AD1885

–25–

REV. 0

MICROPHONE CONNECTIONS

The AD1885 contains an internal microphone preamp with 20 dB gain; in most cases a direct microphone connection as shown in

Figure 14 is adequate. If the microphone level is too low, an external preamp can be added as shown in Figure 15. In either case the

Ω resistor. For the preamp circuit,

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.

AC-COUPLING

TO CODEC MIC1 OR MIC2 INPUT

FROM CODEC VREFOUT

MIC INPUT

1

2

3

4

5

J1

EMC

COMPONENTS

C1

470pF

C2

470pF

L2 600Z

L1 600Z

MIC BIAS

Figure 14. Recommended Microphone Input Connections

4

TO CODEC MIC1 OR MIC2 INPUT

FROM CODEC VREFOUT

AC-COUPLING

MIC INPUT

1

2

3

4

5

J1

EMC

COMPONENTS

C1

470pF

C2

470pF

L2 600Z

L1 600Z

MIC BIAS

AVDD

U1

PREAMP

AD8531

Figure 15. Microphone with Additional External Preamp (20 dB Gain)

LINE OUTPUT CONNECTIONS

The AD1885 Codec provides stereo LINE_OUT signals at a standard 1 V rms level. These signals must be ac-coupled before they

can be connected to an external load. After the ac-coupling, a minimal resistive load is recommend to keep the capacitors properly

biased and reduce click and pop when plugging stereo equipment into the output jack. The capacitor values should be selected to

provide a desired frequency response, taking into account the nominal impedance of the external load. To meet the PC99 specifica-

tion for PCs, testing must be performed with a 10 k

Ω load, therefore a 1 µF value is recommended to achieve less than –3 dB

roll-off at 20 Hz.

FROM CODEC LINE_OUT_R

FROM CODEC LINE_OUT_L

AC-COUPLING

J1

EMC

COMPONENTS

C2

470pF

C1

470pF

L1 600Z

L2 600Z

STEREO LINE_OUT JACK

NOTE:

IF AN OUTPUT AMP IS USED,THE

AC-COUPLING CAP VALUES WILL

DEPENDEND ON THE AMP DESIGN.

Figure 16. Recommended LINE_OUT Connections