TWL1102

VOICE-BAND AUDIO PROCESSOR (VBAP

™)

SLVS264 – NOVEMBER 1999

21

POST OFFICE BOX 655303

PRINCIPLES OF OPERATION

transmit operation (continued)

_

+

_

+

Vref

510 k

Ω

510 k

Ω

34 k

Ω

34 k

Ω

Ci MIC1N

Ci MIC1P

M

I

C

Rmic

Rmic

MBIAS

Figure 7. Typical Microphone Interface

microphone mute function

Transmit channel muting provides 80-dB attenuation of input microphone signal. The MICMUTE function can

transmit channel gain control

The values in the transmit PGA control registers control 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

BIT NAME

MIC AMP1

MIC AMP2

TX PGA

GAIN

MODE

TOTAL TX GAIN

TP3

TP2

TP1

TP0

GAIN

GAIN

GAIN

MIN

TYP

MAX

UNIT

0

0

0

0

23.5

12

0

Extended

35.3

35.5

35.7

dB

0

0

0

1

23.5

12

–2

Extended

33.3

33.5

33.7

dB

0

0

1

0

23.5

12

–4

Extended

31.3

31.5

31.7

dB

0

0

1

1

23.5

12

–6

Extended

29.3

29.5

29.7

dB

0

1

0

0

23.5

12

–8

Extended

27.3

27.5

27.7

dB

0

1

0

1

23.5

12

–10

Extended

25.3

25.5

25.7

dB

1

0

0

0

23.5

0

0

Normal

23.3

23.5

23.7

dB

1

0

0

1

23.5

0

–2

Normal

21.3

21.5

21.7

dB

1

0

1

0

23.5

0

–4

Normal

19.3

19.5

19.7

dB

1

0

1

1

23.5

0

–6

Normal

17.3

17.5

17.7

dB

1

1

0

0

23.5

0

–8

Normal

15.3

17.5

17.7

dB

1

1

0

1

23.5

0

–10

Normal

13.3

13.5

13.7

dB