W681513_05 Datasheet, PDF (30/35 Pages) Winbond – 5V SINGLE-CHANNEL VOICEBAND CODEC FOR USB APPLICATIONS

W681513
1.5K
R3 3.9K
1.0uF
MICROPHONE
1.5K
1.0uF R4 3.9K
22uF
1K
C6 330pF
VCC
R5 62K
AI-
AO
AI+
R6 62K
C7 330pF
VAG
0.01uF
R8 3K
SPEAKER
PAO-
PAI
PAO+
R9 select
R7 20K
RO+
Figure 11.2 Equivalent Circuit of Figure 11.1
SUGGESTED COMPONENT VALUES BY APPLICATION
SCHEMATIC
COMPONENT #
R3,4
R5,6
C6,7
R9
R7
R8
TELEPHONE
HANDSET
1K
27K
1200 pF
SELECT
20K
3K
VoIP PHONE
SET
1K
91K
330 pF
SELECT
20K
3K
In the handset application the gain from the handset microphone is set to 27 for the input amplifier.
This is because the acoustical chamber in the telephone type handset lets the electret microphone
provide an output of ~28 mV_RMS. The chamber typically has a gain of 3 over a bare microphone (or
one placed with only a small opening to the outside world.) Because of the high sensitivity of the
earphone (150 Ώ impedance) in a typical handset, the output gain from the Power Amp is set to ~0.16
for a satisfactory listening level.
In the VoIP telephone, or small wireless phones, the plastic case is typically too small to provide a
reasonable acoustic chamber. Thus the output from the microphone is less than in the previous
example. This results in having to set the input gain of the CODEC to ~75 to 90 and in a comparable
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