TEA1118 Philips Semiconductors, TEA1118 Datasheet - Page 10

• Manufacturer Part Number: TEA1118
• Description: Versatile cordless transmisssion circuit
• Manufacturer: Philips Semiconductors

Philips Semiconductors
Automatic Gain Control (pin AGC)
The TEA1118 and TEA1118A perform automatic line loss
compensation. The automatic gain control varies the gain
of the transmit amplifier and the gain of the receive
amplifier in accordance with the DC line current.
The control range is 5.8 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 /km and an average attenuation of 1.2 dB/km).
The ICs can be used with different configurations of
feeding bridge (supply voltage and bridge resistance) by
connecting an external resistor R
and V
currents to be increased (the ratio between I
not affected by the resistor). The AGC function is disabled
when pin AGC is left open-circuit.
DTMF amplifier (pin DTMF; TEA1118A only)
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 TEA1118A has an asymmetrical DTMF input.
The input impedance between DTMF and V
The voltage gain from pin DTMF to pin LN is 17.4 dB.
The automatic gain control has no effect on the DTMF
amplifier.
Mute function (pin MUTE; TEA1118A only)
The mute function performs the switching action between
the speech mode and the dialling mode. When MUTE is
LOW or open-circuit, the transmit and receive amplifiers
inputs are enabled while the DTMF input is disabled,
depending on the TMUTE level. When MUTE is HIGH, the
DTMF input is enabled and the transmit and receive
amplifiers inputs are disabled.
MUTE and TMUTE levels for different modes (TEA1118A only)
Table 1 Required MUTE and TMUTE levels to enable the different possible modes
Note
1. X = don’t care.
1997 Jul 14
Speech
DTMF dialling
Transmit mute
Versatile cordless transmisssion circuit
MODE
EE
. This resistor enables the I
TRANSMIT
on
off
off
AGC
start
between pins AGC
RECEIVE
and I
on
off
on
start
EE
stop
CHANNEL
is 20 k .
and I
line
stop
is
DTMF
on
on
10
off
Sidetone suppression
The TEA1118 and TEA1118A anti-sidetone network
comprising R
(see Fig.12) suppresses the transmitted signal in the
earpiece. Maximum compensation is obtained when the
following conditions are fulfilled:
The scale factor k is chosen to meet the compatibility with
a standard capacitor from the E6 or E12 range for Z
In practice, Z
the line length. Therefore, the value chosen for Z
be for an average line length which gives satisfactory
sidetone suppression with short and long lines.
The suppression also depends on the accuracy of the
match between Z
line.
The anti-sidetone network for the TEA1118 and
TEA1118A (as shown in Fig.16) attenuates the receive
signal from the line by 32 dB before it enters the receive
amplifier.
The attenuation is almost constant over the whole audio
frequency range.
A Wheatstone bridge configuration (see Fig.13) may also
be used.
More information on the balancing of an anti-sidetone
bridge can be obtained in our publication “Applications
Handbook for Wired Telecom Systems, IC03b” , order
number 9397 750 00811.
R
k
Z
bal
SLPE
=
---------------------------------------------------------------------- -
=
R
k Z
CONFIDENCE
ast2
R
ast1
R
TONE
line
line
CC
ast1
off
on
off
R
//Z
=
varies considerably with the line type and
ast3
bal
R
line
R
CC
and the impedance of the average
, R
SLPE
+
R
TEA1118; TEA1118A
ast1
SLPE
R
, R
ast2
MUTE
HIGH
LOW
LOW
ast2
+
, R
R
ast3
ast3
Product specification
, R
SLPE
TMUTE
HIGH
LOW
and Z
X
bal
(1)
should
bal
bal
.