TS34118CS28C8 TSC [Taiwan Semiconductor Company, Ltd], TS34118CS28C8 Datasheet - Page 10

• Manufacturer Part Number: TS34118CS28C8
• Description: Voice Switched Speakerphone Circuit
• Manufacturer: TSC [Taiwan Semiconductor Company, Ltd]

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:
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 (+6.0dB), and the receive attenuator is at max. attenuation
2) ”Receive” means both attenuators are controlled by the volume control. At max. Volume, the receive attenuator is
3) ”Fast Idle” means both transmit and receive speech is present in approximately equal levels. The attenuators are
4) ”Slow Idle” means speech has ceased in both transmit and receive paths. The attenuators are then slowly switched
5) Switch to the full transmit or receive modes from any other mode is at the fast rate (≈30ms).
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
2) The circuit will switch to receive if: a) both receive level detectors sense higher signal levels relative to the
3) The circuit will switch to the fast idle mode if the level detectors disagree on the relative strengths of the signal levels,
(- 46dB).
fully on (+6.0dB), and the transmit attenuator is at max. attenuation (-46dB).
quickly switched (30ms) to idle until one speech level dominates the other.
(1 second) to the idle mode.
respective receive level detectors (TLI1 versus RLI1, TLI2 versus RLI2), and b) the transmit background noise
monitor indicates the presence of speech.
respective transmit level detectors, and b) the receive background noise monitor indicates the presence of speech.
and at least one of the background noise monitors indicates speech. For example, referring to the Block Diagram
(Figure 2), 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.
C1
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
C2
Rx
Rx
Rx
Rx
Tx
Tx
Tx
Tx
Input
C3
Y
Y
X
X
1
0
0
0
C4
X
Y
X
1
0
0
0
y
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Slow Idle
Slow Idle
Slow Idle
Slow Idle
Transmit
Fast Idle
Fast Idle
Receive
Output
Voice Switched Speakerphone Circuit
Mode
TS34118
Version: A08