ts34118 Taiwan Semiconductor Company, Ltd. (TSC), ts34118 Datasheet - Page 18

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

TS34118
Application Information
Dial Tone Detector
The threshold for the dial tone detector is internally set at 15mV (10mVrms) below V
be reduced by connecting a resistor from RXI to ground. The resistor value is calculated from:
Where V
RXI, the threshold can be increased. The resistor value is calculated from:
Where ûV is the amount of threshold increase.
Background Noise Monitors
For testing or circuit analysis purposes, the transmit or receive attenuators can be set to the “on” position, by disabling
the background noise monitors, and applying a signal so as to activate the level detectors. Grounding the CPR pin will
disable the receive background noise monitor, thereby indicating the “presence of speech” to the attenuator control
block. Grounding CPT does the same for the transmit path.
Additionally, the receive background noise monitor is automatically disabled by the dial tone detector whenever the
receive signal exceeds the detector’s threshold.
Transmit / Receive Detection Priority
Although the TS34118 was designed to have an idle mode such that the attenuators are halfway between their full on
and full off positions, the idle mode can be biased towards the transmit or the receive side. With this done, gaining
control of the circuit from idle will be easier for that side towards which it is biased since that path will have less
attenuation at idle.
By connecting a resistor from C
value is calculated from:
Where R is the added resistor, R
difference between V
By connecting a resistor from C
is calculated from:
R, R
voltage excursions required to get to transmit and receive from idle. For practical considerations, the ûV shift should not
exceed 100mV.
T
, and ûV are the same as above. Switching time will be somewhat affected in each case due to the different
R =
R =
R =
R =
B
is the voltage at Pin 15, and ûV is the amount of threshold reduction. By connecting a resistor from Vcc to
10K
10K
R
R
T
T
ª
« ¬
ª
« ¬
ª
« ¬
ª
« ¬
VB
ûV
V
ûV
V
V
CC
CC
ûV
B
B
ûV
 1

and the voltage at C7 at idle C refer to (Figure 10)
 1

V
º
» ¼
V
º
» ¼
B
B


1
T
1
º
» ¼
T
º
» ¼
(pin 14) to Vcc, the circuit will be biased towards the transmit side. The resistor value
(pin 14) to ground, the circuit will be biased towards the transmit side. The resistor
T
is the resistor normally between pins 14 and 15 (typically 120 ), and ûV is the
18-20
B
(see Figure 5). That threshold can
2004/09 rev. B