October 1999
PBL 388 12
PBL 388 12
Voice-switch circuit for
Handsfree speakerphone TAM
Description
The PBL 388 12 contains all the necessary circuitry, amplifiers, detectors, comparators
and control functions to implement a high performance, voice-switched, ”hands-free ”
function in an answering machine. The gain dynamics (attenuation between channels)
is settable (25dB or 50dB) via CTR pin that also control two mute levels. A background
noise detector in the transmitting channel reduces the influence of continuous noise sign-
als.
The PBL 388 12 is designed for answering machines that are either powered from the
telephone line or from a mains powered dc. supply.
Filtering of both the audio and control signals in both transmitter and receiver channels
possible.
An external loudspeaker amplifier has to be used, normally the same as used for the
answering machine.
All figures in this paper refer to 16-pin SO package.
Key Features
• Settable gain dynamics (25 or 50
dB).
• Low power consumption, totally
1.0mA at 3.3V typical.
• Background noise compensation in
the transmitting channel with hold
function.
• Exellent noise performance.
• Both channel input amplifiers have
balanced inputs.
• Minimum of external components
needed for function.
• 16-pin SO and 18-pin DIP
encapsulation.
1
5
PBL 388 12
F3
Control
F6
12
16
4
6
15
13
11
P
B
L
38
8
16-pin SO
+
F2
F5
–
3
F1
+
8
7
9
10
2
F4 +
Ref.
P
14
B
L
18-pin DIP
Figure 1. Block diagram. ( SO - package )
38
8
12
12
1
ERICSSON [ ERICSSON ]
