U4084B [TEMIC]
Low-Voltage, Voice-Switched Circuit for Hands-Free Operation; 低电压，语音电路交换的免提操作
| 型号： | U4084B |
| 厂家： | 
TEMIC SEMICONDUCTORS |
| 描述： | Low-Voltage, Voice-Switched Circuit for Hands-Free Operation |
| 文件： | 总26页 (文件大小：544K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
U4084B
Low-Voltage, Voice-Switched Circuit for Hands-Free Operation
Description
The low-voltage, voice-switched speakerphone circuit disable, dial tone detector and mute function etc.
U4084B incorporates the features listed below. The ver- Due to low-voltage operation, it can be operated either by
satility of the device is further enhanced by giving access low supply voltage or via a telephone line requiring
to internal circuit points.
4.0 mA typ. Further features are stand-alone operation
The block diagram shows amplifiers, level detectors, via a coupling transformer (Tip and Ring) or in
transmit and receive attenuators operating in comple- conjunction with a handset speech network, as shown in
mentary functions, back ground noise monitors, chip figure 2.
Features
Benefits
Low-voltage operation: 3.0 to 6.5 V
Fast channel switching enables quasi duplex
Attenuator gain range between
transmit and receive: 52 dB
operation
Low current consumption for high output volume
Optimized U3800BM interface
Four-point signal sensing for improved sensitivity
Monitoring system for background-noise level
Microphone-amplifier gain adjustable
Mute function
Chip disable for active/ standby operation
Dial tone detector
Compatible with the speaker amplifier U4083B
Case: DIP24 or SO24
TELEFUNKEN Semiconductors
1 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Block Diagram
MIC
8
MICO TLI2
TI
TO
7
14
6
5
–
T attenuator
V
B
+
9
MUTE
V
S
24
CPR
AGC
13
Background-
noise monitor
Background-
noise monitor
CPT
20
22
22
TLI1
RLO1
TLO1
15
Level
detectors
Attenuator
control
Level
detectors
TLO2
RLO2
16
4
Dial tone
detector
V
S
+
–
1
3
GND
CD
V
B
400 Ω
R attenuator
U4084B
12
11
17
RLI2
19
18 10
RI VCI
23
RLI1
12626
V
C
RECO
B
T
Figure 1. Block diagram
2 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Figure 2. Block diagram with external circuit
TELEFUNKEN Semiconductors
3 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Pin Description
Pin Symbol
Function
Pin Symbol
Function
Response time.
An RC at this pin sets the response
time for the circuit to switch modes.
1
2
3
GND Ground
11
C
T
NC
CD
Not connected
Chip disable.
12
V
B
Output voltage ≈ V
.
S/2
A logic LOW (< 0.8 V) sets normal
operation. A logic HIGH (> 2.0 V)
disables the IC to conserve power.
The input impedance is nominally
90 k
It is a system AC ground, and biases
the volume control. A filter cap is
required.
13
CPT
An RC at this pin sets the time
constant for the transmit background
monitor.
4
V
S
Supply voltage 2.8 to 6.5 V,
approximately @ 4 mA.
The AGC circuit reduces the receive
attenuator gain @ 25 dB.
Receive mode @ 2.8 V.
14
15
TLI2 Transmit-level detector input on the
microphone/ speaker side.
TLO2 Transmit-level detector output on
the microphone/ speaker side, and
input to the transmit background
monitor.
5
6
TO
TI
Transmit attenuator output.
The DC level is approximately V .
B
Transmit attenuator input.
Max. signal level is 350 mV
The input impedance is approxi-
mately 10 k
.
16
17
18
RLO2 Receive-level detector output on the
microphone/ speaker side
rms
RLI2 Receive-level detector input on the
microphone/ speaker side
7
8
MICO Microphone amplifier output.
The gain is set by external resistors.
RI
Input receive attenuator and dial-
tone detector.
MIC
Microphone amplifier input.
The bias voltage is approximately
The max. input level is 350 mV
.
rms
V .
The input impedance is approxi-
mately 10 k
B
9
MUTE Mute input.
A logic LOW (< 0.8 V) sets normal
19
20
21
22
RECO Receive attenuator output.
DC level is approximately V .
operation. A logic HIGH (> 2.0 V)
mutes the microphone amplifier
without affecting the rest of the
circuit. The input impedance is
nominally 90 k
B
TLI1 Transmit-level detector input on the
line side
TLO1 Transmit-level detector output on
the line side
10
VCI
Volume control input.
When VCI = V , the receive attenu-
ator is at maximum gain in the
receive mode.
RLO1 Receive-level detector output on the
line side, and input to the receive
background monitor
B
When VCI = 0.3 V , the receive
gain is 35 dB lower. This does not
affect the transmit mode.
B
23
24
RLI1 Receive-level detector input on the
line side
CPR
An RC at this pin sets the time
constant for the receive background
monitor
4 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Absolute Maximum Ratings
Reference point Pin 1, T
= 25°C, unless otherwise specified.
amb
Parameters
Symbol
Value
–1.0 to +7.0
Unit
V
Supply voltage
Voltages
Pin 4
V
S
Pins 3 and 9
Pin 10
–1.0 to (V + 1.0)
S
–1.0 to (V + 0.5)
V
S
Pins 6 and 18
–0.5 to (V + 0.5)
S
Storage temperature range
Junction temperature
Ambient temperature range
Power dissipation
T
T
–55 to +150
125
–20 to +60
°C
°C
°C
stg
j
T
amb
T
amb
= 60°C
DIP24
SO24
P
P
650
520
mW
tot
tot
Maximum Thermal Resistance
Parameters
Symbol
Value
Unit
Junction ambient
DIP24
SO24
R
thJA
R
thJA
100
120
K/W
K/W
Operation Recommendation
Parameters
Supply voltage
CD input
Test Conditions / Pins
Symbol
Min.
3.5
0
Typ.
–
–
Max.
6.5
V
S
Unit
V
V
Pin 4
Pin3
V
S
MUTE input
Pin 9
Output current
Volume control input
Attenuator input signal
voltage
Microphone amplifier
Load current
Pin 12
Pin 10
Pins 6 and 18
I
–
–
–
–
500
A
V
mV
rms
B
VCI
0.3
V
B
V
B
0
0
0
0
350
–
–
–
40
dB
@ RECO, TO Pins 5, 19
2.0
1.0
+60
@ MICO
Pin 7
mA
Ambient temperature range
T
amb
–20
–
°C
TELEFUNKEN Semiconductors
5 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Electrical Characteristics
T
amb
= +25°C, V = 5.0 V, CD 0.8 V, unless otherwise specified
S
Parameters
Test Conditions / Pins
Symbol
Min.
50.0
Typ.
Max.
Unit
Power supply
Supply current
V = 6.5 V, CD = 0.8 V
V = 6.5 V, CD = 2.0 V
I
4.0
600.0
6.0
800.0
mA
A
S
S
S
CD input resistance
CD input voltage
V = V = 6.5 V
R
CD
90.0
k
S
CD
– High
– Low
V
CDH
2.0
0.0
V
S
V
V
CDL
0.8
Output voltage
V = 3.5 V
V = 5.0 V
S
V
B
1.3
2.1
V
S
1.8
2.4
Output resistance
I
= 1.0 mA
R
400.0
54.0
VB
OVB
Power supply rejection
ratio
C
= 220 F, f = 1.0 kHz
PSRR
dB
dB
VB
Attenuators
Receive attenuator gain
f = 1.0 kHz, V = V
CI B
R mode, RI = 150 mV
G
R
4.0
6.0
8.0
rms
(V = 5.0 V)
S
R mode, RI = 150 mV
rms
(V = 3.5 V)
S
Gain change
V = 3.5 V vs. V = 5.0 V
G
G
–0.5
0.0
+0.5
–15.0
–17.0
54.0
S
S
R1
AGC gain change
Idle mode
–V = 2.8 V vs. V = 5.0 V
–25.0
–20.0
52.0
S
S
R2
RI = 150 mV
G
RI
–22.0
49.0
27.0
dB
rms
Range R to T mode
Volume control range
RECO DC voltage
RECO DC voltage
RECO high voltage
G
R3
R mode, 0.3 V < V < V
V
CR
35.0
dB
V
B
CI
B
R mode
V
V
B
RECO
R to T mode
V
RECO
mV
V
10
150.0
I = 1.0 mA
O
V
3.7
RECOH
RI = V + 1.5 V
B
RECO low voltage
I = 1.0 mA
V
–1.5
10.0
–1.0
14.0
V
k
O
RECOL
RI = V –1.0 V,
B
output measured w.r.t. V
B
RI input resistance
RI < 350 mV
R
RI
7.0
rms
Transmit attenuator gain
f = 1.0 kHz
T mode, TI = 150 mV
Idle mode, TI = 150 mV
Range T to R mode
G
4.0
–22.0
49.0
6.0
–20.0
52.0
8.0
–17.0
54.0
rms
T
G
TI
G
TI
dB
rms
TO DC voltage
TO DC voltage
TO high voltage
T mode
V
TO
V
TO
V
V
B
T to R mode
mV
100
150.0
I
= –1.0 mA
O
TI = V + 1.5 V
V
3.7
7.0
V
V
B
TOH
TO low voltage
I = +1.0 mA
V
–1.5
–1.0
14.0
O
TOL
TI = V – 1.0 V,
B
output measured w.r.t. V
B
TI input resistance
Gain tracking
TI < 350 mV
R
10.0
0.5
k
rms
TI
G
R + G
T, @ T, Idle, R
G
dB
TR
6 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Parameters
Test Conditions / Pins
Pin 14 – V
Symbol
Min.
Typ.
Max.
Unit
Attenuator control
C voltage
V
CT
T
B
R mode, V = V
Idle mode
T mode
240.0
0.0
–240.0
CI
B
mV
C source current
R mode
T mode
I
–85.0
40.0
–60.0
60.0
0.0
–40.0
85.0
A
A
T
CTR
C sink current
T
I
CTT
C slow idle current
T
I
A
CTS
C fast idle internal
resistance
R
1.5
2.0
3.6
20.0
k
T
FI
VCI input current
I
–60.0
15.0
nA
VCI
Dial tone detector
threshold
V
DT
10.0
mV
Microphone amplifier V
< 0.8 V, G
= 31 dB
MUTE
VCL
Output offset
V
V ,
MICO
vos
–50.0
70.0
0.0
+50.0
mV
MICO –
B
Feedback R = 180 k
Open loop gain
f < 100 Hz
G
VOLM
80.0
1.0
dB
MHz
V
Gain bandwidth
GBW
M
Output high voltage
Output low voltage
Input bias current (MIC)
Muting ( gain)
I = –1.0 mA, V = 5.0 V
O
V
MICOH
3.7
S
I = +1.0 mA
O
V
MICOL
200.0
mV
nA
I
–40.0
BM
G
f = 1.0 kHz, V
300 Hz < f < 10 kHz
= 2.0 V
–55.0
dB
dB
MUTE
G
–68.0
90.0
MUTE input resistance
MUTE input high
MUTE input low
Distortion
V
V
= 6.5 V
R
MUTE
50.0
2.0
k
S = MUTE
V
MUTEH
V
S
V
V
%
V
MUTEL
0.0
0.8
300 Hz < f < 10 kHz
THD
0.15
1.0
M
Level detectors and background-noise monitors
Transmit receive switching Ratio of current
I
0.8
1.2
TH
threshold
at RLI1 + RLI2 to 20 A
at TLI1 + TLI2 to switch
from T to R
Source current
Sink current
at RLO1, RLO2, TLO1,
TLO2
I
I
–2.0
4.0
mA
A
LSO
LSK
at RLO1, RLO2, TLO1,
TLO2
CPR, CPT output
resistance
I = 1.2 mA
R
150
–0.2
O
CP
CPR, CPT leakage current
System distortion
R mode
I
A
CPLK
From RI to RECO
d
d
0.5
0.8
3.0
3.0
%
%
R
T mode
From MIC to TO includes
T attenuator
T
TELEFUNKEN Semiconductors
7 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Temperature Characteristics
Parameter
Typical Value @ 25°C
4.0 mA
Typical Change –20 to +60°C
–0.3%/°C
Supply current, CD = 0.8 V
Supply current, CD = 2.0 V
I
I
S
400.0 A
2.1 V
–0.4%/°C
S
V output voltage, V = 5.0 V
V
O
+0.8%/°C
B
S
Attenuator gain (max. gain)
+6.0 dB
–46.0 dB
10.0 k
0.0008 dB/°C
0.004 dB/°C
+0.6%/°C
Attenuator gain (max. attenuation)
Attenuator input resistance (@ TI, RI)
Dial-tone detector threshold
15.0 mV
60.0 A
0.0 mV
+20.0 V/°C
0.15%/°C
CT source, sink current
Microphone, hybrid offset
4.0 V/°C
0.02%/°C
10.0 nA/°C
Transmit receive switching threshold
Sink current at RLO1, RLO2, TLO1, TLO2
1.0
4.0 A
8 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Introduction
General
Transmit and Receive Attenuators
TI, TO and RI, RECO
The fundamental difference between the operation of a
speakerphone and a handset is that of half-duplex versus
full-duplex. The handset is full-duplex since conversation
can occur in both directions (transmit and receive) simul-
taneously. A speakerphone has higher gain levels in both
paths, and attempting to converse full-duplex results in
oscillatory problems due to the loop that exists within the
system. The loop is formed by the receive and transmit
paths, the hybrid and the acoustic coupling (speaker to
microphone).
The attenuators are operating complementary, i.e., when
one is at maximum gain (+6.0 dB), the other is at maxi-
mum attenuation (–46 dB), and vice versa, i.e., both are
never completely on or off. The sum of their gains re-
mains constant (within a nominal error band of 0.5 dB)
at a typical value of –40 dB (see figure 8). The attenuators
control the transmit and receive paths to provide the half-
duplex operation required in a speakerphone.
The attenuators are non-inverting, and have a –3.0 dB
(from max. gain) frequency of approximately 100 kHz.
The input impedance of each attenuator (TI and RI) is
nominally 10 k (see figure 3). To prevent distortion the
Today, the only practical and economical solution is to de-
sign the speakerphone in half-duplex mode, i.e., only one
person speaks at a time, while the other listens. To achieve
this, a circuit able to detect who is talking, to switch-on
the appropriate path (transmit or receive) and to switch-
off (attenuate) the other path is necessary. In this way, the
loop gain is maintained less than unity. The circuit has to
detect quickly a change from one speaker to the other and
to switch the circuit accordingly. Due to its speech-level
detectors, the circuit operates in a “hands-free” mode,
eliminating the need for a “push-to-talk” switch.
input signal should be limited to 350 mV . The maxi-
rms
mum recommended input signal is independent from the
volume control setting. The diode clamp on the inputs
limits the input swing, and therefore the maximum nega-
tive output swing. The output impedance is less than 10
until the output current limit (typically 2.5 mA) is
reached.
12627
V
11 kΩ
B
The handset has the same loop as the speakerphone.
Oscillations do not occur because the gains are consider-
ably lower, and there is almost no coupling from the
earpiece to the mouthpiece (the receiver is normally held
at a person’s ear).
5 kΩ
95 kΩ
RI 18
TI 6
C
T
11
The U4084B provides the level detectors, attenuators,
and switching control necessary for proper operation of
the speakerphone. The detection sensitivity and timing
are externally controllable. Additionally, the U4084B
provides background-noise monitors which make the
circuit insensitive to room and line noise, hybrid
amplifiers for interfacing to tip and ring, the microphone
amplifier, and other associated functions.
Figure 3. Attenuator input stage
The attenuators are controlled by the signal output of the
control block which is measurable at the C pin (Pin 11).
T
When the C pin is at +240 mV w.r.t. V , the circuit is in
T
B
receive mode (the receive attenuator is at 6.0 dB). When
the C pin is at –240 mV w.r.t. V , the circuit is in transmit
T
B
mode (the transmit attenuator is at 6.0 dB). The circuit is
in idle mode when the C voltage is equal to V causing
T
B
the attenuators’ gain to be half-way between their ful-
ly-on and fully-off position (–20 dB each). Monitoring
the C voltage (w.r.t. V ) is the most direct method of
T
B
monitoring the circuit’s mode.
The attenuator control has seven inputs: two from the
comparators operated by the level detectors, two from the
background noise monitors, volume control, dial-tone
detector, and AGC. They are described as follows:
TELEFUNKEN Semiconductors
9 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
rator goes to the attenuator control block. Likewise,
outputs RLO2 and TLO2 feed a second comparator which
also goes to the attenuator control block. The truth table
for the effects of the level detectors is given in the section
“Attenuator Control Block.
Level Detectors, Figure 4
There are four level detectors, two on the receive side and
two on the transmit side. As shown in figure 4, the terms
in parentheses form one system, and the other terms form
the second system. Each level detector is a high-gain
amplifier with back-to-back diodes in the feedback path,
resulting in a non-linear gain which permits operation
over a wide dynamic range of speech levels. Refer to
figures 9, 10 and 11 for their AC and DC transfer charac-
teristics. The sensitivity of each level detector is
determined by the external resistor and capacitor at each
input (TLI1, TLI2, RLI1, and RLI2). Each output charges
an external capacitor through a diode and limiting
resistor, thus providing a DC representation of the input
AC signal level. The outputs have a quick rise time (deter-
mined by the capacitor and an internal 350- resistor),
and a slow decay time set by an internal current source
and the capacitor. The capacitors on the four outputs
should have the same value ( 10%) to prevent timing
problems.
Background-Noise Monitors
The background-noise monitiors distinguish speech
(which consists of bursts) from background noise (a rela-
tively constant signal level). There are two
background-noise monitors – one for the receive path and
the other for the transmit path. Referring to figure 4, the
receive background-noise monitor is operated by the
TLI2–TLO2 level detector.
Background-noise monitoring is carried out by storing a
DC voltage representative of the respective noise levels
in capacitors at CPR and CPT. The voltages at these pins
have slow rise times (determined by the external RC), but
fast decay times. If the signal at RLI1 (or TLI2) changes
slowly, the voltage at CPR (or CPT) will remain being
On the receive side, one level detector (RLI1) is at the more positive than the voltage at the non-inverting input
receive input receiving the same signal as at tip and ring, of the monitor’s output comparator. When speech is
and the other (RLI2) is at the output of the speaker ampli- present, the voltage on the non-inverting input of the
fier (see figure 2). On the transmit side, one level detector comparator will rise quicker than the voltage at the
(TLI2) is at the output of the microphone amplifier while inverting input (due to the burst characteristic of speech),
the other (TLI1) is at the hybrid output. Outputs RLO1 causing its output to change. This output is sensed by the
and TLO1 feed a comparator. The output of this compa- attenuator control block”.
VS
Level detector
Background-noise monitor
100kΩ
24
4µA
(13)
CPR
(CPT)
23
–
–
RLI1 (14)
(TLI2)
–
+
–
+
+
350Ω
47µF
VB
+
22 (15)
5.1kΩ
RLO1
(TLO2)
56kΩ
36 mV
0.1µF
33kΩ
2µF
12
VB
Signal
input
Level detector
C4 (C3)
4µA
VB
–
C2 (C1)
+
+
20
–
350Ω
2µF
to
Comparator
(17)
TLI1
(RLI2)
21 (16)
attenuator
control
block
TLO1
(RLO2)
5.1kΩ
0.1µF
12673
Signal input
Figure 4. Level detectors
10 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
The 36-mV offset at the comparator’s input keeps the
comparator from changing state unless the speech level
exceeds the background noise by approximately 4.0 dB.
The time constant of the external RC (approximately
4.5 s) determines the response time to background-noise
variations.
to R attenuator
RI
18
to attenuator
control
C4
Volume Control
V
B
12674
The volume control input at VCI (Pin 10) is sensed as a
voltage w.r.t. V . It affects the attenuators only in receive
mode and has no effect in the idle or transmit modes.
B
Figure 5. Dial-tone detector
AGC
In receive mode, the receive attenuator gain, G , is
R
6.0 dB, and the transmit attenuator gain, G , is –46 dB
The AGC circuit affects the circuit only in receive mode,
T
under the condition that VCI = V . When VCI < V , the
and only when the supply voltage is less than 3.5 V. As V
B
B
S
receive attenuator gain is reduced (figure 10), whereas the
transmit attenuator gain is increased. Their sum,
however, remains constant. A voltage deviation at VCI
< 3.5 V, the gain of the receive attenuator is reduced (see
figure 13). The transmit path attenuation changes such
that the sum of the transmit and receive gains remains
constant.
changes the voltage at C , which in turn controls the
T
attenuators (see “Attenuator Control Block”).
The purpose of this feature is to reduce the power (and the
current) used by the speaker when a line-powered
speakerphone is connected to a long line where the
available power is limited. By reducing the speaker
The volume control setting does not affect the maximum
attenuator input signal at which noticeable distortion
occurs.
power, the voltage sag at V is controlled, preventing
S
possible erratic operation.
The bias current at VCI is typically –60 nA. It does not
vary significantly with the VCI voltage or supply voltage
V .
S
Attenuator Control Block
The attenuator control block has seven inputs:
Dial-Tone Detector
The output of the comparator operated by RLO2 and
TLO2 (microphone/speaker side) – designated C1
The dial-tone detector is a comparator with one side
connected to the receive input (RI) and the other to V
with a 15-mV offset (see figure 5). If the circuit is in idle
mode, and the incoming signal is greater than 15 mV (10
B
The output of the comparator operated by RLO1 and
TLO1 (Tip/Ring side) – designated C2
The output of the transmit background-noise monitor
– designated C3
mV ), the comparator’s output will change, disabling
rms
the receive idle mode. The receive attenuator will then be
at a setting determined mainly by the volume control.
The output of the receive background-noise monitor
– designated C4
This circuit prevents the dial tone (which would be
considered as continuous noise) from fading away as the
circuit would have the tendency to switch to the idle
mode. By disabling receive idle mode, the dial tone
remains at the normally expected full level.
The volume control
The dial-tone detector
The AGC circuit
TELEFUNKEN Semiconductors
11 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
The single output of the control block controls the two
attenuators. The effect of C1–C4 is as follows:
b) the transmit background-noise monitor indicates
the presence of speech
2. The circuit will switch to receive mode if:
Inputs
Output
Mode
C1
T
C2
T
C3
1
C4
X
Y
Y
1
a) both receive level detectors sense higher signal
levels relative to the respective transmit level
detectors, and
Transmit
Fast idle
Fast idle
Receive
Slow idle
Slow idle
Slow idle
Slow idle
T
R
T
Y
Y
X
0
R
R
T
b) the receive background-noise monitor indicates
the presence of speech
R
T
X
0
3. The circuit will switch to fast idle mode if the level
detectors disagree on the relative strengths of the
signal levels, and at least one of the background-
noise monitors indicates speech. If, e.g., there is a
signal at the microphone amp output (TLI2) to over-
ride the speaker signal (RLI2) and there is sufficient
signal at the receive input (RLI1) to override the
signal at the hybrid output (TLI1), and either one or
both background monitors indicate speech, then the
circuit switches to fast idle mode.
T
R
T
0
R
R
0
0
R
X
0
X = don’t care; Y = C3 and C4 are not both 0.
Terms Definition
11. “Transmit” means the transmit attenuator is fully on
(+ 6.0 dB), and the receive attenuator is at max. atten-
uation (– 46 dB).
Undesired switching to idle mode may occur if one
of the following conditions is met:
12. “Receive” means both attenuators are controlled by
the volume control. At max. volume, the receive
attenuator is fully on (+ 6.0 dB), and the transmit
attenuator is at max. attenuation (– 46 dB).
a) when both persons speaking try to talk at the
same time, and
b) when one of the persons speaking is in a very
noisy environment, forcing the other one to con-
tinually override that noise level.
13. “Fast Idle” means both transmit and receive speech
are present in approximately equal levels. The
attenuators are quickly switched (30 ms) to idle until
one speech level dominates the other.
In general, fast idle mode occurs rarely.
4. The circuit will switch to slow idle mode when
14. “Slow Idle” means speech has ceased in both transmit
and receive paths. The attenuators are then slowly
switched (1 s) to idle mode.
a) both persons at the phone are quiet (no speech
present), or
15. Switching to the full transmit of receive modes from
any other mode is at the fast rate ( 30 ms).
b) when the speech levelof one of the persons
talking is continuously overriden by noise at the
other speaker’s location.
Summary
The time required to switch the circuit between
transmit, receive, fast idle and slow idle mode is
deter-mined in part by the components at Pin 11,
(see the section “Switching Times” for a more
1. The circuit will switch to transmit mode if:
a) both transmit level detectors sense higher signal
levels relative to the respective receive level
detectors (TLI1 versus RLI1, TLI2 versus RLI2),
and
detailed explanation). A schematic of the C
circuitry is shown in figure 6.
T
12 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
V
R
B
12
11
–
to attenuators
T
+
2kΩ
C
T
I
1
4
Attenuator
control
C
C1 ... C4
T
I
2
Volume control
Dial-tone detector
AGC
60µA
12675
Figure 6. CT attenuator control block circuit
Operation of the CT Circuitry
Microphone Amplifier, Pins 7, 8 and 9
The non-inverting input of the microphone amplifier
–
R is typ. 120 k and C is typ. 5.0 F.
T T
(Pins 7 and 8) is connected to V , while the inverting in-
B
–
To switch to receive mode, I is turned on (I is
1
2
put and the output are pinned out.
off), charging the external capacitor to + 240 mV
Unlike most op amps, the amplifier has an all NPN output
stage which maximizes phase margin and gain band-
width. This feature ensures stability at gains less than
unity, as well with a wide range of reactive loads.
above V (An internal clamp prevents further
B.
charging of the capacitor).
–
–
To switch to transmit mode, I is turned on (I is
2
1
off) bringing down the voltage on the capacitor
The open loop gain is typically 80 dB (f < 100 Hz), and
the gain-bandwidth is typ. 1.0 MHz (see figure 4). The
to – 240 mV with respect to V .
B
maximum p-p output swing is typ. (V – 1 V) with an out-
S
To switch to idle mode quickly (fast idle), the
current sources are turned off, and the internal
2.0-k resistor is switched on, discharging the
put impedance of < 10 until current limiting is reached
(typ. 1.5 mA). The input bias current at MIC is typically
– 40 nA.
capacitor to V with a time constant = 2.0 k
B
C .
T
–
To switch to idle slowly (slow idle), the current
sources are turned off, the switch at the 2.0-k
resistor is open, and the capacitor discharges to
V
R
S
MF
7
+
–
V
R
B
MI
8
9
V with a time constant = R
C .
T
B
T
MICO
MIC
from
Mike
V
S
90kΩ
MUTE
75kΩ
12676
Figure 7. Microphone amplifier and mute
TELEFUNKEN Semiconductors
13 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
When activated, the muting function (Pin 9) reduces the
gain of the amplifier to approximately – 39 dB (with RMI
= 5.1 k ) by shorting the output to the inverting input (see
10
0
figure 7). The mute input has
a threshold of
approximately 1.5 V, and the voltage at this pin must be
– 10
– 20
– 30
– 40
– 50
kept within the range of ground and V (see figure 15). If
R attenuator
S
T attenuator
the mute function is not used, the pin should be grounded.
Power Supply, VB, and Chip Disable
The power supply voltage at Pin 4 (V ) is between 3.5 and
S
6.5 V for normal operation. Reduced operation at 2.8 V
is, however, also possible (see figure 13 and the AGC
section). The power supply current is shown in figure 16
for both operations, power-up and power-down mode.
– 320
– 160
0
160
320
V
– V (mV)
CT
B
93 7767 e
The output voltage at V (Pin 12) is approximately
B
(V –0.7)/2. and provides the AC ground for the system.
Figure 8. Attenuator gain versus VCT (Pin 11)
S
The output impedance at V is approximately 400 (see
B
figure 17), and forms together with the external capaci-
500
tor at V
a low-pass filter for power supply rejection.
B
Figure 18 indicates the amount of rejection for different
capacitors. The capacitor values depend on whether the
circuit is powered by the telephone line or a power supply.
400
300
200
100
0
Since V biases the microphone amplifier, the amount of
B
supply rejection at its output is directly related to the
rejection at V , as well as its gain. Figure 19 depicts this
B
graphically.
The chip disable (Pin 3) permits powering down the IC to
conserve power and/or for muting purposes. With CD
< 0.8 V, normal operation is in effect.
0
– 20
– 40
– 60
– 80
– 100
With CD > 2.0 V and < V , the IC is powered down. In
I ( A)
S
I
93 7768 e
the power-down mode, the microphone amplifier is
disabled, and its output goes to a high impedance state.
Additionally, the bias is removed from the level detectors.
Figure 9. Level-detector DC transfer characteristics
300
The bias is not removed from the attenuators (Pins 5, 6,
18 and 19), or from Pins 10, 11 and 12 (the attenuators are
disabled, however, and will not pass a signal). The input
impedance at CD is typically 90 k and has a threshold
of approximately 1.5 V. The voltage at this pin must be
R = 5.1 k
C = 0.1
F
250
↓
←
R = 10 k
200
150
100
C = 0.047 F or 0.1
F
kept within the range of ground and V (see figure 15). If
S
CD is not used, the pin should be grounded.
f = 1 kHz
50
0
4
60
80
100
0
20
V (mVrms)
i
93 7769 e
Figure 10. Level-detector AC transfer characteristics
14 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
10
0
20
10
0
v = 10 mV
– 10
– 20
– 30
– 40
i
– 10
v = 40 mV
i
– 20
– 30
– 40
100
1000
f (Hz)
10000
3.6
2.8
3
3.2
V (V)
3.4
93 7772 e
S
93 7770 e
Figure 11. Level-detector AC transfer characteristics
versus frequency
Figure 13. Receive attenuation gain versus VS
10
120
100
80
120
0
100
80
– 10
60
60
– 20
Receive mode
40
40
Gain
– 30
20
0
20
0
← Minimum recommended level
– 40
1000
0.1
0.3
0.5
VCI/V
0.7
0.9
1.2
0
1
10
100
94 7871 e
93 7771 e
f (kHz)
B
Figure 12. Receive attenuator versus volume control
Figure 14. Microphone amplifier open loop gain and phase
versus frequency
TELEFUNKEN Semiconductors
15 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
120
100
3.0
2.5
2.0
1.5
1.0
0.5
0
V
= 6 V
S
←Valid for 0 CD, MUTE
V →
S
80
60
40
20
0
V
= 3.5 V
S
8
2
4
6 6.5
0
0
0.5
1.0
1.5
2.0
2.5
93 7774 e
93 7776 e
Input Voltage (V)
–I (mA) (Load Current)
B
Figure 15. Input characteristics @ CD, MUTE
6
Figure 17. VB output characteristics
80
60
C
VB
= 1000
F
500
200
100
50
F
F
F
F
4
CD 0.8V
2
40
20
2V CD
V
S
0
8
0
2
4
6
2
0.3
1
3
f (kHz)
93 7778 e
94 7880 e
V ( V )
S
Figure 16. Supply current versus supply voltage
Figure 18. VB power-supply rejection versus frequency
characteristics and VB capacitor
16 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Design Hints
of the level detectors’ outputs to new speech is quick by
comparison (approximately 1.0 ms), determined by the
Switching Time, Figure 6
The switching time of the U4084B circuit is determined
internal 350
resistor and the external capacitor
by C (Pin 11, refer to figure 6), and the capacitors at the
(typically 2.0 F). The output’s decay time is determined
by the external capacitor, and an internal 4.0- A current
source giving a decay rate of 60 ms for a 120 mV
excursion at RLO or TLO. The total response time of the
circuit is not constant as it depends on the relative strength
of the signals at the different level detectors and the
timing of the signals with respect to each other. The
capacitors at the four outputs (RLO1, RLO2, TLO1,
TLO2) must have equal values ( 10%) to prevent
problems in timing and level response.
T
level-detector outputs (RLO1, RLO2, TLO1, TLO2), see
figure 2.
The switching time from idle to receive or transmit mode
is determined by the capacitor at C , together with the
T
internal current sources. The switching time is:
V
CT
5
T
I
240
20.0 ms
60
The rise time of the level detector’s outputs is too short
to be of significant. The decay time, however provides a
significant part of the “hold time” necessary to hold the
circuit during the normal pauses in speech.
where:
V
T
=
=
=
240 mV
5 F
60 A
C
I
The components at the inputs of the level detectors (RLI1,
RLI2, TLI1, TLI2) do not affect the switching time but
rather affect the relative signal levels required to switch
the circuit and the frequency response of the detectors.
If the circuit switches directly from receive to transmit
mode (or vice-versa), the total switching time is 40 ms.
The switching time depends on the mode selection. If the
circuit is switching to “fast idle”, the time constant is Design Equations
determined by the C capacitor, and the internal 2.0-k
T
Following definitions are used @ 1.0 kHz with reference
to figures 2 and 21 whereas coupling capacitors are
omitted for the sake of simplicity:
resistor. With C = 5.0 F, the time constant is
T
approximately 10 ms, resulting in a switching time of
approximately 30 ms (for 95% change). Fast idle is mode
may occur if both persons are talking at the same time,
thus trying to get control of the circuit. The switching
time from idle back to either transmit or receive mode is
described above.
–
G
MA
is the gain of the microphone amplifier
measured from the microphone output to TI
(typically 35 V/V, or 31 dB);
–
–
G
is the gain of the transmit attenuator,
T
By switching to “slow idle”, the time constant is
measured from TI to TO;
determined by the C capacitor and R , the external
T
T
G
EXT
is the gain of an external transmit amplifier
resistor (see figure 6). With C = 5.0 F, and R = 120 k ,
T
T
(typically 10.2 V/V, or 20.1 dB)
the time constant is approximately 600 ms, resulting a
switching time of approximately 1.8 seconds (for 95%
change). The switching to slow idle starts when both
speakers have stopped talking. The switching time back
to the original mode depends on how fast that person
starts talking again. The sooner the speaking starts during
the 1.8-second period, the faster the switching time since
a smaller voltage excursion is required. The switching
time is determined by the internal current source as
described above.
–
–
–
G
G
is the side-tone gain;
ST
is the gain of an external receive amplifier;
EXR
G is the gain of the receive attenuator measured
R
from RI to RECO;
–
–
G
is the gain of the speaker amplifier, mea-
SA
sured from RECO to the differential output of the
speaker amplifier (typically 22 V/V or 26.8 dB);
The above switching times occur after the level detectors
have detected the appropriate signal levels, since their
outputs operate the attenuator control block. The rise time
G
AC
is the acoustic coupling, measured from the
speaker differential voltage to the microphone
output voltage.
TELEFUNKEN Semiconductors
17 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
6
5
60
40
20
MICO
MICO,
4
3
2
C
VB
= 1000
F
TO,RO
TO
RO
= 220
F
1
0
0
0
10
1
3
4
5
6
94 7870 e
94 7872 e
f (kHz)
V
(V)
S
Figure 19. Power supply rejection of the microphone amplifier
Figure 20. Typical output swing versus VS
MIC amp.
MICO
ext. Transmit. amp.
TI
TO
12677
T attenuator
I1
R1
R2
I2
TLI1
–
–
Comparator
C1
Comparator
C2
Tip
+
+
Acoustic
coupling
Attenuator
control
GST
Hybrid
+
–
+
–
Ring
RLI2
I3
RLI1
I4
R3
R4
R attenuator
SAO
RECO
RI
Speaker amp.
ext. Receive amp.
Figure 21. Basic block diagram for design purposes
18 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
I) Loop Gain
The total loop gain (of figure 21) must add up to a value
< 0 dB to obtain a stable circuit. This can be expressed as:
VM
R2
GEXT
2
I2
GMA
GT
. . . . . . 7
GMA + GT + GEXT + GST + GEXR + GR + GSA + GAC < 0
. . . . . . 1
Since G
is the differential gain of the external transmit
EXT
amplifiers, it is divided by two to obtain the voltage V
2
applied to R . Comparator C2 switches when I = I . I is
defined by:
2
4
2
4
Using the typical numbers mentioned above, and using
the equation G + G = –40dB, the required acoustic cou-
T
R
VL
R4
pling can be determined:
I4
[GEXR
]
. . . . . . 8
G
AC
<–[31 + 20.1 + (–15) + 0 + (–40) + 26.8] + –22.9
Setting I = I , and combining the above equations results
in:
4
2
. . . . . . 2
An acoustic loss of at least 23 dB is necessary to prevent
instability and oscillations, commonly referred to as
“singing”. However, the following equations show that
greater values of acoustic loss are necessary to obtain
proper level detection and switching.
R4
R2
[GMA
GT
GEXR
GEXT
]
VL
VM
. . . 9
2
This equation defines the line voltage at Tip/Ring neces-
sary to switch comparator C2 in the presence of a
microphone voltage. The highest V occurs when the
L
II) Switching Thresholds
circuit is in transmit mode (G = + 6.0 dB). Using the
T
typical values for equation 9 yields:
To switch comparator C1, the currents I and I have to
1
3
be determined. When a receive signal V is applied to
L
V = 840 V (or V = 0.0019 V ) . . . . . . 10
L
M
M
L
Tip/Ring, a current I flows through R3 into RLI2 (see
3
At idle mode, where the gain of the two attenuators is –20
dB (0.1 V/V), equations 6 and 10 yield the same result:
figure 21) according to the following equation:
VL
R3
GSA
2
V
= 0.024 V . . . . . . 11
L
M
I3
GEXR
GR
. . . . . . 3
Equations 6, 10, and 11 define the thresholds for switch-
ing, and are represented in figure 22.
where the terms in the brackets are in V/V gain terms. The
speaker amplifier gain is divided by two since G is the
differential gain of the amplifier, and V is obtained from
one side of that output. The current I , coming from the
microphone circuit, is defined by:
SA
The “M” terms are the slopes of the lines (0.52, 0.024, and
0.0019) which are the coefficients of the three equations.
The M line represents the receive to transmit threshold
in that it defines the microphone signal level necessary to
switch to transmit in the presence of a given receive signal
level. The M line represents the transmit to receive
3
1
R
VM
GMA
I1
. . . . . . 4
T
R
1
threshold. The M line represents the idle condition, and
I
defines the threshold level on one side (transmit or
receive) necessary to overcome noise on the other.
where V is the microphone voltage. Since the switching
M
threshold occurs when I = I , combining the above two
1
3
equations yields:
MR
R1
R3
[GEXR
GR
GMA
GSA]
VM
VL
. . . 5
VM
2
MI
This is the general equation defining the microphone volt-
age necessary to switch comparator C1 when a receive
signal V is present. The highest V occurs when the
L
M
receive attenuator is at maximum gain (+ 6.0 dB). Using
the typical values of equation 5 results in:
MT
V
M
= 0.52 V
. . . . . . 6
L
To switch comparator C2, the currents I and I need to
2
4
be determined. When sound is applied to the microphone,
VL
12678
a voltage V is created by the microphone, resulting in
M
a current I into TLI1:
Figure 22. Switching thresholds
2
TELEFUNKEN Semiconductors
19 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Some comments on the graph (figure 22):
threshold can be reduced by connecting a resistor from RI
to ground. The resistor value is calculated from:
Acousting coupling and side-tone coupling were not
included in equations 6 and 11. Those couplings will
affect the actual performance of the final speaker-
phone due to their interaction with speech at the
microphone, and the receive signal coming in at Tip/
Ring. The effects of those couplings are difficult to
predict due to their associated phase shifts and fre-
quency response. In some cases, the coupling signal
will add, and other times substract from the incoming
signal. The physical design of the speakerphone en-
closure, as well as the specific phone line to which it
is connected, will affect the acoustic and side-tone
couplings, respectively.
VB
V
R
10 k
– 1
where V is the voltage at Pin 12, and V the amount of
threshold reduction. By connecting a resistor from V to
RI, the threshold can be increased. The resistor value is
calculated from:
B
S
VS–V
R
10 k
B – 1
V
where V is the amount of the threshold increase.
Background-Noise Monitors
For testing or circuit analysis purposes, the transmit or
receive attenuators can be set to the “on” position by
disabling the background noise monitors, and applying a
signal so as activate the level detectors. Grounding the
CPR pin will disable the receive background-noise
monitor, thereby indicating the “presence of speech” to
the attenuator control block. Grounding CPT does the
same for the transmit part.
The M line helps define the maximum acoustic
coupling permissible in a system, which can be found
from the following equation:
R
R1
GAC(MAX(
. . . . . 12
2
R3 GMA
Equation 12 is independent of the volume control setting.
Conversely, the acoustic coupling of a designed system
helps determine the minimum slope of that line. Using the
component values of figure 2 in equation 12 yields a
Additionally, the receive background-noise monitor is
automatically disabled by the dial-tone detector when-
ever the receive signal exceeds the detector’s threshold.
G
of –37 dB. Experience has shown, however,
AC(MAX)
that an acoustic coupling loss of >40 dB is desirable.
Transmit/Receive Detection Priority
The M line helps define the maximum sidetone cou-
T
pling (G ) permissible in the system, which can be
ST
Although the U4084B was designed to have an idle mode
such that the attenuators are halfway between their full-on
and full-off positions, the idle mode can be biased towards
the transmit or the receive side. By doing so, gaining
control of the circuit from idle will be easier for that side
towards which it is biased since that path will have less
attenuation at idle.
found from the following equation:
R1
R2
GST
. . . . . 13
2
Using the component values of figure 2 in equation 13
yields a maximum side-tone of 0 dB. Experience has
shown, however, that a minimum of 6.0-dB loss is prefer-
able.
By connecting a resistor from C (Pin 11) to ground, the
T
circuit will be biased towards the transmit side. The resis-
tor value is calculated from:
The above equations can be used to determine the resistor
values for the level detector inputs. Equation 5 can be
used to determine the R , 3 ratio and equation 9 can be
VB
V
1
R
RT
– 1
used to determine the R –R ratio. In figure 21, R –R
1
2
1
4
each represent the combined impedance of the resistor
and coupling capacitor at each level detector input. The
magnitude of each RC’s impedance should be kept within
the range of 2.0 to 15 k in the voiceband (due to the typi-
cal signal levels present) to obtain the best performance
from the level detectors. The specific R and C at each
location will determine the frequency response of that
level detector.
where:
R = 120 k (typ.) connected between Pin 11 and 12.
T
V = V – V11 (see figure 8).
B
By connecting a resistor from C (Pin 11) to V , the cir-
cuit will be biased towards the receive side. The resistor
value is calculated from:
T
S
VS – VB
R
RT
– 1
V
Application Information
The switching time will be somewhat affected in each
case due to the different voltage excursions required to get
Dial-Tone Detector
The threshold for the dial-tone detector is internally set at to transmit and receive from idle. For practical consider-
15 mV (10 mV ) below V (see figure 5). That ations, the V shift should not exceed 100 mV.
rms
B
20 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Applications
TELEFUNKEN Semiconductors
21 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
22 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
TELEFUNKEN Semiconductors
23 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
0.05µF
36kΩ
0.05µF
6.2kΩ
0.1µF
5.1kΩ
0.1µF
5.1kΩ
2µF
300kΩ
300kΩ
15µF
15µF
2µF
0.1µF 0.1µF
2µF
2µF
24
23
22
21
20
19
18
17
16
15
14
13
U4084B
1
2
3
5
6
4
7
8
9
10
11
12
220µF
0.1µF
120kΩ
620Ω
20µF
5µF
220pF
0.1µF
180kΩ
1.5MΩ
1kΩ
0.2µF
5.1kΩ
0.02µF
12682
24 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Package Information
Package DIP24 (CEI)
Dimensions in mm
15.49
14.99
32.26
31.24
4.06
3.56
0.89
0.38
13.97
12.70
3.81
3.18
0.38
0.20
17.02
15.24
1.65
1.02
0.58
0.38
2.54
27.94
24
13
technical drawings
according to DIN
specifications
13041
1
12
9.15
8.65
Package SO24
Dimensions in mm
15.55
15.30
7.5
7.3
2.35
0.25
0.10
0.25
0.4
10.50
10.20
1.27
13.97
24
13
technical drawings
according to DIN
specifications
13037
1
12
TELEFUNKEN Semiconductors
25 (26)
Rev. A1, 31-Jan-97
Preliminary Information
U4084B
Ozone Depleting Substances Policy Statement
It is the policy of TEMIC TELEFUNKEN microelectronic GmbH to
1. Meet all present and future national and international statutory requirements.
2. Regularly and continuously improve the performance of our products, processes, distribution and operating systems
with respect to their impact on the health and safety of our employees and the public, as well as their impact on
the environment.
It is particular concern to control or eliminate releases of those substances into the atmosphere which are known as
ozone depleting substances (ODSs).
The Montreal Protocol (1987) and its London Amendments (1990) intend to severely restrict the use of ODSs and
forbid their use within the next ten years. Various national and international initiatives are pressing for an earlier ban
on these substances.
TEMIC TELEFUNKEN microelectronic GmbH semiconductor division has been able to use its policy of
continuous improvements to eliminate the use of ODSs listed in the following documents.
1. Annex A, B and list of transitional substances of the Montreal Protocol and the London Amendments respectively
2. Class I and II ozone depleting substances in the Clean Air Act Amendments of 1990 by the Environmental
Protection Agency (EPA) in the USA
3. Council Decision 88/540/EEC and 91/690/EEC Annex A, B and C (transitional substances) respectively.
TEMIC can certify that our semiconductors are not manufactured with ozone depleting substances and do not contain
such substances.
We reserve the right to make changes to improve technical design and may do so without further notice.
Parameters can vary in different applications. All operating parameters must be validated for each customer
application by the customer. Should the buyer use TEMIC products for any unintended or unauthorized
application, the buyer shall indemnify TEMIC against all claims, costs, damages, and expenses, arising out of,
directly or indirectly, any claim of personal damage, injury or death associated with such unintended or
unauthorized use.
TEMIC TELEFUNKEN microelectronic GmbH, P.O.B. 3535, D-74025 Heilbronn, Germany
Telephone: 49 (0)7131 67 2831, Fax number: 49 (0)7131 67 2423
26 (26)
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
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