Philips Semiconductors
Product specification
Low voltage versatile telephone
transmission circuit with dialler interface
SIDETONE SUPPRESSION
TEA1110A
handbook, halfpage
RCCint
VCC
The TEA1110A anti-sidetone network comprising
R
CC
//Z
line
, R
ast1
, R
ast2
, R
ast3
, R
SLPE
and Z
bal
(see Fig.8 )
suppresses the transmitted signal in the earpiece.
Maximum compensation is obtained when the following
conditions are fulfilled:
PERIPHERAL
CIRCUIT
VCCO
Irec
R
SLPE
×
R
ast1
=
R
CC
× (
R
ast2
+
R
ast3
)
IP
MBE792
(
R
ast2
× (
R
ast3
+
R
SLPE
) )
k
=
----------------------------------------------------------------------
-
(
R
ast1
×
R
SLPE
)
Z
bal
=
k
×
Z
line
The scale factor k is chosen to meet the compatibility with
a standard capacitor from the E6 or E12 range for Z
bal
.
In practice, Z
line
varies considerably with the line type and
the line length. Therefore, the value of Z
bal
should 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
bal
and the impedance of the average line.
The anti-sidetone network for the TEA1110A (as shown in
Fig.12) attenuates the receiving signal from the line by
32 dB before it enters the receiving amplifier.
The attenuation is almost constant over the whole audio
frequency range.
A Wheatstone bridge configuration (see Fig.9) 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.
VEE
Fig.6 V
CC
supply voltage for peripherals.
handbook, halfpage
LN
RP
REG
CREG
4.7
µF
RCC
619
Ω
VCC
CVCC
100
µF
MBE788
LEQ
Vref
SLPE
RSLPE
20
Ω
VEE
L
eq
= C
REG
×
R
SLPE
×
R
P
.
R
P
= internal resistance.
R
P
= 15.5 kΩ.
Fig.7 Equivalent impedance between LN and V
EE
.
1997 Apr 22
7
PHILIPS [ NXP SEMICONDUCTORS ]
