LA1776M Datasheet, PDF (29/41 Pages) Sanyo Semicon Device – Monolithic Linear IC Single-Chip Tuner IC for Car Radios

LA1776M
5-2. AM SD Pin (pin 39) and the AM SD Adjustment Pin
The LA1776M compares V24 and the reference voltage V55 to operate SD and the IF counter.
S-meter
VCC
Comparator
+
–
50 µA
55
100 kΩ
24
0.47 µF
AM IF
IF Buff Amp.
50 pF
23
51 kΩ
39
100 kΩ
0.022 µF
5V
IF BUFER SD
SEEK
5V
V24PIN
V55
V39
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
5-3. AM Wideband Cut and Detection Output Adjustment Methods
The AM/FM detection output (pin 31) has an output impedance of 10 kΩ in AM mode, and an impedance of a
few tens of ohms in FM mode. Therefore the AM detection output level is lowered by R31 and the AM
wideband frequency characteristics are determined by C31.
FM
detector
VCC
31
R31
C31
VCC
+
AM
detector
10 kΩ
30
Noise canceller
input
50 kΩ
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