mc34216adwf Freescale Semiconductor, Inc, mc34216adwf Datasheet - Page 11

• Manufacturer Part Number: mc34216adwf
• Description: Programmable Telephone Line Interface Circuit With Loudspeaker Amplifier
• Manufacturer: Freescale Semiconductor, Inc

Impedance
performing the ac impedance is depicted. As can be seen, it
is partly in common with the dc mask block diagram. The part
generating the dc mask is replaced by a dc voltage source
because for ac, this part has no effect.
impedance Z in equals:
equals the formula for the dc slope in Regions 1 and 3.
However, because for the dc slopes the resistive part of Z0
and Z21 are used, the actual values for Z in and the dc slopes
do not have to be equal.
or Z21 complex. When Z0 is made complex to fit the set
impedance, the transmit characteristics will be complex as
well. The complex impedance is therefore preferably made
via the Z21 network. Because Z21 is in the denominator of
the Z in formula, Z21 will not be a direct copy of the required
impedance, but a derivative of it. Figure 6 shows the derived
network to be used for Z21.
Line +
Line –
MOTOROLA ANALOG IC DEVICE DATA
In Figure 5, the block diagram of the MC34216A
When calculating the ac loop, it can be derived that the set
As can be noticed, the formula for the ac impedance Z in
A complex impedance can be made by making either Z0
Rv
Rw
Cw
Z
Rb
in
+
+
Figure 6. Derived Network for Z21 in Case
+
Z21
+
Ra
4Rb (Ra
4Rb
+
2(Ra
Figure 5. AC Stage of the MC34216A
R1 x Z0 (Ra – R1)
R1 x Z0
V
I
SAO
SAI
line
Z0
line
2
Cb
R1 x Z0
V O1
)
of Complex Set Impedance
x Cb
Rb – R1)
)
+
LAI
Rb – R1)
R1 1
SAO
V
MC34216A
+
O2
+
R1
)
Rv
Z21
Z0
LAO
Gnd
Gnd
[
Rw
Cw
R1 x Z0
T2
T3
Rv
R5
Z21
AC CHARACTERISTICS
+
MC34216A
LAI
V
C7
CC
Transmit
depicted in Figure 5, a signal is created on the line. In this
way, the microphone signals and DTMF signals from the
internal generator 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 7). Here the
product of I LAI and Z0 is replaced by one voltage source.
microphone signal according to the schematic in Figure 8.
with transfer Ku and impedance R TXI = 1.0 k
attenuator which reduces the signal current at high line
currents, the so–called line length regulated gain or line 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 to:
as:
R Mic .
Microphone
Handset
When on Pin LAI a current is injected, via the loop
With this relation, a simplified replacement circuit can be
The microphone signal current is derived from the
The input stage in Figure 8 consists of a current amplifier
With: Vu = signal of the microphone only loaded with R Mic .
The overall gain from microphone to line (A TX ) now follows
Practically, the gain can only be varied with Z0, Ru and
Cmic
Figure 8. Microphone Amplifier Input Stage
Figure 7. Replacement Diagram for the
R
A
Iu
Mic
V
TX
Ru
line
+
+
+
R
+
Transmit Amplifier
Cu
Mic
V
–I LAI *Z0
Vu
line
–I
LAI
)
Z in
TXI
MIC
+
V CC
Iu
Vu
Ru
x
Ku
Ru
Z
Z0 x Z
)
in
V line
+
–
x
)
R
Z
R
TXI
Z0 x Z
TXI
in
Z
line
line
)
Z
Microphone Threshold
line
Ku
[
Z
line
MC34216A
line
Vu
Ru
Line AGC
plus an
11
I LAI