STV0056A STMicroelectronics, STV0056A Datasheet - Page 22

• Manufacturer Part Number: STV0056A
• Description: Video ICs Analog Sound/Video
• Manufacturer: STMicroelectronics
• Type: Audio DSPr

Specifications of STV0056A

• Maximum Operating Temperature: + 70 C
• Package / Case: PDIP-56
• Minimum Operating Temperature: 0 C
• Mounting Style: Through Hole
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

STV0056A
FM DEMODULATION SOFTWARE ROUTINE
With the STV0056A circuit, for each channel, three
steps are required to acheive a FM demodulation :
- 1
- 2
- 3
Refering to the FM demodulation block diagram
(page 12), the frequency synthesis block is com-
mon to both channels (left and right) ; consequently
1st STEP (LEFT) : SETTING THE DEMODULATION PARAMETERS
A. The FM deviation is selected by loading R5 with
the appropriate value. (see R5 truth table).
NB : Very wide deviations (up to 592kHz) can be
accomodated when R5 B5 is low.
Corresponding bandwidth can be calculated as
follows :
Bw
Bw
In the example :
R5 Bits 7
B. The subcarrier frequency is selected by
launching a frequencysynthesis (the VCO is driven
to the wanted frequency). This operation requires
two actions :
- To connect the VCO to the frequency synthesis
- To load R7 and R6 B6 B7 with the value corre-
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the actual VCO frequency.
loop (PLL).
loop. Refering to the FM block diagram (page 12):
sponding to the left channel frequency. This 10
bits value is calculated as follows :
Subcarrier frequency = coded value x 10kHz
(10kHz is the minimum step of the frequency
synthesis function)
Considering that the tunning range is comprised
between 5 to 10MHz, the coded value is a number
between 500 and 1000 (2
are required.
Example :
7.02MHz = 702 x 10kHz
702
R7 is loaded with AF and R6 B6 : L, R6 B7 : H.
st
nd
rd
FM deviation selection,
Subcarrier frequency selection.
SW4 closed
SW3 to bias
SW2 to bias
SW1 opened
step :To set the demodulation parameters :
step :To close the demodulation phase locked
step : To implement a waiting loop to check
2 (FM deviation + audio bandwidth)
2 (value given in table + audio bandwidth)
X
1010 1111 10
6
X
5
1
R6 B2 = H
R6 B4 = L
R6 B3 = L
R6 B5 = L
4
1
10
AF + 10
3
0
= 1024) then 10 bits
2
1
1
1
0
0
two complete sequences have to be done one after
the other when demodulating stereo pairs.
Detailed Description
Conventions :
- R = Stands for Register
- B = Stands for Bit
Example : R05 B2 = Register 05, Bit 2
For clarity, the explanations are based on the fol-
lo win g exa mple : st ereo pa ir 7 . 02MHz /L
7.20MHz/R, deviation 50kHz max.
The Table 1 gives the setting for the most common
subcarrier frequencies.
Table 1 : Frequency Synthesis Register Setting
for the Most Common Subcarrier Frequencies
Subcarrier Frequency
(MHz)
5.58
5.76
5.94
6.48
6.65
6.85
7.02
7.20
7.25
7.38
7.56
7.74
7.85
7.92
8.65
5.8
6.2
6.3
6.4
6.5
6.6
6.8
8.2
Register 7
(Hex)
BD
CD
8B
9B
9D
A0
A2
A2
A5
A6
AA
AB
AF
B4
B5
B8
C1
C4
C6
D8
90
91
94
Bit 7
Register 6
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