PBL 3726/18A
Functional Description
+ Line
General
AR
1
3
The gain of the transmitting and
receiving amplifiers are continuously
and equally changed with the line
length. The starting point for the gain
regulation is externally set. The gain
regulation can be cut-off externally, see
table under gain regulation below.
The outputs of the transmitting and
receiving amplifiers have internal
limitations of the output amplitudes.
The circuit includes a temperature
independent voltage reference used for
regulation of the DC line voltage, DC-
supply for external use and for the
transmitting and receiving gain
AT
AM
2
4
Transmitting
cut off
- Line
Mute
Figure 6. Block interconnections.
1
+Line
regulation. The DC line voltage is very
fast settled to its final value with a
minimum of overshoot.
1.2V
+
The circuit uses a minimum of
V
V
external components. In a normal
practical case only 7 external capaci-
tors of which only two are electrolytic/
tantalum filter capacitor. One of the
other capacitors is needed as radio
interference suppression capacitor
over the line, one capacitor in the side-
tone balancing network and one
capacitor for low frequency cut-off in
each of the transmitting and receiving
amplifiers. The frequency response is,
except for that, flat for both amplifiers.
The circuit will with external compo-
nents get a very good return loss
behaviour, both against purely resistive
lines as for instance 600 ohm and
against complex networks as 900 ohm
in parallel with 30 nF.
DC
DC
-
0-470Ω
8
1
2
0-470Ω
9
R
DC1
DC2
15kΩ
15kΩ
+
+
7
4.7-47
µF
R
14
Figure 7. DC regulator for external CMOS devices. 18-pin DIP pin numbers.
KEYPAD
3
3
1
1
2
5
8
0
4
7
6
9
#
1
PBL 3726/18
10
DTMF
output
17
AD
AM
Uz = 12 V
220 nF
AT
AR
DTMF
dialer
(CMOS type)
12
13
Telephone
line
18
DC
9
+
10 Ω
8
7
6
5
11
3
2
15 16
14
4
C6
R10
62 k
Sense Input
100 nF
C3
R4
18 k
47 nF
R7
Control output
R1
910 Ω
6 k 2
DC
R3
910 Ω
C2
∞
R11
R8
560 Ω
15 nF
Mute
out
R13 R15
C1
47 µF
R5
22 k
R6
75 Ω
R2
∞
C5
100 nF
47 µF
R9
11 k
11 k 10 Ω
GND
Figure 8. Typical tone dialling telephone. Pinning DIP package.
5
ERICSSON [ ERICSSON ]
