January 1998
Figure 1. Block diagram.
24 pin DIP
PBL 388 13
Voice-switched Speakerphone Circuit
with built in loudspeaker amplifier
24 pin SO
Description.
1
The PBL 388 13 contains all the necessary circuitry, amplifiers, detectors,
comparator and control functions to implement a high performance, voice-switched,
loudspeaking, "hands-free " telephone. The gain dynamics (attenuation between
channels) is selectable (25dB or 50dB) via a separate pin. A background noise detector
in the transmitting channel reduces the influence of continuous external noise signals
to the switching .
The PBL 388 13 is designed for telephone systems that are either powered from
the telephone line or from a mains powered constant voltage dc. supply. The circuit
contains a transformerless audio power amplifier with a current supply circuitry
(patented) that eliminates the need of inductors. Automatic volume attenuation in the
power amplifier extends the operating range at low line currents. A special feature in
this circuit is that the power amplifier volume control can be implemented either as an
ac. potentiometer control or as a digital control by a
-processor (dc. control).
Filtering is possible of both, the audio and the speech switching control signals,
in both transmitter and receiver channels.
Key Features
Minimum of external components
needed for function.
Selectable gain dynamics. (25 or 50
dB)
Direct telephone line powered solution
(patented).
Low power consumption:
1mA at 3.3V
(typical) for speech switching, audio
power amplifier quiscent current
1mA.
Drives an 25 - 50 ohm loudspeaker
without a transformer.
Background noise compensation in the
transmitting channel with hold function
at receive.
Input amplifiers of both channels have
balanced inputs.
Exellent noise performance.
Encapsulated in 24 pin plastic "skinny"
DIP and 24 pin SO .
+
F2
F3
F6
F5
F1
PBL 388 13
F4
22
21
3
1
2
7
6
8
9
13
14
11
23
16
17
18
20
24
4
+
+
+
19
10
12
Ref.
5
15
Control
PBL 388 13
PBL 388 13
2
PBL 388 13
Maximum Ratings
Parameter
Symbol
Min
Max
Unit
Speech switch supply current
I
D
10
mA
Speaker amplifier supply current
I
+L
130
mA
Voltage pin 1-14
-0,5
Vpin
15
+0.5
V
Operating temperature
T
Amb
-20
+70
C
Storage temperature
T
Stg
-55
+125
C
Figure 3. Test circuit.
Reference figure No. 3.
Figure 4. Test circuit.
Reference figure No. 4.
Figure 2. Isolation and
measurement of V
Ref
.
Ref fig No.2.
V +
GND
V Ref
+
PBL 388 13
V+
D
I
RxDetin
RxDetout 9
15
16
10
100nF
14
V
Txout
CTR
V
V
CMP
V
TxDet
V
Rxout
+
10
F
CMP
CTR
GND
6
8
9
24
16
7
Det
N
TxDetout
4 Txout
RxDetout
in
-Rx
2
1
F
Rxin
I
V
Rxin
+
NDet
R
CTR
C
TxDet
I
TxDet
0,1
F
C
RxDet
V
RxDet
I
CTR
V
NDet
RxDet
I
PBL 388 13
11
Rxout
R
Rxout
10
F
+
1
3
5
F2out
13
1
F
Txout
R
100
F/16V
V+
15
+
V+
D
I
I
Txin
V
Txin
4.7
F
+
+
+
+
+
TxDetin
-Tx in
+Txin
in
+Rx
10
Rx Detin
12
F5out
10
F
+
F5out
R
F5out
C
Rx
1
F
+
10
F
+
F2out
R
F2out
C
Tx
+
LSP 18
+ L 20
C 17
+
100
16 V
F
1000
16 V
F
0.015
used only
with inductive load
I
+L
GND
16
R
22
E
R
21
DC
V
in
Input
23 LSP
in
50
Load
PBL 388 13
1
F
0.015
VOL 19
V
out
V
A
Power
amplifier
supply
+
-
I
VOL
3
PBL 388 13
Electrical Characteristics
f = 1 kHz, T = 25
C, R
CTR
=0, C
TxDet
= 0, R
Txout
=
, R
Rxout
=
, R
F2out
=
, R
F5out
=
, C
Tx
= 0, C
Rx
= 0, C
RxDet
= 0 and
I
D
=1.0mA unless otherwise noted.
Ref.
Parameter
fig.
Condition
Min.
Typ.
Max.
Unit.
Speech control section
Terminal voltage, V
+
3
I
D
= 1.0mA
3.3
V
Internal reference voltage, V
Ref
2
1.96
V
Frequency response for all amplifiers
3
200 - 3400 Hz, Relative 1 kHz
-1
1
dB
Transmit gain, 20
10
log(V
Txout
/V
Txin
)
3
V
CMP
= V
Ref
- 0.1 V
40.5
43
dB
V
CMP
= V
Ref
+ 0.1 V
-7
-4.5
dB
V
CMP
= V
Ref
- 0.1 V R
CTR
=100k, V
CTR
=V+
40.5
43
dB
V
CMP
= V
Ref
+ 0.1 V R
CTR
=100k, V
CTR
=V+
18
20.5
dB
Receive gain, 20
10
log(V
Rxout
/V
Rxin
)
3
V
CMP
= V
Ref
+ 0.1 V
26.5
29
dB
V
CMP
= V
Ref
- 0.1 V
-21
-18.5
dB
V
CMP
= V
Ref
+ 0.1 V R
CTR
=100k, V
CTR
=V+ 26.5
29
dB
V
CMP
= V
Ref
- 0.1 V R
CTR
=100k, V
CTR
=V+
4
6.5
dB
Max transmit detector gain,
3
V
TxDet
< 200 mV
p
, C
Rx
= 100nF
20
10
log(V
Txdet
/V
Txin
)
V
CMP
= V
Ref
- 0.1 V
67
dB
V
CMP
= V
Ref
+ 0.1 V
36.5
42
dB
Max receive detector gain,
3
V
RxDet
< 200 mV
p
, C
Tx
= 100nF
20
10
log(V
Rxdet
/V
Rxin
)
V
CMP
= V
Ref
+0.1 V
53
dB
V
CMP
= V
Ref
- 0.1 V
22.5
28
dB
Background noise rectifier gain, (note 1) 3
V
CMP
= V
Ref
- 0.1 V, C
Txdet
=1
F
6.0
dB
V
CMP
= V
Ref
+ 0.1 V, C
Txdet
=1
F
Hold
+ Tx
In
input impedance
3
80
100
120
k
- Tx
In
input impedance
3
2.4
3.0
3.6
k
+ Rx
In
input impedance
3
120
140
160
k
- Rx
In
input impedance
3
16
20
24
k
Tx
Out
ac, load impedance
3
10
k
Rx
Out
ac, load impedance
3
10
k
F2
Out
ac, load impedance
3
10
k
F5
Out
ac, load impedance
3
10
k
Transmitter channel output swing, v
TxOut
3
2% distortion,R
Txout
=R
Rxout
=10k
500
mV
p
Receiver channel output swing, v
RxOut
3
2% distortion,R
Txout
=R
Rxout
=10k
500
mV
p
Transmitter output noise, v
TxOut
3
V
CMP
= V
Ref
- 0.1 V, v
TxIn
= 0 V
-75
dB
psof
Receiver output noise, v
RxOut
3
V
CMP
= V
Ref
+ 0.1 V, v
RxIn
= 0 V
-80
dB
A
Tx
Det
sink current, I
TxDetOut
3
V
TxDetIn
= V
Ref
+ 0.1 V
-6.0
-2.5
mA
Rx
Det
source current, I
RxDetOut
3
V
RxIn
= V
Ref
- 0.1 V
2.5
6.0
mA
Tx
Det
source current, I
TxDet
3
V
CMP
= V
Ref
- 0.1 V
30
A
Rx
Det
sink current, I
RxDetOut
3
V
RxDetIn
= V
Ref
+ 0.1 V
-30
A
Tx
Det
swing relative to V
Ref
, V
TxDetOut
3
V
TxDetIn
= V
Ref
+ 0.1 V
(note 2)
-0.7
V
Rx
Det
swing relative to V
Ref
, V
RxDetOut
3
V
RxDetIn
= V
Ref
- 0.1 V
(note 2)
+0.7
V
N
Det
sink current (fast charge), I
NDet
3
V
TxDetIn
= V
Ref
- 0.1 V
-3
-1
mA
V
CMP
= V
Ref
- 0.1 V
N
Det
source current, I
NDet
3
V
TxDetIn
= V
Ref
+ 0.1 V
3
5
7
A
V
CMP
= V
Ref
- 0.1 V
4
PBL 388 13
Ref.
Parameter
fig.
Conditions
Min.
Typ.
Max.
Unit.
N
Det
leakage current (hold), I
NDet
3
V
TxDetIn
= V
Ref
- 0.1 V,
-100
nA
V
CMP
= V
Ref
+ 0.1 V,
N
Det
swing relative to V
Ref
, V
NDet
3
V
TxDetIn
= V
Ref
+ 0.1 V,
0.45
V
V
CMP
= V
Ref
- 0.1 V
CMP (comparator) sensitivity,
3
Tx mode = max Tx gain,
40
80
mV
transmit (Tx) mode to receive 13
Rx mode = max Rx gain
(Rx) mode or vice versa
CTR voltage for 25 dB dynamics, V
CTR
3,15 R
CTR
=100k
V
+
V
CTR voltage for mute, V
CTR
3,15
1.1
1.6
V
CTR voltage for disable, V
CTR
3,15
0.9
V
Loudspeaker amplifier
Operating voltage, V
A
4
2.5
12
V
Current consumption (no signal), I
+L
4
V
A
= 3.0 V
1
2.3
mA
4
V
A
= 5.0 V
2
mA
4
V
A
= 12.0 V
4
9
mA
17
R
E
= 1.5 k, V
Line
= 3.0 V (Note 3)
1.3
2.4
mA
V
RDC
= 0.35 V
17
R
E
= 1.5 k, V
Line
= 12.0 V (Note 3)
7.5
14
mA
V
RDC
= 5.0
Current consumption
4
V
A
= 3.0 V
7
mA
(output swing at 5% dist.)
4
V
A
= 5.0 V
13
mA
4
V
A
= 12.0 V
30
mA
Swing at 5% dist., V
Out
4
V
A
= 3.0 V
0.6
0.85
V
p
4
V
A
= 5.0 V
1.5
1.7
V
p
4
V
A
=12.0 V
3.6
4.0
V
p
Gain
4
V
A
=5.0 V, I
VOL
= 0
34.5
36.5
38.5
dB
Frequency response
4
200 to 3400 Hz, relative 1kHz,
-1
1
dB
Amplifier power efficiency (5% dist), n
4
V
A
= 3.0 to 12.0 V,
n = 100 P
Load
/P
Supply
40
%
Input impedance pin 23
4
24
30
36
k
Notes
V
NDet
- V
Ref
1.
20
10
log (
)
V
TxDet
- V
TxDetO
V
NDet
= voltage at noise detector output
V
Ref
= reference voltage (about 2 V) see figure 2.
V
TxDet
= Voltage at transmit detector output.
V
TxDetO
=
voltage at transmit detector output at the point
when the voltage at the noise detector starts
moving when a signal at transmit channel input is
gradually increased (threshold, typical value 30 mV)
2.
Depends on V
+
. Channels are tracking.
3.
V
Line
=V
A
+V
RDC
Figure 5. Power amplifier distortion
0.5
1.0
1.5
2.0
2.5
3.0
3.5
2
4
6
8
10
12
14
16
18
5%
2%
f = 1 kHz
V
out
V
Line
0
5
PBL 388 13
Figure 6. Pin configuration.
Pin Descriptions
Refer to figure 6. (24 pin DIP and 24 pin SO package)
24 pin SO
Pin
Symbol
Description
1
-Txin
Transmitter channel negative input.
Input impedance 3.16 kohm.
2
+Txin
Transmitter channel positive input.
Input impedance 100 kohm.
3
F2out
Output of the second amplifier in the
transmitter channel.
4
Txout
Transmitter channel output. Min. ac
load impedance 10 kohm.
5
TxDetin
Input of the transmitter channel signal
detector. Input impedance 13 kohm.
6
TxDetout Output of the transmitter channel signal
detector. Goes nagative referred to the
internal ref. voltage of appx. 2V when a
transmitter signal is present.
7
NDet
Background noise detector output.
Goes positive referred to the internal ref.
voltage of app. 2V when a background
noise signal is present
8
CMP
Comparator input. External resistance
to this point should not be less than
50 kohm. Summing point to the different
detector outputs.
9
RxDetout Output of the receiver channel signal
detector. Goes positive referred to the
internal ref. voltage of appx. 2V when a
receiver signal is present
10
RxDetin
Input of the receiver channel signal
detector. Input impedance 13 kohm.
Pin
Symbol
Description
11
Rxout
Receiver channel output. Min. ac load
impedance 10 kohm.
12
F5out
Output of the second amplifier in the
receiver channel.
13
+Rxin
Receiver channel positive input. Input
impedance 140 kohm.
14
-Rxin
Receiver channel negative input. Input
impedance 20 kohm.
15
V+
Supply of the speech switching circuitry.
A shunt regulator, voltage apprx. 3.3V at
1.0mA.
16
GND
System ground (- line ).
17
-C
18
LS
Loudspeaker power amplifier output.
19
VOL
Volume control input. By sourcing a
current of appx. 0-40
A into this pin the
gain can be reduced.
20
+L
Positive supply for the loudspeaker
amplifier.
21
RDC
Power ampl. supply options. Pins - C,
22
RE
RDC and RE are explained in the text.
23
LSPin
Loudspeaker amplifier signal input. Input
impedance 30 kohm.
24
CTR
Control input for gain dynamics
(25 or 50dB), mute and disable.
1
2
3
4
5
6
7
8
9
10
11
22
21
20
19
18
17
16
15
14
13
12
23
24
-Txin
+Txin
F2out
Txout
TxDetin
TxDetout
N Det
CMP
RxDetout
RxDetin
Rxout
F5out
+Rxin
-Rxin
V+
-C
LSP
+L
R
DC
R
E
VOL
LSPin
GND
CTR
1
2
3
4
5
6
7
8
9
10
11
22
21
20
19
18
17
16
15
14
13
12
23
24
-Txin
+Txin
F2out
Txout
TxDetin
TxDetout
N Det
CMP
RxDetout
RxDetin
Rxout
F5out
+Rxin
-Rxin
V+
-C
LSP
+L
R
DC
R
E
VOL
LSP in
GND
CTR
24 pin DIP
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