Figure 12 is adequate. If the microphone level is too low, an external preamp can be added as shown in Figure 13. In either case the

Ω resistor. For the preamp circuit, the

To meet the PC99 1.0A requirements, the MIC signal should be placed on the microphone jack tip and the bias on the ring. This

configuration supports electret microphones with three conductor plugs, as well as dynamic microphones with two conductor plugs

(ring and sleeve shorted together).

Additional filtering may be required to limit the microphone response to the audio band of interest.