LA1781M_09 Datasheet, PDF (27/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

LA1781M
5. FM IF
• Notes on the FM SD and SD adjustment
The figure below presents an overview of the FM SD and the IF count buffer.
Band
muting
HOLE
CLET
S-meter
4.9V
R
+
--
R
+
--
R
Muting
drive
output
STEREO
IND
+
--
39 24
33
IF count buffer
FM IF
23
IF count output
2.5V 5V
26
5V
SD
STEREO/MONO
Fig. 13
Figure 14 shows the relationship between the FM SD, the IF count buffer output, the S-meter, and the muting drive
output.
Larger
V24
values
of R33
V38
S-meter
V33
Smaller values of R33
V26
5V
V23AC
V33
over 0.7V
On as an
SD signal
V23DC
OFF
IF count
buffer
5V
OFF
V33
over 0.7V
SD
SD
Mono
ON
ON ^Stereo
0.7V
IF counter output off
2.5V
0V
RDS and other types of SD detection can be used by switching these modes.
New LA1784M functionality : For stereo input (when the V26 pin voltage is 0.7V),
when this pin is shorted to ground (0.1V or lower)
the IC will operate in forced mono mode.
Fig. 14
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