LA1781M_09 Datasheet, PDF (39/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

• Separation adjustment (pin 19)
LA1781M
5kΩ
19
To The
subdecoder
20kΩ
0.047μF C
Larger
Fig. 49
The separation is adjusted by modifying the input level to the subdecoder with the variable resistor connected to pin
19. Since only the sub-modulation level is changed by changing the variable resistor setting, the monaural (main)
output level is not changed. Furthermore, degradation of high band separation in the decoder can be avoided if the
impedance of the external capacitor (C) in the subchannel frequency band (23 to 53kHz) is made sufficiently smaller
than the variable resistor.
9. MRC Circuit
VCC
2μA
S-meter
FM
S-meter
6.4kΩ
10kΩ
DC buffer
30kΩ
MRC
3.6kΩ
75pF 1kΩ
24
32
+
Noise amplifiter
High-pass filter with
Fc = 70 kHz + amplifiter
An external transistor equivalent
to the 2SC536 is required
Reason : A QMRC level shifter is
required to allow a simplified MRC
circuit to be used in the LA1781M.
100Ω
QMRC
27
+ _C27
VCC
To the SNC, pin 28
Fig. 50
No.6038-39/48