U4082B Datasheet, PDF (28/30 Pages) ATMEL Corporation – Low-voltage Voice-switched IC for Hands-free Operation

9.3 Transmit/Receive Detection Priority
Although the U4082B was designed to have idle mode such that the attenuators are halfway
between their full on and full off positions, 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_T (pin 14) to ground, the circuit will be biased towards the trans-
mit side. The resistor value is calculated from:
R = R_T
-V----^B--
∆V
–
1
where
R_T = 120 kΩ (typ.) connected between pin 14 and 15.
∆V= V_B – V14 (see Figure 7-1 on page 17).
By connecting a resistor from C_T (pin 14) to V_S, the circuit will be biased towards the receive
side. The resistor value is calculated from:
R = R_T
-V----^S----^–-----V----^B--
∆V
–
1
Switching time will be somewhat affected in each case due to the different voltage excursions
required to get to transmit and receive from idle. For practical considerations, the ∆V shift should
not exceed 100 mV.
28 U4082B
4743D–CORD–03/06