U4090B Datasheet, PDF (13/34 Pages) TEMIC Semiconductors – Monolithic Integrated Feature Phone Circuit

ATAFS (dB)
ATAFS_m
ATAFS_a
RATAFS
RATAFS
U4090B
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not usable
GSA_o
GSA_a
36 dB
GSA (dB)
Figure 8. Reducing speaker amplifier gain results in an equal reduction of AFS attenuation
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When Power Down is activated (during pulse dialing), all
of the line current flows through the short circuiting
transistor QS (see figure 6). As long as IL is above typ.
1.6 mA, output LIDET is low. This comparator does not
use hysteresis.
IL
LIDET
PD
Figure 9. Line detection with two comparators for speech mode
and pulse dialling
LIDET
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Line detection (LIDET)
The line current supervision is active under all operating
conditions of the U4090B. In speech mode
(PD = inactive) the line current comparator uses the same
thresholds as the comparator for switching off the entire
speaker amplifier. The basic behaviour is illustrated in
figure 13. Actual values of ILON/ILOFF vary slightly
with the adjustment of the DC-characteristics and the
selection of the internal line impedance.
ILOFF
ILON
IL
Figure 10. Line detection in speech mode with hysteresis
TELEFUNKEN Semiconductors
Rev. C1, 28-Oct-96
Preliminary Information
13 (34)