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SI4741

Si470X/1X/2X/3X/4X EVALUATION BOARD TEST PROCEDURE

Silicon Laboratories 

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 2f, 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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