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參數(shù)資料
| 型號(hào)： | LA1235 |
| 廠商： | Sanyo Electric Co.,Ltd. |
| 英文描述： | FM IF System Applications |
| 中文描述： | 調(diào)頻中頻系統(tǒng)應(yīng)用 |
| 文件頁(yè)數(shù)： | 5/12頁(yè) |
| 文件大?。?/td> | 1031K |
| 代理商： | LA1235 |
LA1235
No.873-5/12
Setting of muting circuit constnats
Drive current to be output at muting drive output pin 12 is 0.75mA typ., but
approximately 0.4mA may be caused by variations in characteristic or
changes in temperature (smaller at higher temperatures). It is desirable to
design the circuit so that the total current to be output from pin 12 at the time
of muting ON does not exceed 0.35mA. When driving the muting circuit of
the LA1235, the muting drive current (input current at pin 5) must be
considered besides this total output current. The muting drive current of the
LA1235 is 0.2mA max.
Thus, the muting constants are obrained as follows. If the muting drive
current is I
R207
≥
0.2mA, R
207
≤
14k
occurs and the total current It is shown
by the following expression.
If R
207
=10k
is taken with the variation s in voltage V
12
at pin 12 and input resistance 10k
at pin 5 considered,
R
206
≈
56.4k
is obtained, and then R
206
=68k
and R
207
=10k
are obtained.
Setting of C
112
(Capacitance between pin 12 and ground)
C
112
influences S/N and muting attenuation. S/N is improved 0.5 to 2.0dB by changing C
112
from 1μF to 100μF.
Muting attenuation becomes as shown in Mute (att) – fm (next page) characteristic. This phenomenon occurs
because the output at pin 7 appears at pin 6 through pin 10 and capacitance C
110
between pin 7 and ground also exerts
influence. The relation between muting attenuation andC
110
is such that if C
110
=2.2μF and C
112
=220μF, attenuation
at modulation frequency 100Hz becomes –80dB.
AF Output Circuit
It=I
R206
+I
R207
=
+
6.2V
R
206
4.8V
R
206
+10k
(10k
: Input resistance at pin 5, Refer to the above figure.)
Muting Circuit
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