tca3388 Freescale Semiconductor, Inc, tca3388 Datasheet - Page 9

• Manufacturer Part Number: tca3388
• Description: Advance Information Telephone Line Interface
• Manufacturer: Freescale Semiconductor, Inc

TRANSMIT
depicted in Figure 6, a signal is created on the line. In this
way the microphone signals and DTMF signals (from an
external source) are transmitted. It can be derived that the
signal voltage on the line (V Line ) depends on the signal
current injected in LAI (I LAI ) according to:
made for the transmit amplifier (see Figure 8). Here the
product of I LAI and Z0 is replaced by one voltage source.
MOTOROLA ANALOG IC DEVICE DATA
When a current is injected on Pin LAI, via the loop
With this relation, a simplified replacement circuit can be
Figure 7. Derived Network for Z21 in Case of
R
b
R
a
Figure 8. Replacement Diagram for
R v
R
C
V
C
w
Line
w
Complex Set Impedance
b
+
+
+
the Transmit Amplifier
2 R a
4 R
+
SAO
4
–I
R1 x Z0
R1 x Z0 R a – R1
R
LAI *Z0
b
–I
b
R1 x Z0
2
)
LAI
R a
x C
Z
R
in
b
)
x
R
b
v
– R1
Z
R
Z0 x Z
in
V Line
b
Gnd
)
– R1
R
Z
C
Line
w
w
Line
Z
Line
R v
LAI
TCA3388
microphone signal according to the schematic in Figure 9.
with transfer K u , an input impedance of 1.0 k (R TXI) , plus an
attenuator which reduces the signal current at high line
currents (AGC). This attenuator can be switched on/off via
the microcontroller. The input current I u within the telephony
speech band is derived from the microphone signal according
With: V u = signal of the microphone only loaded with R Mic
as
R Mic .
microphone, also called privacy mode, by making the MUT
Pin high. During pulse–dialing, the microphone bias is
switched off. Pin Mic will be made high impedance, shutting
off the microphone dc current. This reduces the current
consumption of the circuit during pulse–dialing.
Microphone
Handset
C
The microphone signal current is derived from the
The input stage of Figure 9 consists of a current amplifier
The overall gain from microphone to line (A TX ) now follows
Practically, the gain can be varied only with Z0, R u and
The TCA3388 offers the possibility to mute the
Mic
Figure 9. Microphone Amplifier Input Stage
R
Mic
A
TX
R
I u
u
+
+
C u
V
R
V u
Line
Mic
TXI
Mic
)
+
V
CC
I u
R u
V u
Ku
R u
)
R
x
TXI
R
Z
TXI
Z0 x Z
in
Ku
)
[
TCA3388
Z
Line
Line
V u
R u
Line AGC
Mute
9
I
LAI