TS34118

18-20

2004/09 rev. B

Application Information

Dial Tone Detector

be reduced by connecting a resistor from RXI to ground. The resistor value is calculated from:

R =

⎥⎦

⎤

⎢⎣

⎡

−1

∆V

V

10K

B

RXI, the threshold can be increased. The resistor value is calculated from:

R =

⎥⎦

⎤

⎢⎣

⎡

−

−

1

∆V

V

V

10K

B

CC

Where ∆V 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.

value is calculated from:

R =

⎥⎦

⎤

⎢⎣

⎡

−1

∆V

VB

R

T

is calculated from:

R =

⎥⎦

⎤

⎢⎣

⎡

−

−

1

∆V

V

V

R

B

CC

T

voltage excursions required to get to transmit and receive from idle. For practical considerations, the ∆V shift should not

exceed 100mV.