LA1781M_09 Datasheet, PDF (34/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

LA1781M
AM AGC f characteristics Fig. 33
Wide AGC
100
Operates for wide
band interference
90
Wide AGC
Operates for
wide band
interference
Middle AGC
Operates for
interference within
±70kHz of the
received frequency.
Middle AGC
Operates for
80 _{interference within}
±70kHz of the
received frequency.
70 ^{Narrow AGC}
Operates at the
received frequency.
60
800
900
1000
1100
1200
Frequency -- Hz
Wide Band AGC Circuit Fig. 34
120
Received frequency :
30Ω
0.022μF
1MHz
110
46
--6dB ^50Ω
SG 50Ω ^0.022μF
100
ANTD
0.022μF
510Ω
90
80
70
1.0
2
3
5 7 ₁₀
2
3
5
Pin 46 input -- MHz
The wide band AGC circuit in this IC has the frequency characteristics shown above. The pin 46 input frequency
characteristics are identical to those of the RF amplifier gate. This AGC circuit serves to prevent distortion at the FET
input when a strong signal is applied to the antenna circuit. The level at which the AGC circuit turns on can be
adjusted to an arbitrary level with the wide band AGC adjustment resistor. A delayed AGC on level can be handled by
reducing the value of the adjustment resistor.
Wide band AGC adjustment resistor
0.022μF
VCC
30Ω
620Ω
1MH
100μH
FC18
57
100μH
+
62
Fig. 35
No.6038-34/48