ABSTRACT
Second-order intermodulation distortion (IM2) has been much less of a concern historically for the radio receiver designer than third-order intermodulation distortion (IM3). This has been the case since IM2 products mostly fell out-of-band for narrowband receivers, while significant levels of IM3 could easily fall in-band. With the adoption of the homodyne, or zero-IF, and low-IF receivers (see Figure 2.1), this situation has changed. Amplitude-modulated signals will generate IM2 at baseband frequencies, for example, due to a strong adjacent channel interferer or due to own transmitter leakage. Even if these baseband IM2 products are generated before the mixer, they may still leak through the mixer due to a nonzero DC offset. When the nonlinearity is in the baseband circuitry, all such IM2 will directly become co-channel interference.
