Electronic Components Datasheet Search
Selected language     English  ▼
Part Name
         Description


M-8870-01SM Datasheet(PDF) 3 Page - Clare, Inc.

Part No. M-8870-01SM
Description  DTMF Receiver
Download  9 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  CLARE [Clare, Inc.]
Homepage  http://www.clare.com
Logo 

   
 3 page
background image
M-8870
www.clare.com
3
Rev. 3
Basic Steering Circuit
Single-Ended Input Configuration
Functional Description
M-8870 operating functions (see block diagram on
page 1) include a bandsplit filter that separates the
high and low tones of the received pair, and a digital
decoder that verifies both the frequency and duration
of the received tones before passing the resulting 4-bit
code to the output bus.
Filter
The low and high group tones are separated by apply-
ing the dual-tone signal to the inputs of two 6th order
switched capacitor bandpass filters with bandwidths
that correspond to the bands enclosing the low and
high group tones. The filter also incorporates notches
at 350 and 440 Hz, providing excellent dial tone rejec-
tion. Each filter output is followed by a single-order
switched capacitor section that smooths the signals
prior to limiting. Signal limiting is performed by high-
gain comparators provided with hysteresis to prevent
detection of unwanted low-level signals and noise.
The comparator outputs provide full-rail logic swings
at the frequencies of the incoming tones.
Decoder
The M-8870 decoder uses a digital counting tech-
nique to determine the frequencies of the limited tones
and to verify that they correspond to standard DTMF
frequencies. A complex averaging algorithm is used to
protect against tone simulation by extraneous signals
(such as voice) while tolerating small frequency varia-
tions. The algorithm ensures an optimum combination
of immunity to talkoff and tolerance to interfering sig-
nals (third tones) and noise. When the detector rec-
ognizes the simultaneous presence of two valid tones
(known as signal condition), it raises the Early
Steering flag (ESt). Any subsequent loss of signal
condition will cause ESt to fall.
Steering Circuit
Before a decoded tone pair is registered, the receiver
checks for a valid signal duration (referred to as char-
acter-recognition-condition). This check is performed
by an external RC time constant driven by ESt. A logic
high on ESt causes VC (see block diagram on page 1)
to rise as the capacitor discharges. Provided that sig-
nal condition is maintained (ESt remains high) for the
validation period (t
GTF), VC reaches the threshold (VTSt)
of the steering logic to register the tone pair, thus latch-
ing
its
corresponding
4-bit
code
(see
DC
Characteristics on page 2) into the output latch. At this
point, the GT output is activated and drives V
C to VDD.
GT continues to drive high as long as ESt remains
high. Finally, after a short delay to allow the output
latch to settle, the delayed steering output flag (StD)
goes high, signaling that a received tone pair has been
registered. The contents of the output latch are made
available on the 4-bit output bus by raising the three-
state control input (OE) to a logic high. The steering
circuit works in reverse to validate the interdigit pause
between signals. Thus, as well as rejecting signals too
short to be considered valid, the receiver will tolerate
signal interruptions (dropouts) too short to be consid-
ered a valid pause. This capability, together with the
ability to select the steering time constants externally,
allows the designer to tailor performance to meet a
wide variety of system requirements.




Html Pages

1  2  3  4  5  6  7  8  9 


Datasheet Download



Related Electronics Part Number

Part NumberComponents DescriptionHtml ViewManufacturer
BU8871FDTMF receiver for telephones 1 2 3 4 5 MoreRohm
IN9270DTMF RECEIVER High-Performance Silicon-Gate CMOS 1 2 3 4 5 MoreIntegral Corp.
BU8872DTMF receiver for telephones 1 2 3 4 5 MoreRohm
LC7385DTMF Receiver 1 2 3 4 5 MoreSanyo Semicon Device
CD222025V Low Power DTMF Receiver 1 2 3 4 5 MoreIntersil Corporation
IL9270NDTMF signal receiver 1 2 3 4 5 List of Unclassifed Manufacturers
HT9172DTMF Receiver 1 2 3 4 5 MoreHoltek Semiconductor Inc
BU8874DTMF receiver for telephones 1 2 3 4 5 MoreRohm
LC73860DTMF Receiver IC 1 2 3 4 5 MoreSanyo Semicon Device
CD222045V Low Power Subscriber DTMF Receiver 1 2 3 4 5 Intersil Corporation

Link URL

Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Datasheet Upload   |   Contact us   |   Privacy Policy   |   Bookmark   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com 2003 - 2017    


Mirror Sites
English : Alldatasheet.com  , Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp  |   Russian : Alldatasheetru.com
Korean : Alldatasheet.co.kr   |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com  |   Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl