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參數(shù)資料
| 型號： | STV0056A |
| 廠商： | 意法半導體 |
| 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)： | 23/26頁 |
| 文件大?。?/td> | 247K |
| 代理商： | STV0056A |
FM DEMODULATION SOFTWARE ROUTINE
(continued)
2
nd
STEP (LEFT) :
VCO FREQUENCYCHECKING (VCO)
This second step is actuallya waiting loopinwhich
the actual runningfrequency of the VCO is meas-
ured.
To exit of this loop is allowed when : Subcarrier
Frequency- 10kHz
≤
MeasuredFrequency
≤
Sub-
carrier Frequency + 10kHz (
±
10kHz is the maxi-
mum dispersion of the frequency synthesis
function).
In practice, R8 B2 B3 and R9 are read and com-
pared to the value loaded in R6 B6 B7 and R7
±
1 bit.
Note :
The duration of this stepdepends on how large is
frequency difference between the start frequency
and the targeted frequency.Typically :
- the rate of changeof the VCOfrequencyis about
3.75MHz/s(C
pump
= 10
μ
F)
- In addition to this settling time, 100ms must be
addedto takeinto accountthe samplingperiodof
the watchdog.
3
rd
STEP (LEFT)
The FMdemodulationcanbestartedbyconnecting
the VCOto the phaselocked loop (PLL).
In practice:
- SW3 closed
R6B4 = H
- SW4 opened
R6 B2 = L
After this sequence of 3 steps for left channel,
a similar sequenceis neededfor the rightchannel.
Note :
In the sequencefor the right, there is no need to
again select the FMdeviation (once is enough for
the pair).
General Remark
Before to enable the demodulated signal to the
audiooutput,it isrecommandedto keepthe muting
and to check whethera subcarrieris present at the
wantedfrequency.Suchaninformationisavailable
in R8 B0 and R8 B4 whichcan be read.
Two differentstrategiescanbe adoptedwhenena-
bling the output :
- Eitherboth left andrightdemodulatedsignalsare
simultaneously authorized when both channel
are ready.
- Orwhile therightchannelsequenceis running,the
alreadyready left signalis sentto theleft andright
outputs and the real stereo sound L/R is output
whenbothchannelsare ready.This secondoption
givessounda fewhundredsof ms beforethe first
one.
STV0056A
23/26
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