LA1787M Datasheet, PDF (43/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

• Separation adjustment (pin 19)
LA1787M
5 kΩ
19
To the
subdecoder
20 kΩ
0.047 µF C
Larger
A12094
A12093
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 53 kHz) is made sufficiently
smaller than the variable resistor.
6. MRC Circuit
S-meter
FM
S-meter
6.4 kΩ
10 kΩ
DC buffer
30 kΩ
MRC
3.6 kΩ
75 pF 1 kΩ
24
32
+
Noise amplifier
High-pass filter with
Fc = 70 kHz + amplifier
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 LA1787M.
Fig. 50
VCC
2 µA
100 Ω
QMRC
27
+ _C27
VCC
To the SNC, pin 28
A11768
No. 6655-43/54