LA1787M Datasheet, PDF (38/54 Pages) Sanyo Semicon Device – Single-Chip Tuner IC for Car Radios

LA1787M
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
±70 kHz of the
received frequency.
Middle AGC
Operates for
80 _{interference within}
±70 kHz 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
30 Ω 0.022 µF
Received frequency:
1 MHz
110
46
–6dB ^{50 Ω}
SG 50 Ω ^{0.022 µF}
100
ANTD
510 Ω
0.022 µF
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
0.022 µF
VCC
30 Ω
620 Ω
1MH
100 µH
FC18
57
100 µH
+
Fig. 35
62
A12084
No. 6655-38/54