Features
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Adjustable DC Characteristics
Adjustable Transmit and Receive Gain
Symmetrical Input of Microphone Amplifier
Anti-clipping in Transmit Direction
Automatic Line-loss Compensation
Built-in Ear Protection
DTMF and MUTE Input
Adjustable Side Tone Suppression Independent of Sending and Receiving
Amplification
Integrated Amplifier for Loud-hearing Operation
Anti-clipping for Loudspeaker Amplifier
Improved Acoustical Feedback Suppression
Selectable Line Impedance
Voice Switch
Supply Voltages for All Functional Blocks of a Subscriber Set
Operation Possible from 10-mA Line Current
Monolithic
Integrated
Feature Phone
Circuit
U4089B-M
Benefits
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Complete System Integration of Analog Signal Processing on One Chip
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Very Few External Components
Applications
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Feature Phones
Answering Machines
Fax Machines
Speaker Phones
Description
The telephone circuit U4089B-M is a linear integrated circuit for use in feature phones,
answering machines and fax machines. It contains the speech circuit, side tone
equivalent and ear protection rectifiers. The circuit is line-powered and contains all
components necessary for the amplification of signals and adaptation to the line.
An integrated voice switch with a loudspeaker amplifier enables loud-hearing or
hands-free operation. With an anti-feedback function, acoustical feedback during loud-
hearing can be reduced significantly. The generated supply voltage is suitable for a
wide range of peripheral circuits.
Figure 1.
Simple Block Diagram
Speech
circuit
Audio
amplifier
Voice
switch
Dialer
Rev. 4570A–CORD–04/03
1
Pin Description
Pin
1
3
4
6
7
8
9
10
11
13
Symbol
DTMF
MIC 2
MIC 1
IND
V
L
GND
SENSE
V
B
SAO
V
MP
Function
Input for DTMF signals. Also used for the answering machine and hands-free input.
Non-inverting input of microphone amplifier
Inverting input of microphone amplifier
The internal equivalent inductance of the circuit is proportional to the value of the capacitor at this pin. A resistor
connected to ground may be used to reduce the DC line voltage.
Line voltage
Reference point for DC- and AC-output signals
A small resistor (fixed) connected from this pin to V
L
sets the slope of the DC characteristic and also affects the line-
length equalization characteristics and the line current at which the loudspeaker amplifier is switched on.
Unregulated supply voltage for peripheral circuits (voice switch); limited to typically 7 V
Output of loudspeaker amplifier
Regulated 3.3 V supply voltage for peripheral circuits. The maximum output current is 2 mA.
20
Control input for selection of line impedance
1) 600
W
IMPSEL 2) 900
W
3) Mute of second transmit stage (TXA); also used for indication of external supply (answering machine);
last chosen impedance is stored
TSACL
GSA
SA I
Time constant of anti-clipping of speaker amplifier
Current input for setting the gain of the speaker amplifier. Adjustment characteristic is logarithmical.
For RGSA > 2 MW, the speaker amplifier is switched off.
Speaker amplifier input (for loudspeaker, tone ringer and hands-free use)
Three-state input of transmit mute:
1) Speech condition; inputs MIC1/MIC2 active
2) DTMF condition; input DTMF active. A part of the input signal is passed to the receiving amplifier as a
confidence signal during dialing.
3) Input DTMF used for answering machine and hands-free use; receive branch is not affected.
Attenuation of acoustical feedback suppression. Maximum attenuation of the AFS circuit is set by a resistor at this
pin. Without the resistor, AFS is switched off.
Input of transmit level detector
Input of receive level detector
Time constant of transmit level detector
Time constant of receive level detector
Automatic gain adjustment with line current. A resistor connected from this pin to GND sets the starting point.
Max. gain change is 6 dB.
Internal reference current generation; RREF = 62 kW; IREF = 20 µA
Side tone reduction output. Output resistance is approximately 300
W.
Maximum load impedance is 10 kW.
Reference node for microphone, earphone and loudspeaker amplifier. Supply for electret microphone (IM
£
300 µA).
Input for side-tone network
Output of receiving amplifier
A resistor connected from this pin to GND sets the receiving amplification of the circuit; amplifier RA1 can be
muted by applying V
MP
to G
R
Time constant of anti-clipping in transmit path
Input of receiving path; input impedance is typically 80 kW
A resistor from this pin to GND sets the amplification of the microphone and DTMF signals; the input amplifier can
be muted by applying V
MP
to G
T
.
21
22
23
24
MUTX
25
26
27
28
29
30
31
32
33
36
39
40
41
42
44
ATAFS
INLDT
INLDR
TLDT
TLDR
AGA
IREF
STO
V
M
STI
RECO
G
R
TTXA
RECIN
G
T
4
U4089B-M
4570A–CORD–04/03
U4089B-M
DC Line Interface and
Supply-voltage
Generation
The DC line interface consists of an electronic inductance and an output stage which
charges the capacitor at V
B
. The value of the equivalent inductance is given by:
L = R
SENSE
´
C
IND
´
(R
DC
´
R
30
)/(R
DC
+ R
30
)
In order to improve the supply during worst-case operating conditions, the PNP current
source (I
BOPT
)
supplies an extra amount of current to the supply voltages when the NPN
in parallel is unable to conduct current.
The U4089B-M contains a series regulator which provides a supply voltage V
MP
of 3.3 V
at the 2 mA suitable for a microprocessor.
Figure 4.
DC Line Interface with Electronic Inductance and Generation of Regulated
and Unregulated Supply
V
L
10
W
R
SENSE
SENSE
I
BOPT
< 5 mA
C
IND
10 µF
IND
R
DC
+
-
R
30
30 kW
7V
V
OFFS
220 µF
+
-
3.3 V
V
MP
3.3 V/
2 mA
47 µF
V
B
5
4570A–CORD–04/03
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