September 1997
PBL 385 70
Universal Speech Circuit
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.
•
•
•
•
•
•
•
•
•
•
•
1
DTMF
input
10
AD
AT
AR
17
Mic.
13
DC-supply
AM
18
Telephone
line
8
Mute
(active low)
9
7
Sense input
6
5
11
3
2
15
16
14
+
4
P
B
20-pin plastic SO
18-pin plastic DIP
12
L
P
B
L
+
DC-output for
external devices
+
2
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.
Figure 1. Functional diagram. DIP package.
1
38
57
5
Gain
regulation
4
3
1
0
38
57
PBL 385 70
0
ERICSSON [ ERICSSON ]
