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參數(shù)資料
| 型號： | TDA8120B |
| 廠商： | 意法半導體 |
| 英文描述： | MULTISTANDARD VIDEO AND SOUND IF SYSTEM |
| 中文描述： | 多標準視頻和聲音如果系統(tǒng) |
| 文件頁數(shù)： | 5/6頁 |
| 文件大小： | 204K |
| 代理商： | TDA8120B |
The TDA8120B (see block diagram) consists of a
video sectionanda soundsection.The integration
of both sections on the same chip requires a high
isolation at IF frequencies. This is achieved by
physically separatingthe two sections, with sepa-
rate power supplies and ground pins. In addition,
special care has been taken in the choice of pad
positionsfortheIF inputsandsound/videooutputs.
The video section consists of threeAC-coupled IF
stageswith more than60dBAGCrange,flatampli-
tude/frequency response from 10 to 85MHz and
linearized phase slope from 30 to 50MHz. Video
carrierregenerationisperformedbyatunedlimiter.
Thecarrieristhenappliedto thevideodemodulator
througha specialcircuit which switches the carrier
phase from 0 to 180
°
so thatthe videopolarity can
be maintained constant when the standard
switchesfromB/Gto L.Anoiseinverterandawhite
spot inverter are included to eliminate ultra-black
and white pulses.
A top sync or a top white clamping circuit and a
minimum DC videocomponent detectorareimple-
mented by two double comparators the charac-
teristics of which maybe controlledby an external
control input to adapt to the modulation type for
each standard.The voltageat the outputof thetwo
comparatorsismemorizedbyanexternalcapacitor
and used to drive the AGC network, which allows
an input regulation of the video carrier from less
than 100
μ
V to 100mV. A delayed control storage
with current output for the turner AGC completes
the video section.
The sound sectionconsists of three IF stages with
thesame characteristicsasthevideoIFstagesand
an identicalnetwork to control and set the gains of
the three IF amplifiers. The output of the third IF
stage feeds the AM/AGC detector and the QSS
section.
The AM/AGC detector consists of a wideband
limiter for AM sound regeneration or video carrier
regeneration used to feed the synchronousmulti-
plier and consequentlyto obtain the AM demodu-
lated audio signal. In addition, a DC voltage
proportionalto thepeak-to-peakvalue of the video
carrierisproduced.Twocomparatorscompletethe
soundAGC loop.
The subsequent QSS section consists of a refer-
ence amplifier tuned to the video IF which buffers
a wideband limiter to reject completely the video
AM information without introducing incidental
phasemodulation (IPM).
Following the limiter there are a 90
°
phase shifter
and a linear-to-logarithmic converter which drives
a linearmultiplier asademodulatorfortheintercar-
rier 2ndsoundIF.Thisquadraturemultiplierrejects
allvideocomponentstransmittedinDSBthat islow
frequencycomponentsof the video signal.
In addition to the sound and video sections, the
TDA8120Bincludes a block for standard switching
(B/Gor L) controlledby a TTL-compatible input.
CIRCUIT OPERATION
TDA8120B
5/6
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