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參數(shù)資料
| 型號： | M491B1 |
| 廠商： | 意法半導體 |
| 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個模擬控制 |
| 文件頁數(shù)： | 9/16頁 |
| 文件大?。?/td> | 135K |
| 代理商： | M491B1 |
M491B Pin 12
TDA4433 Pin 2
H
L
L
H
M491 B Pin 13
TDA4433 Pin 6
L
H
L
H
Function
(referred to the tuning voltage)
Up
Down
Middle
No Operation
4
Thesepins workaccordingto the truth table given below :
These inputs have two different functions depend-
ing on whether the system is in the search or in
normal operation(AFT control).
The inputs have internal pull-up resistors of 30k
typ.
A)
Searchmode :
afterdepressingthe Automatic
search or presetkeys, thelevels of the signals
coming from the TDA4433, applied to these
pins, controlthe searchfunctionanddetermine
when thesearchmuststop,i.e.aTVstationhas
been recognized.
The circuit operates in the following sequence
(see Figure 10 for reference):
1 - after pressing the search start key the
search occurs in the FAST UP mode.
2 - eventual transitions available on these
inputsareignoredduringthefirst 15search
steps if the system is in the UHF or CATV
bands.
If the system operates in VHF I and III bands,
the first 60 search steps are ignored. The
acceptancedelay of 15 (60) search steps has
been introduced to prevent the system from
stoppingat theprevious station.
After this time the FAST UP speed is
automatically reduced to half during each UP
signal(MEDIUM UP = FAST UP/2).
A DOWN signal preceded by at least an UP
signal will set the search to MEDIUM DOWN
mode (FAST UP/4).
3 - the next UPsignal will switch the search to
SLOWUP speed(61Hz).
At this point the systems is in normal AFT
operation.
B) Digital AFT operation : when a station is
perfectly tuned, the input signals coming from
TDA4433are at middlecondition.
If the tuning moves lower than the threshold
below 38.9MHz,the Pin 12 is put H andPin 13
is put L ; the 13 bit internal counter is moved
SLOW UP speed to increase the varicap
voltage.
When a detuning occurs in the opposite
direction the input 12 goes Low and 13 goes
High and the tuning voltage falls at VERY
SLOWDOWN speed (7.6Hz).
The increaseor decreaseof the tuningvoltage
is stopped as soon as the input returns to
middle conditions.
Thereforeduring normaloperationPins 12 and
13 act asdigital AFT control commands.
C)
Recall from memory:
whenthe digitalAFT is
enabled and data is recalled from Memory, a
fixed valueof 8steps (
≈
31.2mV) is subtracted
from the tuningvoltage.
This corresponds to a detuning of 0.6MHz
(UHF) and of0.3MHzin VHFIIIinto that part of
the IFresponsecurvewhichcorrespondstothe
fully transmitted sideband.
At this point the AFT operation takes over as
describedinpointBaboveand theexacttuning
is achievedin about0.2 sec.
This feature increases the AFT capture range
and fullfills the stability requirements of the
tuner, voltage references and the D/A
converter.
If theDigital AFTis disabled(Pin 17atV
SS
), the
memory contentis read without any change.
M491B
9/16
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| M49-20.000-18-30/50/4085 | 制造商:MEC 功能描述:Crystal SMD 20.000MHz HC49S-SMD |
| M49-24.000-18-30/50/4085 | 制造商:MEC Switches A/S 功能描述:Crystal SMD 24.000MHz HC49S-SMD |
| M49-24.576-18-30/50/4085 | 制造商:MEC Switches A/S 功能描述:Crystal SMD 24.576MHz HC49S |
| M49-25.000-18-30/50/4085 | 制造商:MEC 功能描述:Crystal SMD 25.000MHz HC49S-SMD |
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