LA1781M_09 Datasheet, PDF (35/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

LA1781M
• Notes on AM SD (pin 26) and the SD adjustment pin
SD and the IF buffer are operated by comparing the S-meter level (V24) and the 5V reference voltage as shown in
figure 36.
S-meter
VCC
50μA
Comparator
+
--
AM IF
IF buff amp.
50pF
55
100kΩ
24
0.47μF
23
26
100kΩ
51kΩ
0.022μF
5V
IF buffer SD
Seek
5V
Fig.36
Figure 37 shows the relationship between the AM SD, the IF count buffer, and the S-meter.
V24PIN
V55
V26
Larger
values
of R55
S-meter
Smaller values of R55
V23AC
SD on
OFF
IF buffer on
V23DC
5V
Pin 55 AM SD adjustment pin
0V
Fig.37
AM SD Sensitivity Adjustment Fig. 38
80
70
60
50
40
30
20
10
0
0
10
20
30
40
50
Resistance between pin 55 and ground -- kΩ
No.6038-35/48