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| 型號： | MT8870 |
| 廠商： | Mitel Networks Corporation |
| 英文描述： | () |
| 中文描述： | （） |
| 文件頁數(shù)： | 9/23頁 |
| 文件大?。?/td> | 177K |
| 代理商： | MT8870 |
Application Note
MSAN-108
A-53
attenuation at 685Hz, the required input time
constant may be derived from;
Now, choosing R=220K gives a high input
impedance (440K in the passband) and C=
τ
/R=6.9nF (use a standard value of 10 nF). For
unity gain in the passband we choose R
f
=R. R
a
and
R
b
are biasing resistors. The choice of R
a
is not
critical and could be set at, say... 68K. Bias resistor
R
a
adds a zero to the non-inverting path through the
differential amplifier but has no affect on the inverting
path. This zero can be exactly cancelled by the
added pole due to R
b
if R
b
is chosen as;
With appropriate input transient protection, this
circuit will provide an excellent bridging interface
across a properly terminated telephone line for end-
to-end or key system applications. Transient
protection may be achieved by splitting the input
resistors and inserting zener diodes to achieve
voltage clamping (Fig. 10). This allows the transient
energy to be dissipated in the resistors and diodes
and limits the maximum voltage that may appear at
the op-amp inputs.
It is important to consider the amount of shunt
capacitance introduced by the protection devices. In
this case the parasitic capacitances of the zener
diodes are in series which reduces their effect.
Relatively large shunt capacitances will attenuate the
high group frequencies causing the input signal to
”twist“ which degrades receiver performance.
M
(
ω
)
dB
=20
log
10
+20
log
10
R
f
R
ωτ
{
(
ωτ
)
2
+ 1
}
1/2
where M
(
ω
)
dB
is the amplifier gain in decibels
ω
is the radian frequency
τ
is the input time constant
Therefore
-0.1=20
log
10
(2
π)685τ
{
[
(2
π)685τ]
2
+ 1
}
1/2
or
τ
= 1.52
mS
R
b
=
R
a
R
f
R
a
+
R
f
.
Figure 9 - Differential Input Configuration
AV =
V
o
V
i
R
f
R
S
S + 1/RC
Z(
ω
)
= 2R
1 + (1/
ω
RC)2
1
2
fc =
1
2
π
RC
V
i
R
f
(3)
(2)
(1)
(4)
GS
IN-
IN+
V
Ref
V
o
MT8870
C
R
Voltage Gain;
Input Impedance;
3dB Cutoff Frequency;
C
R
=-
R
b
selection; R
b
=
R
a
R
f
R
a
+ R
f
R
a
R
b
-
+
R
can be chosen to be a
convenient value greater
than 30K
.
+
_
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PDF描述 |
|---|---|
| MT8880C | ISO2-CMOS Integrated DTMFTransceiver |
| MT8880CE-1 | ISO2-CMOS Integrated DTMFTransceiver |
| MT8880CC | ISO2-CMOS Integrated DTMFTransceiver |
| MT8880CE | ISO2-CMOS Integrated DTMFTransceiver |
| MT8880CN | ISO2-CMOS Integrated DTMFTransceiver |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| MT8870BE | 制造商:Panasonic Industrial Company 功能描述:RECEIVER |
| MT8870D | 制造商:MITEL 制造商全稱:Mitel Networks Corporation 功能描述:ISO2-CMOS Integrated DTMF Receiver |
| MT8870DC | 制造商:MITEL 制造商全稱:Mitel Networks Corporation 功能描述:ISO2-CMOS Integrated DTMF Receiver |
| MT8870DC-1 | 制造商:MITEL 制造商全稱:Mitel Networks Corporation 功能描述:ISO2-CMOS Integrated DTMF Receiver |
| MT8870DE | 制造商:Microsemi Corporation 功能描述: |
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