TEA1066T Philips Semiconductors (Acquired by NXP), TEA1066T Datasheet - Page 6

• Manufacturer Part Number: TEA1066T
• Description: Versatile Telephone Transmission Circuit With Dialer Interface
• Manufacturer: Philips Semiconductors (Acquired by NXP)

Philips Semiconductors
These outputs may be used for single-ended or for
differential drive, depending on the sensitivity and type of
earpiece used (see Fig.10). Gain from IR to QR+ is
typically 25 dB. This will be sufficient for low-impedance
magnetic or dynamic earpieces, which are suited for
single-ended drive. By using both outputs (differential
drive), the gain is increased by 6 dB and differential drive
becomes possible. This feature can be used when the
earpiece impedance exceeds 450
dynamic, magnetic or piezoelectric earpieces).
The output voltage of the receiving amplifier is specified for
continuous-wave drive. The maximum output voltage will
be higher under speech conditions, where the ratio of peak
to RMS value is higher.
The receiving amplifier gain can be adjusted over a range
of 8 dB to suit the sensitivity of the transducer used.
The gain is set by the external resistor R4 connected
between GAR and QR+.
Two external capacitors, C4 = 100 pF and
C7 = 10
A larger value of C4 may be chosen to obtain a first-order,
low-pass filter. The ‘cut-off’ frequency corresponds with
the time constant R4
Automatic gain control input AGC
Automatic line loss compensation is obtained by
connecting a resistor R6 between AGC and V
automatic gain control varies the microphone amplifier
gain and the receiving amplifier gain in accordance with
the DC line current.
The control range is 6 dB. This corresponds with a line
length of 5 km for a 0.5 mm diameter copper twisted-pair
cable with a DC resistance of 176 /km and an average
attenuation of 1.2 dB/km.
Resistor R6 should be chosen in accordance with the
exchange supply voltage and its feeding bridge resistance
(see Fig.11 and Table 1). Different values of R6 give the
same ratio of line currents for start and end of the control
range.
If automatic line loss compensation is not required, AGC
may be left open. The amplifiers then all give their
maximum gain as specified.
Power-down input PD
During pulse dialling or register recall (timed loop break)
the telephone line is interrupted, as a consequence it
provides no supply for the transmission circuit and the
peripherals connected to V
1996 Apr 04
Versatile telephone transmission circuit
with dialler interface
C4 = 1 nF, are necessary to ensure stability.
C4.
CC
. These gaps have to be
(high-impedance
EE
. This
6
bridged by the charge in the smoothing capacitor C1.
The requirements on this capacitor are relaxed by applying
a HIGH level to the PD input during the time of the loop
break, which reduces the supply current from typically
1 mA to typically 55 A.
A HIGH level at PD further disconnects the capacitor at
REG, with the effect that the voltage stabilizer will have no
switch-on delay after line interruptions. This results in no
contribution of the IC to the current waveform during pulse
dialling or register recall. When this facility is not required
PD may be left open.
Side-tone suppression
Suppression of the transmitted signal in the earpiece is
obtained by the anti-side-tone network consisting of
R1//Z
compensation is obtained when the following conditions
are fulfilled:
If fixed values are chosen for R1, R2, R3, and R9, then
condition (1) will always be fulfilled, provided that
suppression, condition (2) has to be fulfilled, resulting in:
Z
k
Scale factor k (dependent on the value of R8) must be
chosen to meet the following criteria:
1. Compatibility with a standard capacitor from the E6 or
2.
3.
In practice, Z
type; consequently, an average value has to be chosen for
Z
with which Z
Example: The balanced line impedance Z
the optimum suppression is preset can be calculated by:
Assume Z
5 km line of 0.5 mm diameter, copper, twisted-pair cable
matched to 600
then R8 = 390 ; Z
The anti-side-tone network for the TEA1060 family shown
in Fig.4 attenuates the signal received from the line by
32 dB before it enters the receiving amplifier.
R9 R2
Z
R8//Z
bal
bal
bal
(R8/R1).
. The suppression further depends on the accuracy
E12 range for Z
Z
Z
line
(R8/R1) Z
bal
bal
bal
Z
, R2, R3, R8, R9 and Z
bal
//R8 << R3
+ R8 >> R9.
=
line
< R3. To obtain optimum side-tone
+
R1 R3
bal
line
= 210
R8
/k equals the average line impedance.
line
varies greatly with line length and cable
(176 /km; 38 nF/km). When k = 0.64,
=
bal
bal
+
k
Z
+ (1265 /140 nF), representing a
= 130
line
R8//Z
Z
line
Z
, where k is a scale factor:
bal
line
+ (820 //220 nF).
bal
+
(see Fig.14). Maximum
R1
Product specification
TEA1066T
bal
at which
(1)
(2)