A Generic Framework for Optimizing Digital Intensive Harmonic Rejection Receivers

Due to the use of switching down converters, harmonic down mixing in wideband wireless application causes distortion to the desired signal. This paper studies this problem with a multi-path down mixing method, which currently is a hot research topic. Digital intensive recombination is proposed fort he first time, in contrast to the traditional "analog recombination"scheme which suffers from the limited harmonic rejection performance due to mismatch among different paths and inaccuracy of scaling factors. A generic framework with mathematical model description is presented in this paper for digital intensive optimization of multi-path harmonic rejection scheme. A mathematical derivation to optimize a generic case with N paths and aiming at rejecting up to the Mth order harmonics is proposed. Additionally, we present an optimal solution to achieve the best harmonic rejection performance for a generic case based on least squares criterion. Specific cases, three and four paths to reject up to the fifth-order harmonics are studied using the proposed mathematical framework. The results show that, theoretically, 18.12dB and complete harmonic rejection can be achieved for three and four paths respectively, which provide mathematical proof for existing multi-path harmonic rejection solutions.