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參數資料
| 型號： | LA1781M |
| 元件分類： | 接收器 |
| 英文描述： | AM/FM, AUDIO SINGLE CHIP RECEIVER, PQFP64 |
| 封裝： | 14 X 14 MM, QIP-64 |
| 文件頁數： | 21/48頁 |
| 文件大小： | 508K |
| 代理商： | LA1781M |
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LA1781M
No.6038-28/48
Transient response characteristics during automatic tuning
The transient characteristics for SD and IF count buffer on/off operation are determined by the time constants of the
RC circuits attached to the following pins.
(1) Muting time constant : pin 33
(2) S-meter time constant : pin 24
(3) AFC time constant : pin 34
There are two points that require consideration when using fast tuning.
(1) The SD time constant due to the S-meter time constant
Since the current I24 (pin 24) varies with the field strength, the time constant also changes. There is no hysteresis in
the comparator.
If C24 is made smaller and the pin 24 voltage is used for the keyed AGC pin 23, C23 must be chosen so that AGC
during keyed AGC operation does not become unstable.
Fig. 15
(2) The SD time constant due to the pin 33 muting voltage time constant
The changes in volume due to field fluctuation during weak field reception can be made smoother by setting the
attack and release times during soft muting operation.
Fig. 16
24
S-meter
I24
SD comparator
C24
R24
Mute
amp
Mute
drive
10k
Ω
50k
Ω
C33
33
Attack
Release
Muting time constants
Attack : 10k
Ω × C33
Release : 50k
Ω × C33
SD Sensitivity Adjustment
0
10
20
30
40
50
630
26
22
18
14
10
34
Resistance between the pin and ground -- k
Ω
Antenna
input
such
that
pin
5
goes
high
-
dB
μ
Fig. 17
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