Two-Tone Vs. Single-Tone Measurement Of Second-Order Non-Linearity And IP2 Performance Of Direct Conversion ReceiversSource: Skyworks Solutions, Inc.
This article describes how to find the second-order intercept point (IP2) from one-tone and two-tone tests of Direct Conversion Receivers (DCRs). It also presents measurement results for the GSM900 receive path, as used in the AMPS band, for Skyworks first-generation of DCRs.
Relation Between 2-Tone and 1-Tone Tests for Second-Order Non-linearity
Second order non-linearity is an important phenomenon in DCR-type receivers. Here we set out to show the test result of this kind of non-linearity, which can be used to predict the DC offset, both with single tone or two tones. A two-tone condition is illustrated in Figure 1 and Figure 2.
The relationship between f1, f2 and f3, f4 is:
f3 = f2 - f1
Likewise for f4:
f4 = f2 + f1
This shows that the unwanted output frequency components are mathematically related to the input tones. To have a better insight into the relationship between undesired components and the input terms, a more rigorous derivation is needed.
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Application Note: Two-Tone Vs. Single-Tone Measurement Of Second-Order Non-Linearity And IP2 Performance Of Direct Conversion Receivers