As LTE offers the best wireless experience as never before, people spend much more time on smartphones to enjoy internet surfing and social networking, etc. To further improve the LTE network efficiency, recently, the Power-Class 2 (PC2) High Power User Equipment (HPUE) applied to B41 is deployed. To support HPUE, RF transmitters (TXs) need to deliver higher output power while maintaining stringent linearity requirements of emission mask, especially for third-order Counter Intermodulation (CIM3) in one Resource Block (1RB) case. CIM3 can be improved by several techniques such as power mixers [1,2], Harmonic-Reject Mixers (HRM) [3], notch-filter mixers [4, 5] and digital TXs [6]. Power-mixer, HRM and digital TX solutions may not be suitable for HPUE due to power-efficiency limitations. The notch-filter mixer is based on a voltage-mode passive mixer with 25%-duty-cycle LO, and it reduces 3flo, which exactly corresponds to the component at 3flo-fbb, by employing an LC trap. However, the conventional series [4] or parallel [5] 3flo trap causes a significant insertion loss at flo, which exactly corresponds to the component at flo+fbb, due to the trade-off between its efficiency, 3flo suppression and tuning range. This work presents a new transformer-based notch filter mixer. In this structure, the 3flo suppression can automatically track the channel frequency resulting in a wide operation frequency range of 1.4GHz to 2.7GHz while both the power efficiency and 3flo suppression are improved compared with the conventional notch-filter mixer [4,5].
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