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| 型號： | TCA3388FP |
| 廠商： | MOTOROLA INC |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | TELEPHONE LINE INTERFACE |
| 中文描述： | TELECOM-SLIC, PDSO20 |
| 封裝： | PLASTIC, SOIC-20 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 274K |
| 代理商： | TCA3388FP |
TCA3388
9
MOTOROLA ANALOG IC DEVICE DATA
C
R
R
R
R
C
SAO
LAI
Gnd
Figure 7. Derived Network for Z21 in Case of
Complex Set Impedance
a
b
b
v
Rv
w
w
Rv
R1 x Z0
Rb– R1
2 Ra
R
w
R1 x Z0 Ra– R1
4
RbRa
2x C
b
R1 x Z0
Rb– R1
C
w
4 R
b
TRANSMIT
When a current is injected on Pin LAI, via the loop
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 (VLine) depends on the signal
current injected in LAI (ILAI) according to:
VLine
–ILAIx
Z0 x ZLine
Zin
ZLine
With this relation, a simplified replacement circuit can be
made for the transmit amplifier (see Figure 8). Here the
product of ILAI and Z0 is replaced by one voltage source.
Z
–I
Z
Figure 8. Replacement Diagram for
the Transmit Amplifier
Line
in
LAI*Z0
VLine
The microphone signal current is derived from the
microphone signal according to the schematic in Figure 9.
R
C
R
R
Mic
TXI
Microphone
Handset
Ku
I
Line AGC
TCA3388
Mute
Figure 9. Microphone Amplifier Input Stage
V
Mic
Mic
u
Cu
Iu
TXI
LAI
CC
The input stage of Figure 9 consists of a current amplifier
with transfer Ku, an input impedance of 1.0 k (RTXI), 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 Iu within the telephony
speech band is derived from the microphone signal according
Iu
Vu
Ru
RMic
RTXI
Vu
Ru
With: Vu = signal of the microphone only loaded with RMic
The overall gain from microphone to line (ATX) now follows
as
ATX
VLine
Vu
Ku
Ru
x
Z0 x ZLine
Zin
ZLine
Practically, the gain can be varied only with Z0, Ru and
RMic.
The TCA3388 offers the possibility to mute the
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.
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