U4084B TEMIC [TEMIC Semiconductors], U4084B Datasheet - Page 13

• Manufacturer Part Number: U4084B
• Description: Low-Voltage, Voice-Switched Circuit for Hands-Free Operation
• Manufacturer: TEMIC [TEMIC Semiconductors]

TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Operation of the C
–
–
–
–
–
R
To switch to receive mode, I
off), charging the external capacitor to + 240 mV
above V
charging of the capacitor).
To switch to transmit mode, I
off) bringing down the voltage on the capacitor
to – 240 mV with respect to V
To switch to idle mode quickly (fast idle), the
current sources are turned off, and the internal
2.0-k
capacitor to V
C
To switch to idle slowly (slow idle), the current
sources are turned off, the switch at the 2.0-k
resistor is open, and the capacitor discharges to
V
T
T
B
.
is typ. 120 k
with a time constant = R
W
resistor is switched on, discharging the
B.
(An internal clamp prevents further
B
W
with a time constant = 2.0 k
C
V
R
C
and C
T
T
B
T
T
Circuitry
12
11
I
1
T
is typ. 5.0
T
Preliminary Information
1
2
Figure 6. C
B
is turned on (I
2k
I
is turned on (I
.
2
C
A
T
.
m
F.
T
attenuator control block circuit
W
2
1
W
is
is
Attenuator
control
Microphone Amplifier, Pins 7, 8 and 9
The non-inverting input of the microphone amplifier
(Pins 7 and 8) is connected to V
put and the output are pinned out.
Unlike most op amps, the amplifier has an all NPN output
stage which maximizes phase margin and gain band-
width. This feature ensures stability at gains less than
unity, as well with a wide range of reactive loads.
The open loop gain is typically 80 dB (f < 100 Hz), and
the gain-bandwidth is typ. 1.0 MHz (see figure 4). The
maximum p-p output swing is typ. (V
put impedance of < 10
(typ. 1.5 mA). The input bias current at MIC is typically
– 40 nA.
Mike
from
+
–
R
R
MI
MF
Figure 7. Microphone amplifier and mute
MUTE
MIC
4
to attenuators
Volume control
Dial-tone detector
AGC
8
9
C1 ... C4
V
W
S
90k
until current limiting is reached
B
75k
V
, while the inverting in-
B
U4084B
S
+
12675
–
– 1 V) with an out-
V
S
12676
7
13 (26)
MICO