Adaptive compensation of even-order distortion in direct conversion receivers

Even-order distortion is a severe problem in a direct-conversion receiver. In this paper, we look into the problem of how the even-order distortion is generated in a direct conversion receiver, and then provide a way to compensate for it. The inherent problem of even-order distortion can either be solved by employing only the radio frequency (RF) components with higher second-order input intercept point (IIP2) in the direct-conversion receiver, or by adopting some kind of DSP-assisted distortion compensation. The proposed technique goes for the latter and uses the even-order distortion signal of a low noise amplifier (LNA) as the reference signal to cancel the the even-order distortion of the direct-conversion receiver. This approach enjoys the advantages of: 1) no training sequence is needed; and 2) low complexity. The performance improvement of the direct-conversion receiver brought about by the proposed technique is demonstrated through computer simulation.