CXA3117AN 查看數據表（PDF） - Sony Semiconductor
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CXA3117AN Datasheet PDF : 30 Pages
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CXA3117AN
18) Sensitivity Adjustment Method
The constants shown in the Application Circuit diagram are for the standard external parts. However,
adjustment may be necessary depending on the conditions of use, characteristics of external parts, and the
RF system circuit and decoder connected to the IF IC, etc. Adjust the sensitivity according to the following
procedures.
a) MIX IN matching
When using a matching circuit between the RF system circuit and MIX IN of the CXA3117N, adjust the
trimmer to obtain the optimal sensitivity while monitoring the AUDIO output.
b) Local input level
The mixer circuit gain is dependent on the local signal input level to OSC IN. The input level to OSC IN
should be set as high as possible within the range of –6 to +2dBm as shown in the graph of "Local input
level vs. Mixer gain characteristics". However, care should be taken as raising the input level above +2dBm
will cause the sensitivity to drop.
When creating the local signal using the internal oscillator circuit, the oscillation level varies according to
the external capacitances attached to Pins 1 and 2 and the characteristics of the used crystal. Therefore,
be sure to adjust the external capacitance values attached to Pins 1 and 2 according to the crystal
characteristics.
OSC
1
2
VCC
C1
C2
C1 and C2 have the following range in the figure above.
C1 ≥ C2
C1 = C2 to C1 = 5C2
As for the ratio of C1 to C2, the oscillation stabilizes as C1 approaches equality with C2.
The oscillation level decreases as the C1 and C2 values become larger, and increases as the C1 and C2
values become smaller.
Use a FET probe to confirm the local input level.
c) LPF constant
The data filter cut-off may need to be changed depending on the characteristics of the connected decoder.
Adjust the capacitance values of Pins 9 to 12 while checking the incoming sensitivity including the decoder.
If the capacitance values are too large, the detector output waveform will deviate at high data rates, causing
the sensitivity to drop. Conversely, if the capacitance values are too small, the LPF will be easily affected by
noise, causing the sensitivity to drop.
Adjust capacitance values of Pins 9 to 12 so that the capacitance value described in "16) LPF Constant"
becomes smaller.
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