U4082B Datasheet, PDF (10/30 Pages) ATMEL Corporation – Low-voltage Voice-switched IC for Hands-free Operation

– R_T is typically 120 kΩ, and C_T is typically 5.0 µF.
– To switch to receive mode, I₁ is turned on (I₂ is off), charging the external capacitor to
+240 mV above V_B. (An internal clamp prevents further charging of the capacitor.)
– To switch to transmit mode, I₂ is turned on (I₁ is off), bringing down the voltage on the
capacitor to –240 mV with respect to V_B.
– To switch to idle mode quickly (fast idle), the current sources are turned off, and the
internal 2 kΩ resistor is switched on, discharging the capacitor to V_B with a time
constant of 2 kΩ × C_T.
– To switch to idle mode slowly (slow idle), the current sources are turned off, the
switch at the 2 kΩ resistor is open, and the capacitor discharges to V_B through the
external resistor, R_T, with a time constant of = R_T × C_T.
3.11
Microphone Amplifier
The microphone amplifier (pins 10, 11) has the non-inverting input internally connected to V_B,
while the inverting input and the output are pinned out.
Unlike most operational amplifiers, this amplifier has an all-NPN output stage which maximizes
phase margin and gain bandwidth. This feature ensures stability at gains less than unity, as well
as with a wide range of reactive loads.
The open loop gain is typically 80 dB (f < 100 Hz), and the gain-bandwidth is typically 1.0 MHz
(see Figure 7-7 on page 19). The maximum peak-to-peak output swing is typically (V_S – 1V) with
an output impedance of < 10Ω until current limiting is reached (typically 1.5 mA). Input bias cur-
rent at MIC is typically –40 nA.
Figure 3-5. Microphone Amplifier and Mute
R_MF
R_MI
11
From
MIC
microphone
12
MUTE
V_S
V_B ⁺
-
V_S
90 kΩ
10
MICO
75 kΩ
10 U4082B
4743D–CORD–03/06