參數(shù)資料
型號(hào)： U4084B
英文描述： Low-Voltage, Voice-Switched Circuit for Hands-Free Operation
中文描述： 低電壓，語(yǔ)音開(kāi)關(guān)電路免提操作
文件頁(yè)數(shù)： 14/26頁(yè)
文件大?。?/td> 544K
代理商： U4084B
U4084B
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
Preliminary Information
14 (26)
When activated, the muting function (Pin 9) reduces the
gain of the amplifier to approximately – 39 dB (with RMI
= 5.1 k ) by shorting the output to the inverting input (see
figure 7). The mute input has a threshold of
approximately 1.5 V, and the voltage at this pin must be
kept within the range of ground and V
S
(see figure 15). If
the mute function is not used, the pin should be grounded.
Power Supply, V
B
, and Chip Disable
The power supply voltage at Pin 4 (V
S
) is between 3.5 and
6.5 V for normal operation. Reduced operation at 2.8 V
is, however, also possible (see figure 13 and the AGC
section). The power supply current is shown in figure 16
for both operations, power-up and power-down mode.
The output voltage at V
B
(Pin 12) is approximately
(V
S
–0.7)/2. and provides the AC ground for the system.
The output impedance at V
B
is approximately 400 (see
figure 17), and forms
together with the external capaci-
tor at V
B
a low-pass filter for power supply rejection.
Figure 18 indicates the amount of rejection for different
capacitors. The capacitor values depend on whether the
circuit is powered by the telephone line or a power supply.
Since V
B
biases the microphone amplifier, the amount of
supply rejection at its output is directly related to the
rejection at V
B
, as well as its gain. Figure 19 depicts this
graphically.
The chip disable (Pin 3) permits powering down the IC to
conserve power and/or for muting purposes. With CD
< 0.8 V, normal operation is in effect.
With CD > 2.0 V and < V
S
, the IC is powered down. In
the power-down mode, the microphone amplifier is
disabled, and its output goes to a high impedance state.
Additionally, the bias is removed from the level detectors.
The bias is not removed from the attenuators (Pins 5, 6,
18 and 19), or from Pins 10, 11 and 12 (the attenuators are
disabled, however, and will not pass a signal). The input
impedance at CD is typically 90 k and has a threshold
of approximately 1.5 V. The voltage at this pin must be
kept within the range of ground and V
S
(see figure 15). If
CD is not used, the pin should be grounded.
– 160
0
160
0
– 40
– 50
– 30
– 10
– 20
T attenuator
R attenuator
V
CT
– V
B
(mV)
G
10
320
– 320
93 7767 e
Figure 8. Attenuator gain versus VCT (Pin 11)
– 20
100
200
400
– 80
– 40
– 60
300
0
(
O
V
I
I
( A)
0
– 100
500
93 7768 e
Figure 9. Level-detector DC transfer characteristics
R = 5.1 k
C = 0.1 F
↓
R = 10 k
C = 0.047 F or 0.1 F
V
i
(mVrms)
20
80
150
200
4
250
50
100
60
0
(
O
V
0
100
300
93 7769 e
←
f = 1 kHz
Figure 10. Level-detector AC transfer characteristics
相關(guān)PDF資料
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