ts34118 Taiwan Semiconductor Company, Ltd. (TSC), ts34118 Datasheet - Page 10

• Manufacturer Part Number: ts34118
• Description: Voice Switched Speakerphone Circuit
• Manufacturer: Taiwan Semiconductor Company, Ltd. (TSC)

TS34118
Attenuator Control Block
The Attenuator Control Block has the seven inputs described above:
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:
A summary of the truth table is as follows:
-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.
5) Switch to the full transmit or receive modes from any other mode is at the fast rate (§30ms).
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 fully
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 (1
1)The circuit will switch to transmit if: a) both transmit level detectors sense higher signal levels relative to the respective
2)The circuit will switch to receive if: a) both receive level detectors sense higher signal levels relative to the respective
3) The circuit will switch to the fast idle mode if the level detectors disagree on the relative strengths of the signal
receive level detectors (TLI1 versus RLI1, TLI2 versus RLI2), and b) the transmit background noise monitor indicates
the presence of speech.
transmit level detectors, and b) the receive background noise monitor indicates the presence of speech.
levels, 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.
(-46dB).
on (+6.0dB), and the transmit attenuator is at max. attenuation (-46dB).
quickly switched (30ms) to idle until one speech level dominates the other.
second) to the idle mode.
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
10-20
C4
X
Y
X
y
1
0
0
0
Slow Idle
Slow Idle
Slow Idle
Slow Idle
Transmit
Fast Idle
Fast Idle
Receive
Output
Mode
2004/09 rev. B