PBL 3726/18A
Microphone selection (M1, R16)
The microphone can be either dynamic,
magnetic or electret. See figures 13, 15
and 16.
The input impedance between pin 12
(14) and 13 (15) is about 1.7 kohm with
typical variation ± 20 %.
17 (19)
18 (20)
12(14)
13(15)
11(13)
AM
Mic
50kΩ
50kΩ
-Line
Transmitting gain and frequency
response (R4, R5, C3, C4)
Figure 12. Magnetic receiver
connection.
Figure 14. Additional components for
extended low current/voltage operation.
The network gives the amplification and
frequency response for the transmitter.
R5 is used when a greater reduction of
the gain is wanted. Input impedance at
pin 3 is about 17 kohm with typical
variation ± 20 %. The sum of the
resistors R4 and R5 must not be less
than 35 kohm because of DC-current to
ground.Figure 9 shows some simple
variations of this network.
12(14)
9(9)
100Ω
DC-characteristics (R6)
+
13(15)
Sets the DC-characteristic and take care
of some of the supplied power. The
resistor have also function with the
protection of the circuit, the transmitter,
the gain regulation and the side tone.
Common values are 47 ohm to 100 ohm.
200Ω
200Ω
200Ω
47µF
12(14)
Figure 15. Connection of a magnetic
microphone.
1µF
1µF
Side tone level, receiving gain and
frequency response. (R7, R8, R9, R10,
R11, C5)
13(15)
12(14)
The network sets the side tone balance.
The network in the application is one of
many possibilities. R10 and R11 balance
together the signals that go two different
ways from the transmitter output stage
one from pin 1 and the other from pin 2.
The balance network consists of R8, R9
and C5.
14(16)
4(4)
13(15)
The example is not optimized to any
specified line, it is only given to show the
principle.
200Ω
Figure 16. Connection of a dynamic
microphone.
12(14)
13(15)
Figures 10 and 11 are examples of
balance networks. Figure 11 is especially
suited for lines with high current supply.
1µF
1µF
R13, C6, (R10, R11)
The networks gives the gain and
17(19)
18(20)
frequency response for the receiver.
Input impedance at pin 15 (17) is
about 38 kohm with a typical variation of
± 20 %. For different possibilities for the
design of the network, see the network
for the transmitter (R4, R5, C3).
14(16)
REC, R14
R14 generates the output impedance to
the magnetic earphone (figure 12). If a
dynamic earphone is used it should be
Figure 13. Electret microphone with
FET-buffer, e.g. EM80.
Figure 17. Dynamic receiver
connection.
7
ERICSSON [ ERICSSON ]
