IL34118N View Datasheet(PDF) - IK Semicon Co., Ltd
Part Name
Description
MFG CO.
IL34118N Datasheet PDF : 14 Pages
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IL34118
ATTENUATOR CONTROL BLOCK
The Attenuator Control Block has the seven inputs
described above:
- The output of the comparator operated by RLO2 and
TLO2 (microphone/speaker side) - designated C1.
- The output of the comparator operated by RLO1 and
TLO1 (Tip/Ring) side) - designated C2.
- The output of the transmit background noise
monitor - designated C3.
- The output of the receive background noise
monitor - designated C4.
- The volume control.
- The dial tone detector.
- The AGC circuit.
The single output of the Control Block controls the
two attenuators. The effect of C1-C4 is as follows:
Inputs
Output
C1
C2
C3
C4
Mode
Tx
Tx
1
X
Transmit
Tx
Rx
Y
Y
Fast Idle
Rx
Tx
Y
Y
Fast Idle
Rx
Rx
X
1
Receive
Tx
Tx
0
X
Slow Idle
Tx
Rx
0
0
Slow Idle
Rx
Tx
0
0
Slow Idle
Rx
Rx
X
0
Slow Idle
X = Don’t Care; Y = C3 and C4 are not both 0
A definition of the above terms:
1) “Transmit” means the transmit attenuator is fully on
(+6.0 dB), and the receive attenuator is at max.
attenuation (-46 dB).
2) “Receive” means both attenuators are controlled by
the volume control. At max. volume, the receive
attenuator is fully on (6.0 dB), and the transmit
attenuator is at max. attenuation (-46 dB).
3) “Fast Idle” means both transmit and receive speech
are present in approximately equal levels. The
attenuators are quickly switched (30 ms) to idle
until one speech level dominates the other.
4) “Slow Idle” means speech has ceased in both
transmit and receive path. The attenuators are then
slowly switched (1 second) to the idle mode.
5) Switching to the full transmit or receive modes
from any other mode is at the fast rate (30 ms).
A summary of the truth table is as follows:
1) The circuit will switch to transmit if: a) both
transmit level detectors sense higher signal levels
relative to the respective receive level detectors (TLI1
versus RLI1, TLI2 versus RLI2), and b) the transmit
background noise monitor indicates the presence of
speech.
2) The circuit will switch to receive if: a) both receive
level detectors sense higher signal levels relative to the
respective transmit level detectors, and b) the receive
background noise monitor indicates the presence of
speech.
3) The circuit will switch to the fast idle mode if the
level detectors disagree on the relative strengths of the
signal levels, and at least one of the background noise
monitors indicates speech. For example, referring to the
Expanded Logic Diagram (Figure 8), if there is sufficient
signal at the microphone amp output (TLI2) to override
the speaker signal (RLI2), and there is sufficient signal at
the receive input (RLI1) to override the signal at the
hybrid output (TLI1), and either or both background
monitors indicate speech, then the circuit will be in the
fast idle mode. Two conditions which can cause the fast
idle mode to occur are a) when both talkers are
attempting to gain control of the system by talking at the
same time, and b) when one talker is in a very noisy
environment, forcing the other talker to continually
override that noise level. In general, the fast idle mode
will occur infrequently.
4) The circuit will switch to the slow idle mode when
a) both talkers are quiet (no speech present), or b) when
one talker’s speech level is continuously overriden by
noise at the other speaker’s location.
The time required to switch the circuit between
transmit, receive, fast idle and slow idle is determined in
part by the components at the CT pin (Pin 14). A
schematic of the CT circuitry is shown in Figure 4 and
operates as follows:
- RT is typically 120 k, and CT typically 5.0 F.
- To switch to the receive mode, I1 is turned on (I2 is
off), charging the external capacitor to +240 mV
above VB. (An internal clamp prevents further
charging of the capacitor.)
- To switch to the transmit mode, I2 is turned on (I1 is
off) bringing down the voltage on the capacitor to -
240 mV with respect to VB.
- To switch to idle quickly (fast idle), the current
sources are turned off, and the internal 2.0 k
resistor is switched in, discharging the capacitor to
VB with a time constant = 2.0 K x CT.
- To switch to idle slowly (slow idle), the current
sources are turned off, the switch at the 2.0 k
resistor is open, and the capacitor discharges to VB
through the external resistor RT with a time constant
= RT x CT.
2013, January, Ver. 02
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