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參數(shù)資料
| 型號： | M491B1 |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | SINGLE-CHIP VOLTAGE SYNTHESIS TUNING SYSTEM WITH 1 ANALOG CONTROL |
| 中文描述： | 單片電壓合成調(diào)諧系統(tǒng)的1個(gè)模擬控制 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 135K |
| 代理商： | M491B1 |
SEARCH MODES
4 modesare available:
a) Automaticsearch
b) Automaticpreset
c)
Manualup/down (digital and linear AFT)
d) Manualup/down(linear AFT)
(digiatlAFT)
a) AUTOMATIC SEARCH. The search starts from
the actual tuning and band position. During the
search the tuningvoltage is always changing from
lower to highervoltagelevels. When the end of the
bandis reachedthesearchrestartsfromthebegin-
ning of the next band after a 480 ms interruption
with the sequenceof step-by-stepband selection.
Disabledbands are automaticallyskipped.
The search is stopped when the first station is
found or if a channelselection command is given.
Stop of the automatic searchis determined by the
STOP/AFTinputscontrolledbytheTDA4433which
converts the AFC-S-curve into an up/down com-
mand.
At the end of the search the up/down command
controlsthe correct tuning acting on the counter of
the voltage synthesizer(Digital AFT).
It isimportanttocall theattention totheDigitalAFT
capturerangewhich is largerthanthenormallinear
AFT as shown in fig.14.
LINEAR AFT
CAPTURE RANGE
DIGITAL AFT
CAPTURE RANGE
4
Figure14
Additionallythe use ofthe DigitalAFT allows stor-
age of the tuning informationcorrespondingto the
zero point of the AFC-S-curve. This cannot be
guaranteedusing theLinearAFTmethodonly.The
latter is a cheaper system, because it does not
require the use ofthe TDA4433but it cannotguar-
antee what described above.
As aresultoftheuseoftheDigitalAFT, therequire-
ments for stability of the tuner, of the reference
voltage sourceand of stability of the D/A converter
are less critical.
Tuning speed in automatic search, if no station is
found is :
VHF I
VHF III
UHF
CATV
The tuning and band information can be stored
using the store/memory addressing command.
The searchcan be stoppedby amemory selection
command.
b) AUTOMATIC PRESET. The search starts from
the lowest memory address, tuning voltage and
VHF I band as described in automatic search
mode.
When an active station is encountered,the corre-
sponding tuning and band informationis automat-
ically storedin theNon-Volatile Memory.
Afterwardsthe system starts to search for the next
station. The cycle is repeated untilall bandshave
been scanned or the tuning information has been
stored into all address locations. After completing
thiscycle the systemreads out the tuning informa-
tion of the lowestaddress.
c) MANUAL UP/DOWN WITH DIGITAL AND LIN-
EAR AFT (pin 17 at V
DD
). Holding one of these
commands pressed, the tuning voltage is in-
creased or decreased.
During this operation, the Digital AFT is automat-
ically defeated and can only be reconnected with
the ”AFT on” command or byan Automaticsearch
orpreset command.
The search speed is kept at minimum (there is no
increment with the time)
Sweep Timefor the
Complete Band
VHF I
VHF III
UHF
CATV
seconds
16
In case of command receivedfrom remote control,
the counter is increased/decreased every two re-
ceived commands.
Nobandswitchingis providedatthe upperorlower
tuningpositions.
The volume is automaticallymuted 3 secondafter
the key pressure is immediately restored at the
release of the key.
d)MANUALUP/DOWN WITHLINEARAFT(pin17
at V
SS
). When this control is used the Digital AFT
is disabled.
TheLinearAFToutputgoeslowafteranupordown
command is issued and remains Lowfor 1 second
after the release of the key.
8 second
8 second
32 second
32 second
Band
Number of Tuning
Steps/Second
64
64
16
128 seconds
128 seconds
512 seconds
512
M491B
12/16
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