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)： 22/26頁(yè)
文件大?。?/td> 247K
代理商： STV0056A
FM DEMODULATION SOFTWARE ROUTINE
With theSTV0056Acircuit, foreachchannel,three
stepsare required to acheive a FM demodulation:
- 1
st
step:To setthe demodulationparameters:
FM deviation selection,
Subcarrier frequencyselection.
- 2
nd
step : To implement a waiting loop to check
the actual VCO frequency.
- 3
rd
step:To close the demodulationphaselocked
loop (PLL).
Refering to the FM demodulation block diagram
(page 12), the frequency synthesis block is com-
mon tobothchannels(leftandright); consequently
two completesequenceshavetobe doneoneafter
the other when demodulatingstereo pairs.
Detailed Description
Conventions:
- R = Standsfor Register
- B = Stands for Bit
Example:
R05 B2 = Register 05, Bit 2
For clarity, the explanationsare based on the fol-
lowing example : stereo pair 7.02MHz/L
7.20MHz/R, deviation
±
50kHz max.
1st STEP(LEFT) :
SETTINGTHE DEMODULATION PARAMETERS
A.
TheFM deviationis selected by loading R5 with
the appropriatevalue. (seeR5 truth table).
NB : Very wide deviations(up to
±
592kHz)can be
accomodatedwhen R5 B5 is low.
Corresponding bandwidth can be calculated as
follows :
Bw
≈
2 (FM deviation + audiobandwidth)
Bw
≈
2 (value given in table+ audio bandwidth)
In the example :
R5Bits 7
6
5
4
3
2
X
X
1
1
0
1
1
1
0
0
B.
The subcarrier
launchingafrequencysynthesis(theVCOisdriven
to the wanted frequency). This operation requires
two actions:
- To connect the VCO to the frequency synthesis
loop.ReferingtotheFMblockdiagram(page12):
SW4 closed
R6B2 = H
SW3 to bias
R6 B4 = L
SW2 to bias
R6B3 = L
SW1 opened
R6 B5 = L
- To load R7 and R6 B6 B7 with the value corre-
sponding to the left channel frequency. This 10
bitsvalue is calculatedas follows :
Subcarrierfrequency= coded valuex 10kHz
(10kHz is the minimum step of the frequency
synthesisfunction)
Consideringthat the tunning range is comprised
between5to 10MHz,thecodedvalueisanumber
between500 and 1000 (2
10
= 1024) then 10 bits
are required.
Example:
7.02MHz = 702 x 10kHz
702
1010 1111 10
AF + 10
R7 is loaded with AF and R6 B6 : L, R6 B7 : H.
frequency
is selected
by
The Table1 givesthe settingfor themost common
subcarrier frequencies.
Table 1 :
Frequency SynthesisRegisterSetting
for the Most Common SubcarrierFrequencies
Subcarrier Frequency
(MHz)
Register 7
(Hex)
Register 6
Bit 7
1
0
0
1
0
1
0
0
1
0
0
0
0
1
0
0
1
0
1
0
0
0
0
Bit 6
0
0
0
0
0
0
0
0
0
0
1
0
1
0
0
1
0
0
0
1
0
0
1
5.58
5.76
5.8
5.94
6.2
6.3
6.4
6.48
6.5
6.6
6.65
6.8
6.85
7.02
7.20
7.25
7.38
7.56
7.74
7.85
7.92
8.2
8.65
8B
90
91
94
9B
9D
A0
A2
A2
A5
A6
AA
AB
AF
B4
B5
B8
BD
C1
C4
C6
CD
D8
STV0056A
22/26
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