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參數(shù)資料
| 型號： | U4084B |
| 英文描述： | Low-Voltage, Voice-Switched Circuit for Hands-Free Operation |
| 中文描述： | 低電壓，語音開關(guān)電路免提操作 |
| 文件頁數(shù)： | 19/26頁 |
| 文件大小： | 544K |
| 代理商： | U4084B |
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U4084B
Preliminary Information
TELEFUNKEN Semiconductors
Rev. A1, 31-Jan-97
19 (26)
I)
The total loop gain (of figure 21) must add up to a value
< 0 dB to obtain a stable circuit. This can be expressed as:
Loop Gain
G
MA
+ G
T
+ G
EXT
+ G
ST
+ G
EXR
+ G
R
+ G
SA
+ G
AC
< 0
. . . . . . 1
Using the typical numbers mentioned above, and using
the equation G
T
+ G
R
= –40dB, the required acoustic cou-
pling can be determined:
G
AC
<–
[
31 + 20.1 + (–15) + 0 + (–40) + 26.8
]
+ –22.9
. . . . . . 2
An acoustic loss of at least 23 dB is necessary to prevent
instability and oscillations, commonly referred to as
“singing”. However, the following equations show that
greater values of acoustic loss are necessary to obtain
proper level detection and switching.
II)
Switching Thresholds
To switch comparator C1, the currents I
1
and I
3
have to
be determined. When a receive signal V
L
is applied to
Tip/Ring, a current I
3
flows through R3 into RLI2 (see
figure 21) according to the following equation:
I
3
V
L
R
3
G
EXR
G
R
G
SA
2
. . . . . . 3
where the terms in the brackets are in V/V gain terms. The
speaker amplifier gain is divided by two since G
SA
is the
differential gain of the amplifier, and V
3
is obtained from
one side of that output. The current I
1
, coming from the
microphone circuit, is defined by:
I
1
V
M
G
MA
R
1
. . . . . . 4
where V
M
is the microphone voltage. Since the switching
threshold occurs when I
1
= I
3
, combining the above two
equations yields:
V
M
V
L
R
1
R
3
[G
EXR
G
R
G
SA
]
G
MA
2
. . . 5
This is the general equation defining the microphone volt-
age necessary to switch comparator C1 when a receive
signal V
L
is present. The highest V
M
occurs when the
receive attenuator is at maximum gain (+ 6.0 dB). Using
the typical values of equation 5 results in:
V
M
= 0.52 V
L
. . . . . . 6
To switch comparator C2, the currents I
2
and I
4
need to
be determined. When sound is applied to the microphone,
a voltage V
M
is created by the microphone, resulting in
a current I
2
into TLI1:
I
2
V
M
R
2
G
MA
G
T
G
EXT
2
. . . . . . 7
Since G
EXT
is the differential gain of the external transmit
amplifiers, it is divided by two to obtain the voltage V
2
applied to R
2
. Comparator C2 switches when I
4
= I
2
. I
4
is
defined by:
I
4
V
L
R
4
[G
EXR
]
. . . . . . 8
Setting I
4
= I
2
, and combining the above equations results
in:
V
L
V
M
R
4
R
2
[G
MA
G
T
G
EXT
]
G
EXR
2
. . . 9
This equation defines the line voltage at Tip/Ring neces-
sary to switch comparator C2 in the presence of a
microphone voltage. The highest V
L
occurs when the
circuit is in transmit mode (G
T
= + 6.0 dB). Using the
typical values for equation 9 yields:
V
L
= 840 V
M
(or V
M
= 0.0019 V
L
) . . . . . . 10
At idle mode, where the gain of the two attenuators is –20
dB (0.1 V/V), equations 6 and 10 yield the same result:
V
M
= 0.024 V
L
. . . . . . 11
Equations 6, 10, and 11 define the thresholds for switch-
ing, and are represented in figure 22.
The “M” terms are the slopes of the lines (0.52, 0.024, and
0.0019) which are the coefficients of the three equations.
The M
R
line represents the receive to transmit threshold
in that it defines the microphone signal level necessary to
switch to transmit in the presence of a given receive signal
level. The M
T
line represents the transmit to receive
threshold. The M
I
line represents the idle condition, and
defines the threshold level on one side (transmit or
receive) necessary to overcome noise on the other.
V
M
V
L
M
I
M
T
M
R
12678
Figure 22. Switching thresholds
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| U4087B | Low Voltage Voice Switch Interface Circuit for Hands-free Operation in Telephone |
| U4087B-FP | Low Voltage Voice Switch Interface Circuit for Hands-free Operation in Telephone |
| U4090B-N | Low power dual voltage comparators |
| U4090B-NFN | Low power dual voltage comparators |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| U4084B-FL | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Speakerphone Circuit |
| U4085B | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Technische Daten Technical Data |
| U4087B | 制造商:TEMIC 制造商全稱:TEMIC Semiconductors 功能描述:Low Voltage Voice Switch Interface Circuit for Hands-free Operation in Telephone |
| U4087B-FP | 制造商:TEMIC 制造商全稱:TEMIC Semiconductors 功能描述:Low Voltage Voice Switch Interface Circuit for Hands-free Operation in Telephone |
| U4089B | 制造商:ATMEL 制造商全稱:ATMEL Corporation 功能描述:MONOLITHIC INTEGRATED FEATUREPHONE CIRCUIT |
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