w681513 Winbond Electronics Corp America, w681513 Datasheet - Page 30

• Manufacturer Part Number: w681513
• Description: 5v Single-channel Voiceband Codec For Usb Applications
• Manufacturer: Winbond Electronics Corp America

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
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
1.5K
1.5K
SUGGESTED COMPONENT VALUES BY APPLICATION
RMS
COMPONENT #
SCHEMATIC
Figure 11.2 Equivalent Circuit of Figure 11.1
. The chamber typically has a gain of 3 over a bare microphone (or
MICROPHONE
1.0uF
1.0uF
SPEAKER
R3,4
R5,6
C6,7
R9
R7
R8
R3
R4
3.9K
3.9K
PAO-
PAO+
TELEPHONE
HANDSET
R8
SELECT
1200 pF
- 30 -
27K
20K
1K
3K
22uF
3K
PAI
AI-
AI+
R6
C7
C6
R5
AO
62K
330pF
1K
330pF
62K
R7
VoIP PHONE
R9
SELECT
20K
330 pF
SET
91K
20K
select
1K
3K
VAG
0.01uF
VCC
RO+
W681513