LA1235 Datasheet, PDF (4/12 Pages) Sanyo Semicon Device – FM IF System Applications

LA1235
• Setting of muting sensitivity, hysteresis width (Refer to the
equivalent circuit block diagram and application circuit).
Muting sensitivity and hysteresis width are set arbitarily by
varying resistors R₂₀₄ and R₂₀₅ connected to pins 15 and 16,
respectively. Muting sensitivity is set by varying R₂₀₄ ; and
if R₂₀₄ is made larger, muting sensitivity will shift to the
weak signal side. Hysteresis width is set by varying R₂₀₅ ;
and if R₂₀₅ is made larger, hysteresis width will narrow.
Next, how to set muting sensitivity is concretely described as
follows. In case of using R₂₀₄=50kΩ (semifixed resistor)
and R₂₀₅=56kΩ, the upper limit of current I₁₆, 50µA,
delivered from the signal meter driver at which muting is
turned ON is obtained from the first quadrant of Table for
muting adjustable lower limit calculation. Muting is turned
ON at I₁₆≤50µA. If I₁₆≤50µA, muting is already turned ON
at a point of input being stronger than the setting input and it
is impossible to adjust muting at the setting input. Therefore,
I₁₆>50µA is required at the setting input. The input at which
a sample with a small I₁₆ output meets 50µA is obtained as
V_IN=47dBµ. This input is the maximum value of muting
sensitivity, that is to say, the lower limit at with muting can
be set. The data for sample with a Small I₁₆ shown in this
Table is colose to the minimum value, but since samples
with values less than this munimum value may occur, a
margin of some dBµ must be allowed. From the above, the
minimum value for muting setting (muting ON input)
becomes 50dBµ for R₂₀₄ (semifixed resistor)=50kΩ and
R₂₀₅=56kΩ.
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