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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)： | 10/23頁 |
| 文件大?。?/td> | 177K |
| 代理商： | MT8870 |
MSAN-108
Application Note
A-54
"
Twist
"
is known as the difference in amplitude
between the low and high group tones. It is specified
in dB as:
Twist is usually caused by the frequency response
characteristic of the communication channel. Along a
telephone line higher frequencies tend to roll off
faster than the lower ones so the line response is
usually compensated for by applying pre-emphasis
(negative twist) to the originating DTMF signal. In
extreme
cases
the
compensation. This could be realized with a filter
arrangement utilizing the input op amp.
receiver
may
require
Any communication path that can pass the human
voice spectrum is eligible for DTMF signalling.
Therefore a variety of ”front-end“ interfaces may be
applicable in a given control system. More
commonly used media are copper wire and RF
channels. An optical fibre could carry a light beam
modulated by DTMF. Although this would incur a
large overhead in terms of bandwidth utilization,
optical fibres do offer isolation from external electro-
magnetic interference. For example, if control or
data signals must be sent near a high power
transmission line environment, strong electric and
magnetic fields could have a devastating effect on
signals transmitted over wires. DTMF over fibre-
optics could easily be employed as a highly reliable
communications method in a harsh interference
infested environment.
In modern digital switching equipment the MT8870
can easily be interfaced to a digital PCM line by
using a codec as an input interface (Fig. 11).
Actually, all that is required for the interface is a PCM
decoder. In fact, the output filter that normally is
associated with PCM decoders is not required since
the high group DTMF bandpass filter has an upper
cutoff frequency low enough to meet the required
roll-off of the PCM filter.
DTMF In Mobile Radio Applications
DTMF signalling plays an important role in
distributed communications systems, such as multi-
user mobile radio (Fig. 12). It is a
"
natural
"
in the
two-way radio environment since it slips neatly into
the center of the voice spectrum, has excellent noise
immunity
and
highly
implementation are currently available. It is also
directly
compatible
with
simplifying automatic phone patch systems.
integrated
methods
of
telephone
signalling,
Several emergency medical service networks
currently use DTMF signals to control radio
repeaters.
Functions
identification, selection of appropriate repeater links,
selection of repeater frequencies, reading of
repeater status, and for completing automatic phone
patch links.
are,
typically,
mobile
If available in a system of this type, audio from a
long distance communications link (microwave,
TWIST = 20log
10
V
L
V
H
where V
L
is the amplitude of the low frequency tone
and V
H
is the amplitude of the high frequency tone.
Figure 10 - MT8870 Front End Protection Circuit
TIP
RING
ZENERS ARE 15V 250mW
RESISTORS ARE 1% 1/4 W (unless otherwise stated)
0.01
μ
f
110 K
1W
630 V
0.01
μ
f
630 V
110 K
1W
110 K
110 K
52
K
220
K
MT8870
V
Ref
1
2
3
4
68
K
相關(guān)PDF資料 |
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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