TEA7092 datasheet(21/57 Pages) STMICROELECTRONICS

21 / 57 page

II - SPEECH FEATURES (continued)

II.3 - Transmit Channel (continued)

Figure 28 g ives the t ransmit line level at

Pin VL (Pin 3) and the transmit distortion versus the

input microphone level (Pin MIC1 (Pin 23) &

Pin MIC2 (Pin 24)) for R12 = 82k

Ω, R1 = 47kΩ &

R8 = 1.62k

Ω.

L (mA)

2040

6080

100

-6

-4

-2

R18 = 18k

Ω

R18 = 10k

Ω

R18 = 8.2k

Ω

R18 = 6.8k

Ω

R18 = 5.6k

Ω

Figure 31 : dGtx = f(IL)

0.2

0.5

50 100

MIC (mVRMS)

0.05

0.1

0.2

0.5

LINE

Distortion

Figure 28 : Tx Output Level & Distortion (IL=20mA)

Figure 29 gives the maximum transmit level at

Pin VL (Pin 3) versus R1, for R3 = 2.7k

Ω & for

different values of R12, at IL = 40mA.

II.3.3 - Line Loss Compensation/

A.G.C. Adjustment

The TEA7092 uses a line current information to

control the transmit and receive gains variation

versus the line current.

TheAutomaticGainControl (A.G.C.)versus linelength

works in the same way for transmit and receive paths.

Through two external resistors the line current vari-

ation, where the A.G.C. occurs, is programmable :

- R18 connected on Pin ILL (Pin 33) sets up the

start up line current value, ILL, for the A.G.C.

R18

300

ILL

− 5.6

in k

Ω ;ILL in mA

- R19 connected on Pin ISL (Pin 34) sets up the

slope and the line current value, ISL, where the

transmit and receive gains are equal to the maxi-

mum gain value minus 6dB.

R19

300

ISL

− 5.6

in k

Ω ;ISL in mA

For line current values lower than ILL, the transmit

and receive gains stay at their maximum values.

For line current values upper than ISL, the transmit

and receive gains stay at their minimum values.

Figure 30 gives A.G.C. with a constant start value

(IL = 20mA) and different values of R19.

Figure 31 gives A.G.C. with a constant stop value

(IL = 100mA) and different values of R18.

R1 (k

Ω)

0.25

0.5

0.75

1.25

1.5

20406080

100

120

1.75

2.25

2.5

2.75

3.25

R12 = 68k

Ω

R12 = 82k

Ω

R12 = 110k

Ω

Figure 29 : Vac Max On Line

II.3.4 - A.G.C. Inhibition

The A.G.C. feature can be inhibited through the

serial bus interface by sending the code 0010100.

This code is a toggle one.

When the no A.G.C. mode is selected the transmit

and receive gains stay at their maximum values

-2dB over the line current range variation.

This feature is used for a telephone set connected

behind a PABX or in a country where the A.G.C.

feature is not requested.

L (mA)

2040

6080

100

-6

-4

-2

R19 = 8.2k

Ω

R19 = 6.8k

Ω

R19 = 4.7k

Ω

R19 = 3.9k

Ω

R19 = 3.3k

Ω

Figure 30 : dGtx = f(IL)

TEA7092 - TELEPHONE SET INTEGRATED CIRCUIT

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