TEA1098 Philips Semiconductors, TEA1098 Datasheet - Page 17

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

halfpage
Philips Semiconductors
Table 1 TEA1098 modes
The switch-over timing can be set by capacitor C
the Idle mode timing can be set by capacitor C
resistor R
is 220 nF and R
time from Tx to Rx mode or vice-versa of approximately
13 ms (580 mV swing on pin SWT). The switch-over time
from Idle mode to Tx or Rx mode is approximately 4 ms
(180 mV swing on pin SWT).
The switch-over time, from Rx or Tx mode to Idle mode is
equal to 4
(Idle mode time).
The DLC input overrides the decision logic. When the
voltage on pin DLC falls below 0.2 V, the capacitor C
is discharged by 10 A which selects Tx mode.
Voice switch: pins STAB and SWR
Figure 13 is a diagram of the voice switch. With a voltage
on pin SWT, the TEA1098 voice switch regulates the gains
1999 Oct 14
< 180
0
> 180
Speech and handsfree IC
(1) C = constant.
Pin numbers in parenthesis apply to the TEA1098H.
Pin numbers not in parenthesis apply to the TEA1098TV.
V
volume
control
SWT
from
IDT
. In the basic application given in Fig.19, C
R
DUPLEX CONTROLLER
microphone
V
IDT
amplifier
IDT
G vtx
VOICE SWITCH
IDT
to
C
loudspeaker
(mV)
SWT
Fig.13 Voice switch.
amplifier
is 2.2 M . This enables a switch-over
G vrx
to
and is approximately 2 seconds
SWT
from
C
(1)
Tx mode
Idle mode
Rx mode
STAB 24 (21)
SWR
MGL346
25 (22)
MODE
R STAB
R SWR
SWT
SWT
and
SWT
and
SWT
17
of the transmit and the receive channels so that the sum of
both is held constant.
In Tx mode, the microphone amplifier is at maximum gain
and the loudspeaker amplifier is at minimum gain.
In Rx mode, their gains are the opposite. In Idle mode,
both microphone and loudspeaker amplifiers are midway
between maximum and minimum gain.
The difference between the maximum and minimum gain
is called the switching range. This range is determined by
the ratio of resistors R
between 0 and 52 dB. Resistor R
which sets an internally used reference current. In the
basic application diagram (Fig.19), resistor R
365 k which results in a switching range of 40 dB.
The switch-over behaviour is illustrated in Fig.14.
In Rx mode, the gain of the loudspeaker amplifier can be
reduced using the volume control. At the same time, the
gain of the microphone amplifier increases, since the voice
switch keeps the sum of the gains constant (see dashed
curves in Fig.14). However, in Tx mode, the volume
control has no effect on the gains of the microphone or
loudspeaker amplifiers. Consequently, the switching range
is reduced when the volume is reduced. At maximum
reduction of volume, the switching range is 0 dB.
handbook, halfpage
G vtx, G vrx
(10 dB/div)
400
Tx mode
Fig.14 Switch-over behaviour.
G vtx
G vrx
200
SWR
to R
idle
mode
0
STAB
STAB
and is adjustable
V SWT
Product specification
should be 3.65 k
200
Rx mode
TEA1098
V IDT (mV)
MGM305
SWR
400
is
R VOL
11400
7600
3800
0
0
3800
7600
11400
( )