PBL
1996
February
3881
PBL 3881
Voice-switched
Speakerphone Circuit
Description
The PBL 3881 contains all the necessary circuitry, amplifiers, detectors, comparators
and control functions to implement a high performance, voice-switched,
loudspeaking, ”hands-free ” telephone. The gain dynamics (attenuation between
channels) is continuously adjustable (0-50 dB) via a separate pin. A background
noise detector in the transmitting channel reduces the influence of continuous noise
signals.
The PBL 3881 is designed for telephone line powered applications. The circuit
contains a transformerless power amplifier with a current supply circuitry that
eliminates the need of inductors (patented). Automatic volume attenuation in the
power amplifier extends the operating range at low line currents.
Filtering of the signals in both transmitter and receiver channels is possible.
Optional AGC function can be implemented into the receiver channel.
All pinnumbers refer to 22-pin DIP-package unless otherwise noted.
Key Features
•
•
•
•
•
•
•
21
17
19
Adjustable gain range in the
attenuated channel (0 - 50 dB).
Direct telephone line powered solution
(patented).
Low power consumption, 2.2 mA at
3.2 V (typical).
Direct drive of an 25 - 50 ohm
loudspeaker.
22-pin dual in-line plastic, 24-pin SO
and 28-pin PLCC encapsulation.
Background noise compensation in the
transmitting channel.
Good noise performance.
Fully accessible in - and outputs of the
channel input amplifiers.
Minimum of external components
needed for function.
•
•
20
–
+
22
5
14
PBL 3881
–
F3
+
Control
+
–
F6
28 pin PLCC
10
15
PB
88
L3
1
24 pin SO
+
F2
4
3
1
2
–
F1
+
7
6
8
9
Ref.
–
F4
12
+
13
PB
22 pin DIP
Figure 1. Block diagram.
1
L
11
38
81
F5
P
3 B
8 L
8
1
18
16
ERICSSON [ ERICSSON ]
