TEA1068 Ver la hoja de datos (PDF) - Philips Electronics
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TEA1068 Datasheet PDF : 24 Pages
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Philips Semiconductors
Versatile telephone transmission circuit
with dialler interface
Product specification
TEA1068
If fixed values are chosen for R1, R2, R3 and R9, then
condition (1) will always be fulfilled, provided that
R8//Zbal << R3. To obtain optimum side-tone
suppression, condition (2) has to be fulfilled, resulting in:
Zbal = (R8/R1) Zline = k × Zline, where k is a scale factor:
k = (R8/R1).
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
E12 range for Zbal
2. Zbal//R8<< R3 to fulfil condition (1) and thus
ensuring correct anti-side-tone bridge operation
3. Zbal + R8>> R9 to avoid influencing the transmitter
gain.
In practice, Zline varies greatly with the line length and
cable type; consequently, an average value has to be
chosen for Zbal, thus giving an optimum setting for short or
long lines.
Example: the balanced line impedance (Zbal) at which the
optimum suppression is preset can be calculated by:
Assume Zline = 210 Ω + (1265 Ω/140 nF), representing a
5 km line of 0.5 mm diameter, copper, twisted-pair cable
matched to 600 Ω (176 Ω/km; 38 nF/km). When k = 0.64,
then R8 = 390 Ω; Zbal = 130 Ω + (820 Ω//220 nF).
The anti-side-tone network for the TEA1060 family shown
in Fig.5 attenuates the signal received from the line by
32 dB before it enters the receiving amplifier.
The attenuation is almost constant over the whole audio
frequency range.
Figure 6 shows a conventional Wheatstone bridge
anti-side-tone circuit that can be used as an alternative.
Both bridge types can be used with either resistive or
complex set impedances.
handbook, full pagewidth
LN
Zline
R1
VEE
R9
R2
IR
im
R3
R8
SLPE
Zbal
Rt
MSA500
Fig.5 Equivalent circuit of TEA1060 family anti-side-tone bridge.
1996 Apr 23
7
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