LA1781M_09 Datasheet, PDF (12/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

Continued from preceding page.
Pin No.
Pin function
33
Mute drive output
LA1781M
Pin description
•The muting time constant is
determined by an external RC circuit
as described below.
Attack time : TA = 10kΩ × C1
Release time : TR = 50kΩ × C1
•Noise convergence adjustment
The noise convergence can be
adjusted when there is no input
signal by inserting a resistor
between pin 33 and ground.
•Muting off function
Ground pin 33 through a 4kΩ
resistor.
SEEK
OFF
Equivalent circuit
C1
+
0.1μF
VCC
33
50kΩ
10kΩ
MUTE
AMP.
SOFT HOLE Band
MUTE DET muting
50kΩ
SD circuit
34
AGC
35
QD output
36
QD input
37
VREF
38
FM SD ADJ
•The resistor R1 determines the width
of the band muting function.
Increasing the value of R1 narrows
the band.
Reducing the value of R1 widens the
band.
•Null voltage
When tuned, the voltage between
pins 34 and 37, V34 _{- 37,} will be 0V.
The band muting function turns
on when |V34 _{- 37|} ≥ 0.7V.
V37 = 4.9V
0.1μF _VREF
R1
VCC
C
R2
37
36
35
34
VCC
Quadrature
detector
HOLE
DET
3pF
1kΩ
A 130μA current flows from pin 38
and, in conjunction with the external
resistance R, determines the
comparison voltage.
IF limiter amplifier
R
SD ADJ
38
Band
muting
130μA
SD
Comparator
24
S-meter
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