mc34216adwf Freescale Semiconductor, Inc, mc34216adwf Datasheet - Page 13

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

nominal. When the line current has increased above IL start
with a current IL range , the gain is reduced by 6.0 dB. Due to
the general characteristics of the line AGC curve, the gain will
be decreased further for higher currents.
Region 3 of the dc characteristics. The IL start is approximately
equal to the ILK. The range is determined by:
Loudspeaking Facility
facilitates group listening–in with incorporated anti–howling
circuitry, handsfree conversation with external duplex
controller and ringing via loudspeaker with external switched
mode power supply.
Loudspeaker Amplifier
incorporated in the MC34216A is depicted in Figure 11.
Line +
Line –
Reduced
MOTOROLA ANALOG IC DEVICE DATA
Nominal
For small line currents, and thus long lines, the gains are
For France and the U.K., the line AGC will be active in
For Low Voltage mask, the line AGC is active in Region 2.
The MC34216A incorporates a loudspeaking facility which
The block diagram of the loudspeaker amplifier which is
Gain
Gain
Figure 10. General Line AGC Characteristics
Gain
Z1
IL range
+
HYN
SAI
+
IL
2V
start
R20
Z1 x (I2R – I2CD)
BE + V O1
R1
+
Gain
R
C17
IL
E3
Figure 11. Block Diagram of the Loudspeaker Amplifier
range
+
1
Gnd
Nominal Gain
)
IMP
IL – IL start
Line AGC
IL range
2.4 V
I
RX
I
line
MC34216A
Microphone
Threshold
Anti–
Howl
MC34216A
R
T
Volume
Control
receive part of the earphone amplifier. It therefore also
includes the anti sidetone circuit and the line current AGC.
The overall gain from line to loudspeaker output LPO is
therefore:
the external components as indicated in the formula above.
However, the gain is also influenced by line length AGC,
volume control and the signal limiter AGC.
channel is equal to its influence on the receive amplifier of the
earpiece because it is in their common path.
microcontroller. In total, 8 levels can be programmed: 7 levels
with equal steps of 4.5 dB and one level which completely
mutes the loudspeaker amplifier.
peaks of the signal are larger than a certain threshold (peak
AGC) and when the line current available is not sufficient
(current AGC). This prevents distortion of the output signal
and a drop of the supply voltage V CC .
Listening–In
loudspeaker are active. Via the acoustic coupling from
loudspeaker to handset microphone, howling can occur
when the handset is held close to the base. In order to reduce
howling, an anti–howling correlator and a microphone
threshold are incorporated in the MC34216A. Both functions
can be switched on/off via the microcontroller.
loudspeaker signal via capacitors C26 through C29. When
both signals show a high correlation, then both contain a
common signal. In practice, this means that howling is
present. In this case, the anti–howling correlator will reduce
the loudspeaker gain in steps of 1.25 dB, until the correlation
is below a certain threshold.
A
The first part of the loudspeaker amplifier equals the
The gain of the loudspeaker amplifier can be adjusted by
The influence of line length AGC on the loudspeaker
The volume of the loudspeaker is controlled via the
The output signal is limited by an AGC circuit when the
During group listening–in, both the handset and the
The anti–howling correlator monitors the microphone and
LSP
+
Limiter
Signal
1
+
)
R30
R28
ACG
LPO
LPI
x R
T
x G e x R1 x
C23
C25
R30
R28
C21
C24
Z
1
h
)
Loudspeaker
Z
1
in
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