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參數(shù)資料
| 型號： | STV0056AF |
| 廠商： | 意法半導(dǎo)體 |
| 英文描述： | Satellite Sound and Video Processor(衛(wèi)星探測和視頻處理器) |
| 中文描述： | 衛(wèi)星聲音和視頻處理器（衛(wèi)星探測和視頻處理器） |
| 文件頁數(shù)： | 10/27頁 |
| 文件大?。?/td> | 224K |
| 代理商： | STV0056AF |
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CIRCUIT DESCRIPTION
VideoSection
The compositevideo is first set to a standard level
by means of a 64 stepgain controlledamplifier. In
thecasethat themodulationisnegative,an inverter
can be switchedin.
One of two different external video de-emphasis
networks (for instance PAL and NTSC) is select-
able by an integrated bus controlledswitch.
Then energy dispersal is removed by a sync tip
clamping circuit, which is used on all inputs to a
video switching matrix, thus making sure that no
DC steps occur when switching video sources.
The matrix can be used to feedvideo to and from
decoders,VCR’sand TV’s.
A bus controlled black level adjustment circuit is
provided on the decoder output allowing a direct
connectionto an on-board Videocryptdecoder.
Additionaly all the video outputs are tristate type
(high impedance mode is supported), allowing a
simple parallel connections to the scarts (Twin
tunerapplications).
Audio Section
The two audio channels are totally independent
except for the possibility given to output on both
channelsonlyoneoftheselectedinputaudiochan-
nels.
To allow a very cost effective application, each
channel uses PLL demodulation. Neither external
complexfilter nor ceramic filtersare needed.
The frequency of the demodulated subcarrier is
chosenby a frequencysynthesizer which sets the
frequency of the internal local oscillator by com-
paring
its phase with the internally generated
reference. When the frequency is reached, the
microprocessor switches in the PLL and the de-
modulationstarts.Atanymomentthemicroproces-
sor can read from the device(watchdog registers)
the actual frequencyto which the PLLis locked. It
canalsoverifythatacarrierispresentatthewanted
frequency(by readingAMPLKstatus bit)thanksto
a synchronous amplitude detector, which is also
used forthe audioinput AGC.
In order to maintain constant amplitude of the
recovered audio regardless of variations between
satellitesor subcarriers,the PLLloop gain may be
programmedfrom 56 values.
Any frequency deviation can be accomodated
(from
±
30kHz till
±
400kHz).
Two different networks can be permanently con-
nectedfor either 75
μ
s or J17de-emphasis.If 50
μ
s
de-emphasisis required,thiscan beinsertedbyan
internal switch, thus allowing a worldwide applica-
tion.
The STV0056AFis intendedto be compatiblewith
WegenerPanda System.
Two types of audio outputs are provided: oneis a
fixed 1V
RMS
and the other is a gain controlled
2V
RMS
max. The control range being from +12dB
to -26.75dBwith1.25dBsteps.Thisoutputcanalso
be muted.
A matrixis implementedto feedaudioto andfrom
decoders VCR’s and TV’s.
Noise reduction system and de-emphasis can be
insertedor by-passed throughbus control.
Also all the audio outputs are tristate-type (high
impedancemode is supported),allowing a simple
parallelconnectionsto thescarts(Twintunerappli-
cations).
Others
A22kHz tone is generatedfor LNBcontrol.
It isselectableby bus controland availableon one
of the two pins connected to the external video
de-emphasis networks. One general purpose I/O
is alsoavailable on the STV0056AF.
By means of the I
2
C bus there is the possibility to
drive the ICs into a low power consumption mode
with active audio and video matrixes. Inde-
pendantly from the main power mode, each indi-
vidualaudioandvideooutputcan bedrivento high
impedancemode.
STV0056AF
10/27
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