欢迎访问ic37.com |
会员登录 免费注册
发布采购

MT8870DSR 参数 Datasheet PDF下载

MT8870DSR图片预览
型号: MT8870DSR
PDF下载: 下载PDF文件 查看货源
内容描述: [DTMF Signaling Circuit, CMOS, PDSO18, 0.300 INCH, MS-013AB, SOIC-18]
分类和应用: 光电二极管
文件页数/大小: 29 页 / 626 K
品牌: ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
 浏览型号MT8870DSR的Datasheet PDF文件第1页浏览型号MT8870DSR的Datasheet PDF文件第2页浏览型号MT8870DSR的Datasheet PDF文件第4页浏览型号MT8870DSR的Datasheet PDF文件第5页浏览型号MT8870DSR的Datasheet PDF文件第6页浏览型号MT8870DSR的Datasheet PDF文件第7页浏览型号MT8870DSR的Datasheet PDF文件第8页浏览型号MT8870DSR的Datasheet PDF文件第9页  
ISO2-CMOS MT8870D/MT8870D-1  
Functional Description  
V
DD  
The  
MT8870D/MT8870D-1  
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 a digital counting  
section which verifies the frequency and duration of  
the received tones before passing the corresponding  
code to the output bus.  
C
V
DD  
St/GT  
ESt  
v
c
R
StD  
Filter Section  
MT8870D/  
MT8870D-1  
t
t
=(RC)In(V /V  
)
GTA  
GTP  
DD TSt  
=(RC)In[V /(V -V )]  
DD  
DD TSt  
Separation of the low-group and high group tones is  
achieved by applying the DTMF signal to the inputs  
of two sixth-order switched capacitor bandpass  
filters, 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 Figure 3). Each  
filter output is followed by a single order switched  
capacitor filter section which smooths 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.  
Figure 4 - Basic Steering Circuit  
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 frequencies (third tones) and noise. When  
the detector recognizes the presence of two valid  
tones (this is referred to as the “signal condition” in  
some industry specifications) the “Early Steering”  
(ESt) output will go to an active state. Any  
subsequent loss of signal condition will cause ESt to  
assume an inactive state (see “Steering Circuit”).  
Decoder Section  
Steering Circuit  
Following the filter section is a decoder employing  
digital counting techniques to determine the  
frequencies of the incoming 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  
Before registration of a decoded tone pair, the  
receiver checks for a valid signal duration (referred to  
as character recognition condition). This check is  
performed by an external RC time constant driven by  
ESt. A logic high on ESt causes v (see Figure 4) to  
c
rise as the capacitor discharges. Provided signal  
0
PRECISE  
DIAL TONES  
X=350 Hz  
Y=440 Hz  
10  
DTMF TONES  
20  
A=697 Hz  
B=770 Hz  
C=852 Hz  
D=941 Hz  
E=1209 Hz  
F=1336 Hz  
G=1477 Hz  
H=1633 Hz  
ATTENUATION  
(dB)  
30  
40  
50  
1kHz  
X
Y
A B  
C
D
E
F
G
H
FREQUENCY (Hz)  
Figure 3 - Filter Response  
4-13