Philips Semiconductors
Product specification
Low voltage versatile telephone
transmission circuit with dialler interface
Set impedance
In the audio frequency range, the dynamic impedance is
mainly determined by the R
CC
resistor. The equivalent
impedance of the circuit is illustrated in Fig.7.
Microphone amplifier (pins MIC+ and MIC−)
The TEA1110A has symmetrical microphone inputs.
The input impedance between pins MIC+ and MIC− is
64 kΩ (2
×
32 kΩ). The voltage gain from pins MIC+/MIC−
to pin LN is set at 43.7 dB (typ).
Automatic gain control is provided on this amplifier for line
loss compensation.
Receiving amplifier (pins IR, GAR and QR)
The receiving amplifier has one input (IR) and one output
(QR). The input impedance between pin IR and pin V
EE
is
20 kΩ. The voltage gain from pin IR to pin QR is set at
33 dB (typ). The gain can be decreased by connecting an
external resistor R
GAR
between pins GAR and QR; the
adjustment range is 14 dB. Two external capacitors C
GAR
(connected between GAR and QR) and C
GARS
(connected
between GAR and V
EE
) ensure stability. The C
GAR
capacitor provides a first-order low-pass filter. The cut-off
frequency corresponds to the time constant
C
GAR
×
(R
GARint
// R
GAR
). R
GARint
is the internal resistor
which sets the gain with a typical value of 125 kΩ.
The condition C
GARS
= 10
×
C
GAR
must be fulfilled to
ensure stability.
The output voltage of the receiving amplifier is specified for
continuous wave drive. The maximum output swing
depends on the DC line voltage, the R
CC
resistor, the I
CC
current consumption of the circuit, the I
P
current
consumption of the peripheral circuits and the load
impedance.
Automatic gain control is provided on this amplifier for line
loss compensation.
Automatic gain control (pin AGC)
The TEA1110A performs automatic line loss
compensation. The automatic gain control varies the gain
of the microphone amplifier and the gain of the receiving
amplifier in accordance with the DC line current.
The control range is 5.9 dB (which corresponds
approximately to a line length of 5 km for a 0.5 mm
diameter twisted-pair copper cable with a DC resistance of
176
Ω/km
and an average attenuation of 1.2 dB/km).
The IC can be used with different configurations of feeding
bridge (supply voltage and bridge resistance) by
connecting an external resistor R
AGC
between pins AGC
1997 Apr 22
6
TEA1110A
and V
EE
. This resistor enables the I
start
and I
stop
line
currents to be increased (the ratio between I
start
and I
stop
is
not affected by the resistor). The AGC function is disabled
when pin AGC is left open-circuit.
Mute function (pin MUTE)
The mute function performs the switching between the
speech mode and the dialling mode. When MUTE is LOW,
the DTMF input is enabled and the microphone and
receiving amplifiers inputs are disabled. When MUTE is
HIGH, the microphone and receiving amplifiers inputs are
enabled while the DTMF input is disabled. A pull-up
resistor is included at the input.
DTMF amplifier (pin DTMF)
When the DTMF amplifier is enabled, dialling tones may
be sent on line. These tones can be heard in the earpiece
at a low level (confidence tone).
The TEA1110A has an asymmetrical DTMF input.
The input impedance between DTMF and V
EE
is 20 kΩ.
The voltage gain from pin DTMF to pin LN is 25.3 dB.
The automatic gain control has no effect on the DTMF
amplifier.
handbook, halfpage
2.5
MBE783
IP
(mA)
2
1.5
1
0.5
(2)
(1)
0
0
1
2
3
VCC (V)
4
(1) With R
VA
resistor.
(2) Without R
VA
resistor.
Fig.5
Typical current I
P
available from V
CC
for
peripheral circuits at I
line
= 15 mA.
PHILIPS [ NXP SEMICONDUCTORS ]
