April 1996
PBL 3852
PBL 3852
Universal Transmission Circuit
Description
The PBL 3852 is an universal transmission circuit in bipolar technology that performs
all the speech and line interface functions required to implement an electronic
telephone set suitable for the majority of existing telephone network requirements.
Easy adaptation of the DC-mask to different line feed systems. A summing point
for auxiliary signals to be transmitted like DTMF and hands-free audio signal. The
PBL 3852 has a low current consumption that enables the circuit to work with
reduced performance down to 2.1 volts (4.8 mA) across the circuit. The low current
consumption for a speech circuit is essential in telephone line powered handsfree
designs required to work at long line lengths. The PBL 3852 is especially suitable to
be used with Ericsson handsfree circuits like PBL 3786, PBL 3786/2, PBL 3881 and
PBL 3880 thanks to a specific interfacing arrangement.
The transmitting and receiving gains can be regulated in order to compensate for
the attenuation of the signals due to increasing attenuation with increasing line length.
It is also possible to limit high transmitting signal levels (soft clipping) thus preventing
excessive distortion caused by signal clipping. The gain regulation is set with discrete
external components.
The circuit is easily adapted to different markets by setting the application depend-
ent parameters individually in certain order, this preventing the interaction between
the same. PBL 3852 has up to four different power supplies to feed microphones,
auxiliary circuits and functions.
All pin numbers in this paper refer to DIP package.
Key Features
•
•
Generates its own supply from the
telephone line
Adaptive to all types of telephone line
feeding systems (i.e. 48V 2x200Ω,
60V 2x 600Ω, 48V 2x800Ω)
Operates down to 2.1V (excl. polarity
bridge)
Adjustable DC-characteristic to the line
Few inexpensive external components
to function
Easy adaptation for various market
needs
Dialler interface with DC-supply, mute,
power -down and DTMF-input
Confidence tone in the receiver at
DTMF-dialling
”Soft clipping” that prevents distortion
at high transmit signal levels
Balanced microphone input for dyna-
mic, and electret microphones
Balanced receiver output for dynamic
and magnetic receiver elements
Transmitter and receiver gain regula-
tion for automatic loop loss compen-
sation (disabled in mute mode)
Four separate DC supplies for different
requirements
High gain of the receiver facilitates
volume control function
Microphone cut-off function possible
by a switch
All gain and frequency setting networks
in Rx, Tx and side tone are referred to
ground
Excellent RFI performance
•
•
•
•
•
•
•
•
•
•
•
(+Line)
•
•
6
13
+
5
1
17
•
12
+
-
+
Telephone
line
16
14
4+
•
Ref.
18
DC
supply
DC
supply
9
8
11
3
2
7
PBL 3852
10
A.
Ref.
15
+
+
+
+
P
B.
B
L
38
18-pin plastic DIP 20-pin plastic SO
Power
down
DC1
DC2
52
C.
(-Line)
A. Dynamic limiter
B. Sidetone network
C. Gain regulation with line length
Figure 1. Functional diagram.
1
P
B
DTMF
L
38
52
ERICSSON [ ERICSSON ]
