U4082B-DEV-BOARD Atmel, U4082B-DEV-BOARD Datasheet - Page 10

• Manufacturer Part Number: U4082B-DEV-BOARD
• Description: WiFi / 802.11 Modules & Development Tools Voice Switched Circuit
• Manufacturer: Atmel

3.11
10
Microphone Amplifier
U4082B
The microphone amplifier (pins 10, 11) has the non-inverting input internally connected to V
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
an output impedance of < 10 until current limiting is reached (typically 1.5 mA). Input bias cur-
rent at MIC is typically –40 nA.
Figure 3-5.
Figure 7-7 on page
– R
– To switch to receive mode, I
– To switch to transmit mode, I
– To switch to idle mode quickly (fast idle), the current sources are turned off, and the
– To switch to idle mode slowly (slow idle), the current sources are turned off, the
+240 mV above V
capacitor to –240 mV with respect to V
internal 2 k resistor is switched on, discharging the capacitor to V
constant of 2 k
switch at the 2 k resistor is open, and the capacitor discharges to V
external resistor, R
T
is typically 120 k , and C
Microphone Amplifier and Mute
From
microphone
19). The maximum peak-to-peak output swing is typically (V
B
T
. (An internal clamp prevents further charging of the capacitor.)
C
, with a time constant of = R
T
R
.
R
MI
MF
MUTE
MIC
1
12
2
11
T
is turned on (I
is turned on (I
is typically 5.0 µF.
V
90 k
S
B
.
2
V
1
75 k
is off), charging the external capacitor to
B
is off), bringing down the voltage on the
T
+
-
C
V
T
.
S
10
MICO
B
with a time
B
through the
4743D–CORD–03/06
S
– 1V) with
B
,