SI4742 查看數據表（PDF） - Silicon Laboratories
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SI4742 Datasheet PDF : 68 Pages
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AN388
2.3.8. IP3
Intermodulation distortion in the detected or decoded audio-frequency signal may be caused by non-linearity in the
radio-frequency, intermediate-frequency, and detector stages of the receiver. A good measure of intermodulation
distortion is IP3. IP3 is the theoretical RF level at which two blockers (VRF1), offset from the desired frequency by
f and 2f, and their intermodulation product (VRF0) would be of the same amplitude, according to the equation
IP3 = VRF1 + ½(VRF1 – VRF0).
VRF0 is the 26 dB SINAD sensitivity level at the fundamental frequency. VRF1 is the blocker level required to
produce an inter-modulation product at the same sensitivity level.
2*f1-f2 f1 f2 2*f2-f1
Figure 4. Graphical Representation of IP3
In our test:
f1 = 102.1 MHz (blocker #1)
f2 = 106.1 MHz (blocker #2)
2*f1-f2 = 98.1 MHz (tuner frequency)
1. Connect test equipment as shown in Figures 1, 2, or 3.
2. Make a sensitivity measurement, VRF0, as described above.
3. Configure the tuner in standard configuration, except for the AGC setting. For this section of the test, set AGC
OFF.
4. Configure the audio analyzer:
a. Select Analyze.
b. Set Function = THD+N / SINAD.
i. Set Measurement Mode = SINAD.
ii. Select Unit = dB.
Rev. 0.2
19
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