PBL 388 12
1
October 1999
PBL 388 12
Voice-switch circuit for
Handsfree speakerphone TAM
Description
The PBL 388 12 contains all the necessary circuitry, amplifiers, detectors, comparators
and control functions to implement a high performance, voice-switched, "hands-free "
function in an answering machine. The gain dynamics (attenuation between channels)
is settable (25dB or 50dB) via CTR pin that also control two mute levels. A background
noise detector in the transmitting channel reduces the influence of continuous noise sign-
als.
The PBL 388 12 is designed for answering machines that are either powered from the
telephone line or from a mains powered dc. supply.
Filtering of both the audio and control signals in both transmitter and receiver channels
possible.
An external loudspeaker amplifier has to be used, normally the same as used for the
answering machine.
Control
F2
F3
F6
F5
F1
PBL 388 12
F4
4
2
3
8
7
9
10
14
12
1
5
16
+
+
+
11
13
Ref.
6
15
PBL388 12
16-pin SO
Figure 1. Block diagram. ( SO - package )
18-pin DIP
PBL388 12
Key Features
Settable gain dynamics (25 or 50
dB).
Low power consumption, totally
1.0mA at 3.3V typical.
Background noise compensation in
the transmitting channel with hold
function.
Exellent noise performance.
Both channel input amplifiers have
balanced inputs.
Minimum of external components
needed for function.
16-pin SO and 18-pin DIP
encapsulation.
All figures in this paper refer to 16-pin SO package.
PBL 388 12
2
Maximum Ratings
Parameter
Symbol
Min
Max
Unit
Speech switch supply current
I
D
10
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 2. Isolation and measurement of V
Ref
. Reference figure No.2.
CTR
V
V
CMP
V
TxDet
V
Rxout
CMP
CTR
GND
7
9
10
1
16
8
Det
N
TxDetout
5 Txout
Rx Detout
3
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 12
12
Rxout
R
Rxout
10
F
+
2
4
6
F2out
14
100
F/16V
V+
15
V+
+
+
TxDetin
-Tx in
+Tx in
in
-Rx
11
Rx Detin
13
F5out
10
F
+
F5out
R
F5out
C
Rx
V
Txout
+
10
F
Txout
R
+
D
I
I
Txin
V
Txin
4.7
F
+
1
F
+
10
F
+
F2out
R
F2out
C
Tx
+
V +
GND
V Ref
+
PBL 388 12
V+
D
I
RxDetin
RxDetout 10
15
16
11
100nF
PBL 388 12
3
Electrical Characteristics
f = 1 kHz, T = 25
C, R
CTR
=0, C
TxDet
= 0, R
Txout
=
, R
Rxout
=
, R
F2out
=
, R
F5out
=
, R
Tx
= 0, R
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
41.5
44
dB
V
CMP
= V
Ref
+ 0.1 V
-6
-3.5
dB
V
CMP
= V
Ref
- 0.1 V R
CTR
=100k, V
CTR
=V+
41.5
44
dB
V
CMP
= V
Ref
+ 0.1 V R
CTR
=100k, V
CTR
=V+
19
21.5
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
Tx
= 100nF
20
10
log(V
Txdet
/V
Txin
)
V
CMP
= V
Ref
- 0.1 V
67.5
dB
V
CMP
= V
Ref
+ 0.1 V
37
42.5
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
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
=25k
500
mV
p
Receiver channel output swing, v
RxOut
3
2% distortion,R
Txout
=R
Rxout
=25k
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
-75
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
-4.5
-1.5
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
PBL 388 12
4
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
CMP
= V
Ref
- 0.1 V,
-0.45
V
V
TxDetIn
= V
Ref
+ 0.1 V
CMP (comparator) sensitivity,
3
Tx mode = max Tx gain,
50
100
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
V
CMP
= V
Ref
0.35 V, R
CTR
=100k
V
+
V
CTR voltage for mute, I
CTR
3
V
CMP
= V
Ref
0.35 V
A
CTR voltage for disable, V
CTR
3
0.55
V
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 1.9 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.
PBL 388 12
5
Figure 4. Pin configuration.
Pin Descriptions:
Refer to figure 4. (16-pin SO and 18-pin DIP package)
16-pin SO
SO DIP Symbol Description
1
16
CTR
Control input for gain dynamics
(25 or 50dB), mute and disable.
2
17
-Txin
Transmitter channel negative input.
Input impedance 3 kohm.
3
18
+Txin
Transmitter channel positive input.
Input impedance 100 kohm.
4
1
F2out
Output of the second amplifier in the
transmitter channel.
5
2
Txout
Transmitter channel output. Min. ac
load impedance 10 kohm.
6
3
TxDetin
Input of the transmitter channel signal
detector. Input impedance 13 kohm.
7
4
TxDetout
Output of the transmitter channel signal
detector. Goes nagative referred to the
internal ref. voltage of app. 2V when a
transmitter signal is present.
8
5
NDet
Background noise detector output.
Goes positive referred to the internal ref.
voltage of app. 2V when a backgrounud
noise signal is present
SO DIP Symbol Description
9
6
CMP
Comparator input..
Summing point to the different
detector outputs.
10
7
RxDetout
Output of the receiver channel signal
detector. Goes positive referred to the
internal ref. voltage of app. 2V when a
receiver signal is present
11
8
RxDetin
Input of the receiver channel signal
detector. Input impedance 13 kohm.
12
9
Rxout
Receiver channel output. Min. ac load
impedance 10 kohm.
13
10
F5out
Output of the second amplifier in the
receiver channel.
11 +Rxin
Receiver channel positive input. Input
impedance 140 kohm.
14
12
-Rxin
Receiver channel negative input. Input
impedance 20 kohm.
15
13
V+
Supply of the speech switching
circuitry. A shunt regulator, voltage
apprx. 3.3V at 1.0mA.
16
14
GND
System ground.
15
NC
Not connected.
18-pin DIP
Pin Pin
Pin Pin
F2out
Txout
TxDetin
TxDetout
N Det
CMP
RxDetout
Rx Detin
CTR
NC
GND
+V
-Rxin
+Rxin
1
2
3
4
5
6
7
8
16
15
14
13
12
11
F5out
9
10
+Txin
-Txin
18
17
Rxout
1
2
3
4
5
6
7
8
16
15
14
13
-Txin
CTR
NDet
F2out
+V
RxDetout
+Txin
TxDetin
-Rxin
Rxout
CMP
9
12
10
11
F5out
GND
TxDetout
RxDetin
Txout
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