TEA1093T Philips Semiconductors, TEA1093T Datasheet - Page 10

• Manufacturer Part Number: TEA1093T
• Description: Hands-free IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
When the supply conditions drop below the required level,
the gain of the loudspeaker amplifier is reduced in order to
prevent the TEA1093 from malfunctioning. Only the gain of
the loudspeaker amplifier is affected since it is considered
to be the major power consuming part of the TEA1093.
When the TEA1093 experiences a loss of current, the
supply voltage V
loudspeaker amplifiers is slowly reduced (approximately a
few seconds). When the supply voltage continues to
decrease and drops below an internal voltage threshold of
2.75 V, the gain of the loudspeaker amplifier is rapidly
reduced (approximately 1 ms). When normal supply
conditions are resumed, the gain of the loudspeaker
amplifier is increased again. This system ensures that in
the event of large continuous signals, all current is used to
power the loudspeaker while the voltage on pin V
remains at its nominal value.
By forcing a level lower than 0.2 V on pin DLC/MUTER, the
loudspeaker amplifier is muted and the TEA1093 is
automatically forced into the transmit mode.
Duplex controller
S
TENV, TNOI, RSEN, RENV
The signal envelopes are used to monitor the signal level
strength in both channels. The noise envelopes are used to
monitor background noise in both channels. The signal and
noise envelopes provide inputs for the decision logic. The
signal and noise envelope detectors are shown in Fig.8.
1996 Feb 09
handbook, full pagewidth
IGNAL AND NOISE ENVELOPE DETECTORS
Hands-free IC
from
microphone
amplifier
DUPLEX CONTROLLER
BB
decreases. In this event, the gain of the
TSEN
(24)
LOG
28
AND
R TSEN
C TSEN
RNOI
Fig.8 Signal and noise envelope detectors.
TENV
:
(23)
27
PINS
C TENV
TSEN,
to logic
BB
TNOI
(22)
26
C TNOI
10
from
loudspeaker
amplifier
For the transmit channel, the input signal at MIC is 40 dB,
amplified to TSEN. For the receive channel, the differential
signal between RIN1 and RIN2 is 0 dB amplified to RSEN.
The signals from TSEN and RSEN are logarithmically
compressed and buffered to TENV and RENV
respectively. The sensitivity of the envelope detectors is
set with R
series with the two resistors block any DC component and
form a first-order high-pass filter. In the basic application,
see Fig.16, it is assumed that V
V
have a value of 10 k . With the value of C
at 100 nF, the cut-off frequency is at 160 Hz.
The buffer amplifiers leading the compressed signals to
TENV and RENV have a maximum source current of
120 A and a maximum sink current of 1 A. Together with
the capacitor C
envelope monitors can be set. In the basic application, the
value of both capacitors is 470 nF. Because of the
logarithmic compression, each 6 dB signal increase
means 18 mV increase of the voltage on the envelopes
TENV or RENV at room temperature. Thus, timings can be
expressed in dB/ms. At room temperature, the 120 A
sourced current corresponds to a maximum rise-slope of
the signal envelope of 85 dB/ms. This is sufficient to track
normal speech signals. The 1 A current sunk by TENV
or RENV corresponds to a maximum fall-slope of
0.7 dB/ms. This is sufficient for a smooth envelope and
also eliminates the effect of echoes on switching
behaviour.
RIN
= 100 mV (RMS) nominal and both R
TSEN
RSEN
(21)
LOG
25
and R
TENV
R RSEN
C RSEN
and C
RSEN
RENV
. The capacitors connected in
RENV
(20)
24
, the timing of the signal
C RENV
MIC
to logic
= 1 mV (RMS) and
RNOI
Product specification
(19)
23
TEA1093
TSEN
TSEN
MGD223
C RNOI
and R
and C
RSEN
RSEN