參數(shù)資料
型號(hào)： STV0056A
廠商： 意法半導(dǎo)體
英文描述： Satellite Sound and Video Processor(衛(wèi)星探測(cè)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(cè)和視頻處理器）
文件頁(yè)數(shù)： 9/26頁(yè)
文件大小： 247K
代理商： STV0056A
CIRCUIT DESCRIPTION
Video Section
The compositevideo is first set to a standardlevel
by means of a 64 stepgain controlled amplifier. In
the casethatthemodulationisnegative,aninverter
can be switched in.
One of two different external video de-emphasis
networks (for instance PAL and NTSC) is select-
able by an integrated bus controlled switch.
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 stepsoccur when switchingvideo sources.
The matrix can be used to feed video 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
tuner applications).
AudioSection
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 filters are needed.
The frequency of the demodulated subcarrier is
chosen by a frequencysynthesizerwhich 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 canread from the device(watchdog registers)
the actualfrequency to whichthe PLL is locked. It
can alsoverify thatacarrierispresentatthewanted
frequency(by reading AMPLK status bit) thanksto
a synchronous amplitude detector, which is also
used forthe audio input AGC.
In order to maintain constant amplitude of the
recovered audio regardless of variationsbetween
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-
nected for either75
μ
s or J17 de-emphasis. If 50
μ
s
de-emphasisis required, thiscan beinsertedbyan
internal switch, thus allowing a worldwide applica-
tion.
The STV0056Ais intended to be compatible with
WegenerPanda System.
Two types of audio outputsare 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 matrix is implemented to feed audio toand from
decoders VCR’s andTV’s.
Noise reduction system and de-emphasis can be
inserted or by-passed through bus control.
Also all the audio outputs are tristate-type (high
impedancemode is supported),allowing a simple
parallelconnectionsto thescarts (Twin tunerappli-
cations).
Others
A22kHz toneis generatedfor LNB control.
It is selectablebybus control and availableon one
of the two pins connected to the external video
de-emphasis networks. One general purpose I/O
is alsoavailable on the STV0056A.
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-
vidualaudio and video outputcan bedrivento high
impedancemode.
STV0056A
9/26
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