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PDF PBL3852 Data sheet ( Hoja de datos )
| Número de pieza | PBL3852 | |
| Descripción | Universal Transmission Circuit | |
| Fabricantes | Ericsson | |
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PABpLril31895926
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.
(+Line)
6
13
+
12
5
Ref. DC
supply
DC
supply
18 9 8 11
3
1
+
PBL 3852
Ref.
27
10 15
17
-
+
16
14 4 +
Telephone
line
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
Power
down
DC1 DC2
A.
++
B.
+
+
DTMF
C.
(-Line)
A. Dynamic limiter
B. Sidetone network
C. Gain regulation with line length
Figure 1. Functional diagram.
18-pin plastic DIP 20-pin plastic SO
1
1 page  
PBL 3852
Functional Description
Design procedure
+Line
1. Set the circuit impedance to the line,
either 600Ω or complex. (R19 and C9).
C9 should be big enough to give low
impedance compared with R19 in the
telephone speech frequency band.
Too large C9 will make the start-up
slow.
PBL 3852
1
4
a)
R19
b)
c)
2. Set the DC-characteristic that is
required in the PTT specification or in
case of a system telephone in the PBX
32
specification (R7). There are also
internal circuit dependent requirements
like supply voltages etc.
C10
R7
3. Set the attac point where the line length
regulation is supposed to cut in
(R14,R15 and R16). Note that in some
countries the line length regulation is
not allowed. In most cases the
end result is better and more readily
Figure 6. AC-impedance.
achieved by using the line length
regulation (line loss compensation)
Impedance to the line
than without.
The AC- impedance to the line is set by
4. Set the transmitter gain, regulation and C10, R19 and C9. Fig. 6. The circuits
frequency response. See text for the relatively high (≈ 20k with R7 = 75Ω)
dynamic limiting feature.
5. Set the receiver gain and frequency
response. See text how to limit the
max. swing to the earphone.
parallel impedance will influence it to
some extent. At low frequencies the
influence of the C9 can not be neglected.
Series resistance of the C9 that is
dependent on temperature and quality will
6. Adjust the side tone balancing network. cause that some of the line signal will
7. Set the RFI suppression components enter pin 4 and generate a closed loop in
in case necessary. In two piece
the transmitter amplifier that will create an
telephones the often ”helically” wound active impedance thus lowering the
cord acts as an aerial where especially impedance to the line. The impedance at
the microphone input with its high gain high frequencies is set by C10 that also
and input impedance is the more
acts as a RFI suppressor.
sensitive.
In many specifications the impedance
towards the line is specified as a complex
network. See fig. 6. In case a) the error
+Line
R19
1
PBL 3852
+
-
2
R7
Ref=1.16V
4
- I pin5
+
C9
5
I pin5
R20
R21
DC-
supply
9
DC1
R3 +
C2
Figure 7. System of DC-Characteristic.
Rs
≈1Ω
+
C9
Example:
The complex network
220Ω + 820Ω//115nF
-Line
signal entering pin 4 is set by the ratio
≈Rs/R19 (909Ω), where in case b) the
ratio at high frequency will be Rs/220Ω
because the 820Ω resistor is bypassed by
a capacitor. To help up this situation the
complex network capacitor is connected
directly to ground, case c) making the
ratio Rs/220Ω+820Ω and thus lessening
the error signal. Conclusion: Use case c)
when complex impedance is specified.
DC - characteristic
The DC - characteristic that a telephone
set has to fulfill is mainly given by the
network administrator.Following para-
meters are useful to know when the DC
behaviour of the telephone is to be set:
• The voltage of the feeding system
• The line feeding resistance 2 x.... ohms
• The maximum current from the line at
zero line length
• The min. current at which the telephone
has to work (basic function)
• The lowest and highest voltage
permissible across the telephone set.
• The highest voltage that the telephone
may have at different line currents is
normally set by the network owners
specification. The lowest voltage for the
telephone is normally set by the
different voltages that are needed for
the different parts of the telephone. For
ex. for transmitter output amplifier,
receiver output amplifier, dialler,
speech switching and loudspeaker
amplifier in a handsfree telephone etc.
5
5 Page 
PBL 3852
(dB) ∆ Transmitter gain
0
-1
-2
-3
-4
-5
-6 Full regulation
-7
-8
Same amount of
regulation as in the
receiver
DC pin GR
1.00
1.05
1.10
at P km
1.15
1.20
1.25
at 0 km
(V)
Figure 15. Transmitter line length regulation. How to determine the voltage at pin GR for a certain line length 0-P at a certain
regulation of gain.
(dB) ∆ Receiver gain
0
-1
-2
-3
-4
-5
-6
1.00 1.05 1.10
Figure 16. Receiver line length regulation.
1.15
1.20
DC pin GR
1.25
(V)
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet PBL3852.PDF ] | |
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