TEA1098 Philips Semiconductors, TEA1098 Datasheet - Page 13

• Manufacturer Part Number: TEA1098
• Description: Speech and handsfree IC
• Manufacturer: Philips Semiconductors

Philips Semiconductors
L
Loudspeaker amplifier: pins HFRX, GALS and LSAO
The TEA1098 loudspeaker amplifier has an asymmetrical
input with an input resistance of 20 k between pins HFRX
and GND. It is biased at a voltage of two diodes. Without
output limitation, the input stage can accept signals of up
to 580 mV (RMS) at 2% THD (room temperature).
The gain of the input stage varies according to the
TEA1098 mode. In Rx mode, it has maximum gain; in
Tx mode, it has minimum gain and in Idle mode, it is
halfway between maximum and minimum gain.
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).
Dynamic limiter: pin DLC
The TEA1098 dynamic limiter 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 taken to effect gain reduction
(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
1999 Oct 14
handbook, full pagewidth
OUDSPEAKER CHANNEL
Speech and handsfree IC
Pin numbers in parenthesis apply to the TEA1098H. Pin numbers not in parenthesis apply to the TEA1098TV.
C LSAO
R GALS
C GALS
C DLC
(11)
(12)
(8)
14
15
12
LSAO
DLC
GALS
BB
DYNAMIC
falls below 2.7 V.
LIMITER
V BB
Fig.9 Loudspeaker channel.
V
I
13
logic
to
In Rx mode, the overall gain of the loudspeaker amplifier
can be adjusted from 0 up to 35 dB to suit specific
application requirements. The gain from pin HFRX to pin
LSAO is proportional to the value of R
when R
is connected in parallel with R
low-pass filter.
Volume control: pin VOL
The loudspeaker amplifier gain can be adjusted by the
potentiometer R
potentiometer can be used. Each 1.9 k increase of R
results in a gain loss of 3 dB. The maximum gain reduction
using the volume control is internally limited to the
switching range (see Fig.9).
250 ms). Both attack and release times are proportional to
the value of the capacitor C
The total harmonic distortion of the loudspeaker output
stage, in reduced gain mode, stays below 2% up to 10 dB
(minimum) of input voltage overdrive [providing V
below 580 mV (RMS)].
When the supply voltage falls below an internal threshold
voltage of 2.7 V, the gain of the loudspeaker amplifier is
reduced rapidly (approximately 1 ms). When the supply
voltage rises above 2.7 V, the gain of the loudspeaker
amplifier is increased. By forcing a level lower than 0.2 V
on pin DLC, the loudspeaker amplifier is muted and the
TEA1098 is automatically forced into the Tx mode.
voice switch
to/from
GALS
I
is 255 k . It is recommended that a capacitor
V
envelope
detector
VOL
CONTROL
VOLUME
to
. For logarithmic gain control, a linear
HFRX
MGL343
VOL
DLC
GALS
5
(1)
26
(23)
.
to provide a first-order
R VOL
Product specification
GALS
TEA1098
and is 28 dB
HFRX
VOL
is