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No. 6038-33/50
LA1781M
0
2
4
6
8
0
2
4
6
0
2
4
6
–1
0
1
2
97.8
97.9
Frequency, fr — MHz
98.0
98.1
98.2
98.3
f2 = 97.9 MHz, 120 dB
μ
fm = 400 Hz, 22.5 kHz dev.
f1 = 98.1 MHz, 120 dB
μ
fm = 1 kHz, 22. 5kHz dev.
When the tuner is moved in 50 kHz steps.
With a 51 k
resistor between pins 37 and 34.
With the SD sensitivity adjusted to be 20 dB
μ
.
P
P
P
V
Unique Features of the LA1781M Hall Detection Circuit (1)
f1
f2
ANT
IN
Fig.27
0
2
4
6
8
0
2
4
6
0
2
4
6
–1
0
1
2
97.8
97.9
Frequency, fr — MHz
98.0
98.1
98.2
98.3
f2 = 97.9 MHz, 40 dB
μ
fm = 400 Hz, 22.5 kHz dev.
f1 = 98.1 MHz, 40 dB
μ
fm = 1 kHz, 22.5 kHz dev.
When the tuner is moved in 50 kHz steps.
With a 51 k
resistor between pins 37 and 34.
With the SD sensitivity adjusted to be 20 dB
μ
.
P
P
P
V
Unique Features of the LA1781M Hall Detection Circuit (2)
Fig.28
Notes on the quadrature input level
When a strong field is being received the quadrature signal input (pin 36) requires a 200 mV rms input, and the
detection transformer and the damping resistor between pins 36 and 37 must be designed.
(We recommend the Sumida SA-208 transformer and a 10 k
resistor between pins 36 and 37.)
When the pin 36 input level falls below 160 mV rms, the Hall detection circuit operates and the pin 33 mute drive
output voltage increases. Therefore, when pin 36 input is from 160 to under 200 mV rms during strong field
reception, the muting circuit may or may not operate due to sample-to-sample variations between individual ICs.
Furthermore, the SD function may not operate, and the audio output level may be reduced. Incorrect operation due
to sample-to-sample variations and temperature characteristics can be prevented by keeping the pin 36 voltage at
200 mVrms or higher.
0
92
1
2
3
4
5
6
94
96
98
100
102
104
106
With pins 34 and 37 shorted.
With 5 V applied to pin 24.
V
QD input level — dB
μ
Pin 33 VMute — QD Input Level
36
37
SG
10.7 MHz
LA1888M
75
75
+
0.022
μ
F
Fig.29
–0.8
–0.6
–0.4
–0.2
0.2
0.4
0.6
0.8
1
2
3
4
–100 –80 –60 –40 –20
–120
With the resistor between
pins 36 and 37 open.
With a 10 k
resistor
between pins 36 and 37.
0
20
40
f — kHz
60
80
100 120
f=0
→
10.7 MHz
Voltage between pins 37 and 34
(referenced to the pin 37 voltage)
THD 1 kHz
75 kHz dev
SA208 + LA1781M IF Input Characteristics
T
Fig.30