TEA7540 ST Microelectronics, Inc., TEA7540 Datasheet - Page 4

• Manufacturer Part Number: TEA7540
• Description: Handsfree Controller
• Manufacturer: ST Microelectronics, Inc.

TEA7540
stracted from the incoming signal before the com-
parison. So very high noise level in one mode
cannot trouble the comparison between the useful
signals.
The result of the comparison manages the attenu-
ators in the following way:
Figure A
Figure B
4/13
- The maximum attenuation is switched on
SPEECH/NOISE
the mode where the speech signal is the
lowest. The maximum attenuation is fixed
by two external resistor (maximum 52dB).
Em Rec
A max dB
0dB
1
1
0
0
- When neither party is talking both attenu-
The time constant of the switch is fixed by
the timer via an external capacitor.
ators are set to a medium attenuation.
Thus each mode is in idle mode. The time
constant of the switch from active mode to
idle mode must be long enough to prevent
from switching to idle mode between two
words (see fig.B). This time constant is
fixed by an external RC.
D93TL009A
IDLE (A max/2)