tea1094t NXP Semiconductors, tea1094t Datasheet - Page 9

• Manufacturer Part Number: tea1094t
• Description: Hands Free Ic
• Manufacturer: NXP Semiconductors

Philips Semiconductors
L
The TEA1094 and TEA1094A have symmetrical inputs for
the loudspeaker amplifier with an input resistance of 40 k
between RIN1 and RIN2 (2
accommodate signals up to 390 mV (RMS) at room
temperature for 2% of total harmonic distortion (THD).
The gain of the input stage varies according to the mode
of the TEA1094 and TEA1094A. 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 LSP and GND).
In the receive mode, the overall gain of the loudspeaker
amplifier can be adjusted from 0 dB up to 33 dB to suit
specific application requirements. The gain from
RIN1 and RIN2 to LSP is proportional to the value of R
and equals 18.5 dB with R
connected in parallel with R
first-order low-pass filter.
V
The loudspeaker amplifier gain can be adjusted with the
potentiometer R
obtain logarithmic control of the gain at the loudspeaker
amplifier. Each 950
loss of 3 dB. The maximum gain reduction with the volume
control is internally limited to the switching range.
D
The dynamic limiter of the TEA1094 and TEA1094A
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
distortion of the loudspeaker output stage, in reduced gain
mode, stays below 5% up to 10 dB (minimum) of input
voltage overdrive [providing V
1996 Jul 15
OUDSPEAKER AMPLIFIER
OLUME CONTROL
YNAMIC LIMITER
Hands free IC
BB
falls below 2.9 V.
VOL
:
:
PIN
PIN
. A linear potentiometer can be used to
DLC/MUTER
VOL
increase of R
:
PINS
GAR
DLC
GAR
20 k ). The input stage can
RIN
RIN1, RIN2, GAR
= 66.5 k . A capacitor
. The total harmonic
can be used to provide a
is below 390 mV (RMS)].
VOL
results in a gain
AND
LSP
GAR
9
When the supply voltage drops below an internal threshold
voltage of 2.9 V, the gain of the loudspeaker amplifier is
rapidly reduced (approximately 1 ms). When the supply
voltage exceeds 2.9 V, the gain of the loudspeaker
amplifier is increased again.
By forcing a level lower than 0.2 V on pin DLC/MUTER, the
loudspeaker amplifier is muted and the TEA1094
(TEA1094A) 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.7.
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.13, 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.
IGNAL AND NOISE ENVELOPE DETECTORS
RIN
= 100 mV (RMS) nominal and both R
TSEN
and R
TENV
and C
RSEN
TEA1094; TEA1094A
. The capacitors connected in
RENV
AND
, the timing of the signal
MIC
RNOI
= 1 mV (RMS) and
Product specification
:
PINS
TSEN
TSEN
TSEN,
and C
and R
RSEN
RSEN