May 1996
PBL 3853
Universal Speech Circuit
Description
The PBL 3853 is a biopolar integrated speech circuit with specific parameters making
it highly suitable to be used as a line interface and speech circuit in a telephone line
powered electronic payphone. Emphasis has been put on low current consumption in
the IC thus facilitating that a greater part of the available line current can be used to
power other electrical functions in the design. From a minimum line current of
16 mA, 12 mA at 4.5 V can be used to power auxiliary functions. The circuit can
optionally create an active impedance towards the telephone line, set by external
passive components, to reduce the current consumption for the transmitted signal.
The circuit is designed to be used with a low impedance dynamic microphone but can
be used with an electret type as well. The receiver drives a low ohm dynamic
transducer directly. External clamping diodes are required on the receiver output.
Both transmitter and receiver can be muted separately (receiver cut off). Line length
regulation of the gain is possible in both receiver and transmitter. It is also possible to
use the circuit without regulation. Payphone tones and confidence tone in the recei-
ver at DTMF dialling can be injected directly into the receiver amplifier where their
levels are not affected by line length regulation and without the signal going out on
the line. All pin numbers refer to DIP package unless otherwise noted.
Key Features
•
Low own current consumption
•
Can operate both with active and
passive impedance towards the line
•
Derives a high current from the line
for auxiliary functions, 12 mA at
16 mA line current
•
Separate mute inputs for transmitter
and receiver (receiver cut off)
•
Line length regulation possible (line
loss compensation
•
Comes in 18 pin DIP and 20-pin SO
package
•
High line current operation, max.
130 mA
•
Especially suitable for payphone
applications
•
DTMF - confidence tone input
•
Excellent RFI performance
1
9
PBL 3853
5
4
10
+V
-
+
-
12
-
8
18
P
18-pin plastic DIP
MA
Rx
13
Tx
B
P
B
L
38
20-pin plastic SO
+
16
6
14
11
3
2
17
15
Figure 1. Block diagram. Pin numbers in all figures refer to DIP package.
53
L
38
5
+
3
7
ERICSSON [ ERICSSON ]
