LA1781M_09 Datasheet, PDF (29/48 Pages) Sanyo Semicon Device – For Car Radios Single-Chip Tuner IC

LA1781M
However, when testing this stop sensitivity, note that when checking the waveform on the IF count buffer output
(pin 23), there are cases, such as that shown below, where current in the test system may be seen as flowing to
ground and cause oscillation that causes the IF count buffer output to go to the output state.
F.E.
IF
IF BUFFER
AMP
5V
0.022μF
Test system capacitance
The 10.7MHz feeds back through ground.
Fig. 18
• FM Muting control pin (pin 47) (R47 : 30kΩ variable resistor)
The -3dB limiting sensitivity can be adjusted with R47.
10
0
--10
--20
--30
--40
--50
--60
--70
--20
FM Soft Muting (1)
Fig. 19
15kΩ
R47 = 7.5kΩ
DET out
10kΩ
20kΩ
Noise
--10
0
10
20
30
40
Antenna input -- dBμ
• FM muting attenuation adjustment (pin 58)
The muting attenuation can be switched between the three levels of -20, -30, and -40dB by the resistor inserted
between pin 58 and ground. (Note that the exact values depend on the total tuner gain.)
The noise convergence with no input is determined by the pin 58 voltage.
58
100Ω R58
33
R58
Open
200kΩ
30kΩ
Mute ATT
-20dB
-30dB
-40dB
The attenuation can be set by making R33 smaller as listed
in the table above.
R33
Fig. 20
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