LA3410 データシートの表示（PDF） - SANYO -> Panasonic
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LA3410 Datasheet PDF : 13 Pages
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LA3410
Decoder circuit (Refer to the Block Diagram in the Sample Application Circuit.)
The LA3410 adopts a decoder circuit of chopper type. The sub signal sync-detected by this decoder is applied to the
post amplifier minus input through RB as shown in the Sample Application Circuit. This signal is matrixed with the
main signal coming out of A3. The demodulation method is, in a sense, a combination of switching method and matrix
method. The gain for the sub signal is :
VS
R1
RB
·
2
π
or
VS
R2
RB
·
2
π
The gain for the main signal is :
VM
VR1
RA+VR1
·
R1
RC
or
VM
VR1
RA+VR1
·
R2
RC
R1, R2 : Post amplifier feedback resistor
VS : Peak value of input sub signal
VR1 : Semifixed resistor for separation adjust
VM : Peak value of input main signal
In the LA3410, the gain of the main signal is varied with VR1 to adjust the separation. The IF output is generally such
that the sub signal level is lower than the main signal level. In this case also, the separation can be adjusted.
3. De-emphasis
The de-emphasis characteristic depends on the feedback resistors, capacitors of the post amplifier. R1, R2, C3, C4 in
the Sample Application Circuit are set as R1C3=R2C4=50µs, 75µs. Table 3 shows the values of R1, R2, C3, C4 and the
de-emphasis constants.
Table 3
R1 (R2)
C2 (C4)50µs
C2 (C4)75µs
33kΩ
1500pF
2200pF
39kΩ
1200pF
2000pF
51kΩ
1000pF
1500pF
62kΩ
750pF
1000pF
82kΩ
620pF
910pF
110kΩ
470pF
680pF
130kΩ
390pF
560pF
The post amplifier requires feedback capacitors C3, C4 regardless of the de-emphasis characteristic. Without these
capacitors, the stereo distortion gets worse.
4. Low-pass filter
Fig. 8 shows a sample circuit configuration where an LC filter is used as the low-pass filter and Fig. 16 shows a sample
characteristic of this filter. As compared with the LPF (BL-13) in the Sample Application Circuit, the use of this filter
makes the attenuation less at 19kHz, 38kHz ; therefore, carrier leak at the LPF output causes the stereo distortion and
separation characteristic to get worse than specified in the Operating Characteristics. For the stereo distortion, the BL-
13 provides approximately 0.02%, while the LC filter provides approximately 0.5%
No.1407–9/13
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