ꢀ ꢁꢂ ꢃ ꢄꢅ ꢆꢇ ꢈ ꢉꢉ ꢅꢃ
SLAS356 − DECEMBER 2001
PRINCIPLES OF OPERATION
transmit operation (continued)
_
MBIAS
+
V
ref
R
R
mic
510 kΩ
C MIC1N
i
34 kΩ
34 kΩ
_
+
M
I
C
C MIC1P
i
510 kΩ
mic
Figure 7. Typical Microphone Interface
microphone mute function
Transmit channel muting provides 80-dB attenuation of input microphone signal. The MICMUTE function can
2
be selected by setting bit 6 of the power control register through the I C interface.
transmit channel gain control
The values in the transmit PGA control registers control the gain in the transmit path. The total TX channel gain
can vary from 35.5 dB to 13.5 dB. The default total TX channel gain is 23.5 dB
Table 4. Transmit Gain Control
GAIN
MODE
BIT NAME
TP2 TP1
MIC AMP1 MIC AMP2
TX PGA
TOTAL TX GAIN
TP3
0
TP0
0
GAIN
23.5
23.5
23.5
23.5
23.5
23.5
23.5
23.5
23.5
23.5
23.5
23.5
GAIN
12
12
12
12
12
12
0
GAIN
0
MIN
35.3
33.3
31.3
29.3
27.3
25.3
23.3
21.3
19.3
17.3
15.3
13.3
TYP
35.5
33.5
31.5
29.5
27.5
25.5
23.5
21.5
19.5
17.5
17.5
13.5
MAX
35.7
33.7
31.7
29.7
27.7
25.7
23.7
21.7
19.7
17.7
17.7
13.7
UNIT
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
0
0
0
0
1
1
0
0
0
0
1
1
0
0
1
1
0
0
0
0
1
1
0
0
Extended
Extended
Extended
Extended
Extended
Extended
Normal
0
1
−2
−4
−6
−8
−10
0
0
0
0
1
0
0
0
1
1
0
1
1
0
−2
−4
−6
−8
−10
Normal
1
0
0
Normal
1
1
0
Normal
1
0
0
Normal
1
1
0
Normal
22
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