Features
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Adjustable DC Characteristic
Transmit and Receive Gain Adjustable
Symmetrical Input of Microphone Amplifier
Anti-clipping in Transmit Direction
Automatic Line-loss Compensation
Built-in Ear Protection
DTMF and MUTE Input
Adjustable Sidetone Suppression Independent of Sending and Receiving Amplification
Integrated Amplifier for Open-listening 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
Filters Against EMI on Critical I/O
Monolithic
Integrated
Feature Phone
Circuit
U4089B-P
Benefits
•
Complete System Integration of Analog Signal Processing on One Chip
•
Very Few External Components
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Less Components for EMI protection
Applications
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Feature Phones
Answering Machines
Fax Machines
Speaker Phones
1. Description
The telephone circuit U4089B-P is a linear integrated circuit for use in feature phones,
answering machines and fax machines. It contains the speech circuit, sidetone
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 loudspeaker amplifier enables
open-listening
or
hands-free operation. With an anti-feedback function, acoustical feedback during
open
listening
can be reduced significantly. The generated supply voltage is suitable for a
wide range of peripheral circuits.
Electrostatic sensitive device.
Observe precautions for handling.
Rev. 4518C–CORD–10/05
Figure 1-1.
Simple Block Diagram
Speech
circuit
Audio
amplifier
Voice
switch
Dialer
Figure 1-2.
Block Diagram
GT
44
4
3
MIC
TXA
1
STO
32
V
L
7
IMPSEL AGA IND
600Ω
20
30
6
SENSE V
B
9
10
V
MP
13
MIC1
MIC2
900Ω
Power
supply
33
V
M
DTMF
41
Impedance
control
TX
ACL
8
GND
TTXA
27
INLDR
INLDT
TLDR
TLDT
ATAFS
26
29
28
25
AGA
control
Acoustical
feedback
suppression
control
Current
supply
31
I
REF
Transmit
mute
control
Supply
11
SAO
21
SACL
R-
attenuation
TSACL
23
SAI
22
24
39
40
36
42
GSA
MUTX
RECO
GR
STI
RECIN
2
U4089B-P
4518C–CORD–10/05
U4089B-P
2. Pin Configuration
Figure 2-1.
Pinning SSO44
RECIN
ATAFS
INLDR
INLDT
RECO
TTXA
IREF
AGA
STO
MUTX
24
TSACL 21
TLDR
TLDT
GR
STI
NC
VM
NC
NC
NC
GT
30
29
27
26
44
43
42
41
40
39
37
35
34
33
38
36
32
31
28
25
NC 12
VMP 13
NC 14
NC 15
NC 16
NC 17
NC 18
NC 19
IMPSEL 20
Table 2-1.
Pin
1
3
4
6
7
8
9
10
11
13
Pin Description
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 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 7V.
Output of loudspeaker amplifier.
Regulated supply voltage 3.3V for peripheral circuits. The maximum output current is 2 mA.
Control input for selection of line impedance
1) 600Ω
2) 900Ω
3) Mute of second transmit stage (TXA); also used for indication of external supply (answering machine);
last chosen impedance is stored.
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 MΩ, the speaker amplifier is switched off.
Speaker amplifier input (for loudspeaker, tone ringer and hands-free use).
20
IMPSEL
21
22
23
Note:
TSACL
GSA
SAI
Filters against electromagnetic interference (EMI) are located at pins MIC1, MIC2, RECIN and STI.
SENSE
DTMF
MIC2
MIC1
GND
GSA 22
SAO 11
NC
NC
IND
VB 10
1
2
3
4
5
6
7
8
VL
9
23
SAI
NC
3
4518C–CORD–10/05
Table 2-1.
Pin
Pin Description (Continued)
Symbol
Function
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 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. Maximum gain change is 6 dB.
Internal reference current generation; RREF = 62 kΩ; IREF = 20 µA
Side-tone reduction output. Output resistance is approximately 300Ω Maximum load impedance is 10 kΩ.
.
Reference node for microphone-earphone and loudspeaker amplifier. Supply for electret microphone
(IM
≥
300 mA).
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 kΩ.
A resistor from this pin to GND sets the amplification of microphone and DTMF signals; the input
amplifier can be muted by applying V
MP
to G
T
.
24
MUTX
25
26
27
28
29
30
31
32
33
36
39
40
41
42
44
Note:
ATAFS
INLDT
INLDR
TLDT
TLDR
AGA
IREF
STO
V
M
STI
RECO
G
R
TTXA
RECIN
G
T
Filters against electromagnetic interference (EMI) are located at pins MIC1, MIC2, RECIN and STI.
4
U4089B-P
4518C–CORD–10/05
U4089B-P
3. 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-P contains a series regulator which provides a supply voltage V
MP
of 3.3V at 2 mA
suitable for a microprocessor.
Figure 3-1.
DC Line Interface With Electronic Inductance and Generation of Regulated
and Unregulated Supply
10
R
SENSE
SENSE
I
BOPT
< 5 mA
C
IND
10
µF
+
IND
R
DC
-
R
30
30 kΩ
7V
V
OFFS
+
-
3.3V
V
MP
3.3V/
2 mA
V
L
47
µF
V
B
220
µF
Figure 3-2.
Functional Blocks for Power Supply
V
B
Power
supply
Voltage
regulator
7V
V
MP
V
L
ES
LIDET
V
LON
IMPED
CONTR
IMPSEL
TXA
TXACL
OFFSA
COMP
SAL, SA
SACL
AFS
MIC, DTMF
AGA, RA
TX MUTE
MUT REC, STBAL
RECATT
5
4518C–CORD–10/05
