TEA1098ATV PHILIPS [NXP Semiconductors], TEA1098ATV Datasheet - Page 16

• Manufacturer Part Number: TEA1098ATV
• Description: Speech and handsfree IC
• Manufacturer: PHILIPS [NXP Semiconductors]

Philips Semiconductors
Decision logic (pins IDT and SWT)
The TEA1098A selects its mode of operation (transmit,
receive or Idle mode) by comparing the signal and the
noise envelopes of both channels. This is executed by the
decision logic. The resulting voltage on pin SWT is the
input for the voice-switch.
To facilitate the distinction between signal and noise, the
signal is considered as speech when its envelope is more
than 4.3 dB above the noise envelope. At room
temperature, this is equal to a voltage difference
V
threshold is implemented in both channels.
The signal on pin TXI contains both speech and the signal
from the loudspeaker (acoustic coupling). When receiving,
the contribution from the loudspeaker overrules the
speech.
2000 Mar 21
handbook, full pagewidth
ENV
Speech and handsfree IC
(1) When DLC < 0.2 V, 10 A is forced.
V
NOI
RENV
= 13 mV. This so-called speech/noise
TENV
RNOI
TNOI
8 (3)
7 (2)
12 (7)
10 (5)
from logic
ATTENUATOR
from dynamic
limiter
13 mV
13 mV
V dt
DUPLEX CONTROLLER
Fig.12 Decision logic.
X
X
X
1
0
16
X
X
X
1
0
As a result, the signal envelope on pin TENV is formed
mainly by the loudspeaker signal. To correct this, an
attenuator is connected between pin TENV and the
TENV/RENV comparator. Its attenuation equals that
applied to the microphone amplifier.
When a dial tone is present on the line, without monitoring,
the tone would be recognized as noise because it is a
signal with a constant amplitude. This would cause the
TEA1098A to go into the Idle mode and the user of the set
would hear the dial tone fade away. To prevent this, a dial
tone detector is incorporated which, in standard
applications, does not consider input signals between
HFRX and GND as noise when they have a level greater
than 25 mV (RMS). This level is proportional to R
LOGIC
1
0
0
1
0
(1)
1
X
X
0
X
10 A
10 A
10 A
0
0
V ref
(25) 28
(24) 27
FCA153
IDT
SWT
Preliminary specification
TEA1098A
R IDT
C SWT
RSEN
.