PBL 385 70
Universal Speech Circuit
20-pin plastic SO
18-pin plastic DIP
September 1997
Figure 1. Functional diagram. DIP package.
1
Description.
PBL 38570 is a monolithic integrated speech transmission circuit for use in electronic
telephones. It is designed to accomodate either a low impedance dynamic or an electret
microphone. A separate input for DTMF dialling tones that is controlled by a mute signal,
and a signal summing point at the transmitter input, are available.
An internally preset line length compensation can be adjusted with external resistors
to fit into different current feed systems as for ex. 48 V, 2 x 200 ohms, 48 V, 2 x 400 ohms
and 48 V, 2 x 800 ohms. The line length compensation can be shut off in either high or
low gain mode. Application dependent parameters such as line balance, side tone level,
transmitter and receiver gains and frequency responces are set independently by
external components which means an easy adaption to various market needs.
The setting of the parameters if carried out in certain order will counteract the
interaction between the settings.
A number of different DC - supplies are provided to feed microphones and diallers.
Key features.
Minimum number of external
components, 7 capacitors and 11
resistors.
Easy adaption to various market
needs.
Mute control input for operation with
DTMF - generator.
A separate input for DTMF tones
controlled by mute.
Transmitter and receiver gain
regulation for automatic loop loss
compensation.
Extended current and voltage range
5 - 130 mA, down to 2 V.
Differential microphone input for
good balance to ground.
Balanced receiver output stage.
Stabilized DC - supplies for low
current CMOS diallers and electret
microphones.
18 - pin DIP and 20 - pin SO packa-
ges.
Short start up time.
Excellent RFI performance.
PBL 38570
PBL 38570
1. Line impedance and radio interference suppression.
2. Transmit gain and frequency response network.
3. Receive gain and frequency response network.
4. Side tone balance network.
5. DC-supply components.
17
14
2
3
11
12
13
18
16
AM
AT
5
AR
15
4
+
10
AD
1
PBL 385 70
7
9
Sense input
DTMF
input
+
6
Mic.
8
DC-supply
+
Mute
(active low)
DC-output for
external devices
Telephone
line
5
2
4
3
1
Gain
regulation
PBL 385 70
2
Figure 2. Test set up without rectifier
bridge.
Figure 3. Test set up with rectifier
bridge.
Figure 4. Circuit with external compon-
ents for test set up.
* Not used in test set up.
18 pin DIP package.
Maximum Ratings
Parameter
Symbol
Min
Max
Unit
Line voltage, t
p
= 2 s
V
L
0
18
V
Line current, continuous DIP
I
L
0
130
mA
Line current, continuous SO package
I
L
0
100
mA
Operating temperature range
T
Amb
-40
+70
C
Storage temperature range
T
Stg
-55
+125
C
No input should be set on higher level than pin 4 (+C).
+
= 350
+ LINE
- LINE
ARTIFICIAL
LINE
I L
V
2
V1
V
L
R = 0-4k
L
0 ohm when artificial
line is used
MUTE
PBL 385 70
with external
components
See fig. 4
Z
Mic = 350
Z
Rec
MIC
REC
R
feed = 400
+400
600
C
E = 48.5V
V 3
V4
I
DC1
C = 1
F when artificial line is used
470
F when no artificial line
V
M
DC2
I
V
DC1
V
DC2
5H+5H
+
I
M
+
+ LINE
- LINE
I
L
V
2
V
1
V
L
R = 0 - 4k
L
MUTE
PBL 385 70
with external
components
See fig. 4
Z
Mic
Z
Rec
MIC
REC
R
feed = 400
+400
600
+
E = 50.0V
V
3
V
4
1
F
V
M
Uz= 15-16V
5H+5H
I
DC1
DC2
I
V
DC1
V
DC2
= 350
= 350
I
M
17
14
2
3
11
12
13
18
16
AM
AT
5
AR
15
4
+
10
AD
1
PBL 385 70
7
9
Sense input
DTMF
input
+
6
Gain
regulation
Mic.
350
8
DC-supply
+
Mute
(active low)
DC-output for
external devices
2.7k
47
F
*
*
18k
22k
100n
75
910
560
11k
100n
6.2k
11k
10
62k
47
F
15n
Rec.
350
310
220n
-Line
+Line
910
47n
C1
C2
C3
C5
C6
C7
R1
R2
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R3
R14
R16
C9
PBL 385 70
3
Electrical Characteristics
At T
Amb
= + 25
C. No cable and line rectifier unless otherwise specified.
Parameter
fig.
Conditions
Min
Typ
Max
Unit
Line voltage, V
L
2
I
L
= 15 mA
3.3
3.7
4.1
V
2
I
L
= 100 mA
11
13
15
V
Transmitting gain, note 1
20
10
log (V
2
/ V
3
); 1 kHz
2
R
L
= 0
41
43
45
dB
2
R
L
= 400
43.5
45.5
47.5
dB
2
R
L
= 900
- 2.2 k
46
48
50
dB
Transmitting range of
2
1 kHz, R
L
= 0 to 900
3
5
7
dB
regulation
Transmitting frequency
2
200 Hz to 3.4 kHz
-1
1
dB
response
Transmitter input impedance
2
1 kHz
13.5
17
20.5
k
pin 3
Transmitter dynamic output
2
200 Hz - 3.4 kHz
1.5
V
p
2% distortion, I
L
= 20 - 100 mA
Transmitter max output
2
200 Hz - 3.4 kHz
3
V
p
I
L
= 0 - 100 mA, V
3
= 0 - 1 V
Transmitter output noise
2
Psoph-weighting, Rel 1 V
rms
, R
L
= 0
-75
dB
Psoph
Microphone input impedance
2
1 kHz
1.7(//2.7)
k
pin 12 (14),13 (15)
note 3
Receiving gain, note 1
20
10
log (V
4
/ V
1
); 1 kHz
2
R
L
= 0
-18.5
-16.5
-14.5
dB
2
R
L
= 400
-16
-14
-12
dB
2
R
L
= 900
- 2.2 k
-13.5
-11.5
-9.5
dB
Receiving range of regulation
2
1 kHz, R
L
= 0 to 900
3
5
7
dB
Receiving frequency response
2
200 Hz to 3.4 kHz
-1
1
dB
Receiver input impedance
2
1kHz
30.4
38
45.6
k
Receiver output impedance
2
1 kHz,
3(+310), note 3
Receiver dynamic output
2
200 Hz - 3.4 kHz
0.5
V
p
note 2
2% distortion, I
L
= 20 - 100 mA
Receiver max output
3
Measured with line rectifier
0.9
V
p
200 Hz - 3.4 kHz, I
L
= 0 - 100 mA,
V
1
= 0 - 50 V
Receiver output noise
2
A-weighting, Rel 1V
rms
, with cable
-85
dB
A
0 - 5 km, = 0.5 mm, 0 - 3 km,
= 0.4 mm
Mute input voltage
2
0.3
V
at mute (active low)
DC-supply voltage
2
I
L
= 20 - 100 mA
I
DC
= 0 mA
2.1
2.35
2.6
V
I
DC
= 2 mA
1.95
2.2
2.6
V
DC-supply current, pin 8.
2
2
mA
DC-output pin 8 input
4
V
DC
= 2.35 V
0.1
A
leakage current (no supply)
DTMF transmitting gain
2
V
M
= 0.3 V, 1 kHz
24.5
26.5
28.5
dB
DTMF input impedance
2
1 kHz
20
25
30
k
Notes
1. Adjustable to both higher and lower values with external components.
2. The dynamic output can be doubled, see applications information.
3. External resistor in the test set up.
Ref.
PBL 385 70
4
Figure 5. Pin configuration.
18-pin DIP
20-pin SO
}
}
+L
TO
TI
+C
Mute
GR
DCS
DCO
DR
RI
-L
MI 2
MI 1
MO
1
2
3
4
5
6
7
8
16
15
14
13
12
11
DCC
DI
9
10
RE 2
RE 1
18
17
1
2
3
4
5
6
7
8
19
18
17
16
15
14
13
+L
TO
TI
+C
Mute
GR
DCS
DCO
RE 2
RE 1
DR
RI
-L
MI 2
MI 1
MO
9
12
10
11
DCC
NC
DI
NC
4
5
17
16
20
Pin Descriptions
Refer to figure 5.
DIP
SO
Name
Function
1
1
+L
Output of the DC-regulator and transmit amplifier, connected to the line through a polarity
guard diode bridge.
2
2
TO
Output of the transmit amplifier, connected through a resistor of 47 to 100 ohm to -L,
sets the DC-characteristics of the circuit. The output has a low AC output impedance and the
signal is used to drive a side tone balancing network.
3
3
TI
Input of transmit amplifier. Input impedance 17 kohm
20 %.
4
4
+C
Positive power supply terminal for most of the circuitry inside the PBL 385 70 (about 1 mA current
consumption). The +C pin must be connected to a decoupling capacitor of 47
F to 150
F.
5
5
Mute
When low, speech circuit is muted and the DTMF input is enabled. Maximum voltage (at mute) is
0.3 V, current sink requirement of external driver is min. 50
A.
6
6
GR
Control input for the gain regulation circuitry.
7
7
DCS
Sense input to the DC-supply.
8
8
DC1
Output from the DC-supply.
9
9
DC2
Control of the DC-supply.
10
12
DI
Input for the DTMF-signal. Input impedance is 25 kohm
20 %.
11
13
MO
Output of the microphone amplifier or DTMF-amplifier.
12
14
MI 1
Inputs to the microphone amplifier. Input impedance 1.7 kohm
20 %.
13
15
MI 2
14
16
-L
The negative power terminal, connected to the line through a polarity guard diode bridge.
15
17
RI
Input of receiver amplifier. Input impedance is 38 kohm
20 %.
16
18
DR
Control input for the receiver amplifier driving capacity.
17
19
RE 1
Receiver amplifier outputs. Output impedance is approximately 3 ohm.
18
20
RE 2
10
NC
11
NC
PBL 385 70
5
Functional description
Design procedure
; ref. to fig.4.
The design is made easier through that all settable parameters are returned to ground (-line) this feature differs it from bridge
type solutions. To set the parameters in the following order will result in that the interaction between the same is minimized.
1.
Set the circuit impedance to the line, either 600
or complex. (R3 and C1). C1 should be big enough to give low
impedance compared with R3 in the telephone speech frequency band. Too large C1 will make the start-up slow.
See fig. 6.
2.
Set the DC-characteristic that is required in the PTT specification or in case of a system telephone in the PBX
specification (R6). There are also internal circuit dependent requirements like supply voltages etc.
3.
Set the attac point where the line length regulation is supposed to cut in (R1 and R2). Note that in some countries
the line length regulation is not allowed. In most cases the endresult is better and more readily achieved by using
the line length regulation (line loss compensation) than without. See fig. 12.
4.
Set the transmitter gain and frequency response.
5.
Set the receiver gain and frequency response. See text how to limit the max. swing to the earphone.
6.
Adjust the side tone balancing network.
7.
Set the RFI suppression components in case necessary. In two piece telephones the often "helically"
wound cord acts as an aerial. The microphone input with its high gain is especially sensitive.
8.
Circuit protection. Apart from any other protection devices used in the design a good practice is to connect a 15V 1W
zener diode across the circuit , from pin 1 to -Line.
Impedance to the line
The AC- impedance to the line is set by
R3, C1 and C2. Fig.4. The circuits relatively
high parallel impedance will not influence
it to any noticeable extent. At low
frequencies the influence of C1 can not be
neglected. Series resistance of C1 that is
dependent on temperature and quality will
cause some of the line signal to enter pin
4. This generates a closed loop in the
transmitter amplifier that will create an
active impedance thus lowering the
impedance to the line. The impedance at
high frequencies is set by C2 that also
acts as a RFI suppressor.
In many specifications the impedance
towards the line is specified as a complex
network. See fig. 6. In case a). the error
signal entering pin 4 is set by the ratio
Rs/
R19 (909
), where in case b). the ratio at
high frequencies will be Rs/220
because
the 820
resistor is bypassed by a
capacitor. To help up this situation the
complex network capacitor is connected
directly to ground (-line), case c). making
the ratio Rs/220
+820
and thus less-
ening the error signal. Conclusion: Connect
like in case c) when complex impedance
is specified.
1
2
+Line
R3
R6
PBL 385 70
+
3
C1
C2
-Line
Rs
1
How to connect a
complex network.
Example:
a)
b)
c)
4
Figure 6. AC-impedence
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