TEA1098ATV PHILIPS [NXP Semiconductors], TEA1098ATV Datasheet - Page 14

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

Philips Semiconductors
Loudspeaker amplifier (pins HFRX, GALS and LSAO)
The TEA1098A has an asymmetrical input for the
loudspeaker amplifier with an input resistance of 20 k
between pins HFRX and GND. It is biased at two diodes
voltage. Without limitation from the output, the input stage
can accommodate signals up to 580 mV (RMS) at room
temperature for 2% of THD.
The gain of the input stage varies according to the mode
of the TEA1098A. In the receive mode, the gain is at its
maximum; in the transmit mode, it is at its minimum and in
the Idle mode, it is halfway between maximum and
minimum. Switch-over from one mode to the other is
smooth and click-free. The rail-to-rail output stage is
designed to power a loudspeaker connected as a
single-ended load (between pins LSAO and GND).
In the receive mode, the overall gain of the loudspeaker
amplifier can be adjusted from 0 dB up to 35 dB to suit
specific application requirements. The gain from HFRX to
LSAO is proportional to the value of R
28 dB with R
parallel with R
first-order low-pass filter.
Digital volume control (pins LVCI and EVCI)
The loudspeaker amplifier gain can be adjusted
(attenuated) with the LVCI logic input (as MSB) and the
4-level input EVCI (as LSBs). This combination provides
8 steps of 4 dB which applies in all handsfree receive
modes.
Dynamic limiter (pin DLC)
The dynamic limiter of the TEA1098A prevents clipping of
the loudspeaker output stage and protects the operation of
the circuit when the supply voltage at V
Hard clipping of the loudspeaker output stage is prevented
by rapidly reducing the gain when the output stage starts
to saturate. The time in which gain reduction is effected
(clipping attack time) is approximately a few milliseconds.
The circuit stays in the reduced gain mode until the peaks
of the loudspeaker signals no longer cause saturation. The
gain of the loudspeaker amplifier then returns to its normal
value within the clipping release time (typically 250 ms).
Both attack and release times are proportional to the value
of the capacitor C
loudspeaker output stage, in reduced gain mode, stays
below 2% up to 10 dB (minimum) of input voltage
overdrive [providing V
2000 Mar 21
Speech and handsfree IC
GALS
GALS
DLC
= 255 k . A capacitor connected in
is recommended and provides a
. The total harmonic distortion of the
HFRX
is below 580 mV (RMS)].
GALS
BB
falls below 2.7 V.
and equals
14
When the supply voltage drops below an internal threshold
voltage of 2.7 V, the gain of the loudspeaker amplifier is
rapidly reduced (approximately 1 ms). When the supply
voltage exceeds 2.7 V, the gain of the loudspeaker
amplifier is increased again.
By forcing a level lower than 0.2 V on pin DLC, the
loudspeaker amplifier is muted and the TEA1098A is
automatically forced into the transmit mode.
D
Signal and noise envelope detectors (pins TSEN, TENV,
TNOI, RSEN, RENV and RNOI)
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 illustrated in
Fig.10.
For the transmit channel, the input signal at pin TXI is
40 dB amplified to TSEN. For the receive channel, the
input signal at pin HFRX 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
and R
two resistors block any DC component and form a
first-order high-pass filter. In the basic application
(see Fig.18) it is assumed that V
V
R
C
The buffer amplifiers feeding the compressed signals to
pins TENV and RENV have a maximum source current of
120 A and a maximum sink current of 1 A. Capacitors
C
monitors. 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.
HFRX
UPLEX CONTROLLER
RSEN
RSEN
TENV
RSEN
= 100 mV (RMS) nominal and both R
have a value of 10 k . With the value of C
and C
at 100 nF, the cut-off frequency is at 160 Hz.
. The capacitors connected in series with the
RENV
set the timing of the signal envelope
TXI
Preliminary specification
= 1 mV (RMS) and
TEA1098A
TSEN
TSEN
and
TSEN
and