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參數(shù)資料
| 型號： | MS8870 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | DTMF Receiver |
| 中文描述： | 雙音多頻接收器 |
| 文件頁數(shù)： | 6/8頁 |
| 文件大?。?/td> | 138K |
| 代理商： | MS8870 |
MOSA ELECTRONICS
MS8870
DTMF Receiver
－
6
－
Functional Description
The MS8870 monolithic DTMF receiver offers small
size, low power consumption and high performance. Its
architecture consists of a bandsplit filter section, which
separates the high and low group tones, followed by digital
counting section which verifies the frequency and duration
of the received tones before passing the corresponding
code to the output bus.
Filter Section
Separation of the low-group and high-group tones is
achieved by applying the DTMF signal to the inputs of two
filters
－
a sixth order for the high group and an eighth
order for the low group. The bandwidths of which
correspond to the low and high group frequencies. The
filter section also incorporates notches at 350 and 440 Hz
for exceptional dial tone rejection (see Fig. 4). Each filter
output is followed by a single order switched capacitor
filter section which smoothes the signals prior to limiting.
Limiting is performed by high-gain comparators which are
provided with hysteresis to prevent detection of unwanted
low-level signals. The outputs of the comparators provide
full rail logic swings at the frequencies of the incoming
DTMF signals.
Decoder Section
The decoder uses digital counting techniques to
determine the frequencies of limited tones and to verify
that they correspond to standard DTMF frequencies. A
complex averaging algorithm protects against tone
simulation by extraneous signals, such as voice, while
providing tolerance to small frequency deviations and
variations. This averaging algorithm has been developed to
ensure an optimum combination of immunity to "talk-off"
and tolerance to the presence of interfering signals ("third
tones") and noise. When the detector recognizes the
simultaneous presence of two valid tone (referred to as
"signal condition" in some industry specifications), it
raises the "early steering" flag (ESt). Any subsequent loss
of signal-condition will cause ESt to fall.
F
LOW
F
HIGH
NO
TOE
Q4
Q3
Q2
Q1
697 1209
1
H
0
0
0
1
697 1336
2
H
0
0
1
0
697 1477
3
H
0
0
1
1
770 1209
4
H
0
1
0
0
770 1336
5
H
0
1
0
1
770 1477
6
H
0
1
1
0
852 1209
7
H
0
1
1
1
852 1336
8
H
1
0
0
0
852 1477
9
H
1
0
0
1
941 1336
0
H
1
0
1
0
941 1209
*
H
1
0
1
1
941 1477
#
H
1
1
0
0
697 1633
A
H
1
1
0
1
770 1633
B
H
1
1
1
0
Figure 4. 6TH Order Bandpass
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