tea1065t NXP Semiconductors, tea1065t Datasheet - Page 11

• Manufacturer Part Number: tea1065t
• Description: Versatile Telephone Transmission Circuit With Dialler Interface
• Manufacturer: NXP Semiconductors

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Philips Semiconductors
Automatic gain control
Automatic compensation of line loss is obtained by connecting a resistor (R6) between AGC and V
control varies the gain of the microphone amplifier and receiving amplifier in accordance with the DC line current (see
Fig.12). The control range is 5.9 dB; this corresponds to a line length of 3.5 km of twisted pair cable (see Fig.11). The
DTMF gain is not affected by this feature.
If automatic line loss compensation is not required the AGC pin can be left open-circuit, the amplifiers then give their
maximum gain.
March 1994
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Versatile telephone transmission circuit with
dialler interface
Fig.12 Variation of gain as a function of line current with R6 as a parameter; R9 = 20 .
Fig.11 Typical 0.5 km line cell model used for automatic gain control optimization.
(dB)
G v
1
0
1
3
5
7
0
34.8
34.8
20
75 H
75 H
13 nF
R6 =
86.6 k
40
11
118 k
24.3 nF
24.3 nF
75 H
75 H
60
R6 =
147 k
I line (mA)
34.8
34.8
MBA572
187 k
MBA549
80
EE
Product specification
. The automatic gain
TEA1065