PBL 3852
+
PBL
3852
R1
R2
PBL
3852
PD
>Ref.
18
PD
18
14
> Ref. (1.16V)+diode
in
2
IPD
or
C1
TO
-L
39Ω
in
Digital control
Linear control. Is effective only at line
currents <10mA. (also dependent of
DC-characteristic)
Figure 20. Power down input.
PBL
PBL
PBL
PBL
3852
3852
IMute
I
Mute
3852
MO
3852
6
11
14 11
MO
17
16
Mute
-L
Rx
V
Mute
14
-L
14
V
Mute
-L
100
Ω
C
15
Muting
points
C8
Microphone mute only
Receiver mute only.
Figure 21. Mute input.
Mute function
DC-control DCC input
will cause a ”click ” in the earphone. This
can be softened with a slower mute signal
flank. If the second approach, grounding
before the input capacitor is chosen, the
grounding has to be low ohmic in order to
render a high attenuating mute.
The circuit has a mute function at pin 6.
By sourcing current into this pin will cut off
the gain in the microphone amplifier
(attenuation min. 60dB) and decrease the
gain in the receiver amplifier to reach the
confidence tone level at DTMF-dialling.
The receiver mute is ≈-40dB down from
the unmuted value to satisfy those who
keep the handset close to the ear at
dialling. For users who keep the handset
from the ear the confidence tone level is
too low. To alter the level, a signal can be
taken from DTMF generator output to
receiver input before the capacitor C8.
The added impedance to this point will
hardly disturbe the signal condition in
active speech mode. The microphone
amplifier only, can be muted by draining
current from the output pin MO. See fig.
21. In case it is required to mute the
receiver only, it can be done by shorting
the receiver input to ground before or
after the input capacitor. Shorting the
input pin to ground (does not have to be
absolute ground) actuates a mute by
driving the amplifier into saturation thus
blocking the signal path and rendering a
mute with high attenuation but will cause
a DC-level shift at output which in its turn
The circuit has a DC- control input that
can adjust the DC-characteristic. When
a current is sourced into this pin the line
voltage will increase for a given line
current. This will enable an increased
negative swing for both the transmitter
and receiver at low line currents. If this
function is used together with LD - dialling
care must be taken that the DC-level of
the pulses is according to the
specification. The two adjustment paths
shown in the fig. 33 will have following
functions: Using R20 will alter the
adjustment with changing line current
where by using the path with R21 renders
a fix adjustment. If the input is not used it
can be left open or grounded to pin 14.
DTMF (Dual tone multi -
frequency) input
The DTMF signal is added between the
microphone and transmitter amplifiers, an
input that can be seen as a summing
point for signals to be transmitted to the
line. See fig. 32. Dialling connected like
this will render a confidence tone in the
receiver at mute condition.
Start up circuit
The circuit contains a start up device
which function is to fast charge the
capacitor C9 when the circuit goes into
hook- off condition. The fast charge circuit
is a thyristor function between pins 1 and
4 that will stop conducting when the
current drain at pin 4 is lower than ≈ 700
µA + the internal current consumption.
( about 1 mA) This circuit can not
Power supplies DC1, DC2,
V+C and VPh (see fig. 22)
The PBL 3852 generates its own DC
supply V
dependent of line current with
an internal shunt regulator. This regulator
+C
senses the line voltage V via R19 and
L
line current via R7 in order to set the
retrigger before the voltage level at C9
correct V
so the circuit can generate
the required DC characteristic for a given
+C
14
ERICSSON [ ERICSSON ]
