TEA7063DP datasheet(6/15 Pages) STMICROELECTRONICS

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2. TRANSMISSION CHAIN

2.1 A.G.C. In Transmission

The transmission gain between Microphone Input

(pin 7) and Vline (pin 16) is internally decreased

of 6dB when the line current varies from ILL to

ILS with a constant AC load of 600

Ω.

The values of ILL (long line current) and ILS (short

line current) are programmable through I-start (pin

9) and I-slope (pin 15) (see also paragr. 4).

2.2 Sending Impedance

The impedance of the Output Stage Amplifier, Zout,

is determined by the impedance Z4 (at pin 3).

Zout = 10.65 xZ4

The total AC impedance shown to the line is the

parallel

Zpar =Zout//Zint//Zext

where:

-Zint = 10K

Ω//8.5 nF (internal)

-Zext = R6//C4 (at pin 16)

2.3 Sending Mute

In normal speech operation (Vmute at pin 14 <

0.8V), the signal at Microphone Input (pin 7) is

amplified to Vline (pin 16) with the gain Gs (long

line) or 6dB lower (shorter lines) depending on

AGC control (see paragr. 4).

In sending mute condition (V 14 > 1.6V) these

gains are reduced of at least 60dB. In the same

condition, DTMF input (pin 6) is activated, with

gain Gmf to the line independent from Iline lenght.

2.4 Antisidetone Buffer

The signal coming from the sending preamplifier

is internally presented at pin 4 and than buffered

to pins 1 and 2 for sidetone cancellation (see

paragraph 3.2).

Figure 3

TEA7063

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