Design Of Bulk Acoustic Wave Duplexer For FDD-LTE

The bulk acoustic wave(BAW) duplexer composed of thin film bulk acoustic wave resonator(FBAR)s can meet the requirements of high performance RF front end filtering in 4G/LTE application, becoming a novel solution of RF duplexer. According to the FDDLTE Band 7, one of the most widely used frequency band in mobile phone, a BAW duplexer with insertion loss of 1.5 dB and isolation of 46 d B is designed. Aiming at the issues about BAW duplexer in design, Such as improvement of FBAR circuit model, design of Tx and Rx filtersand design of phase shifter, some corresponding solutions have been provided.For the improvement of FBAR MBVD circuit model, a method of extracting the parameters of FBAR performance model is established. The error of the prediction and the measured value of the performance model is within 3%. For the improvement of Mason FBAR circuit model, the finite element simulation method is used to consider the two kinds of energy loss mechanisms of FBAR. The new parameters of the circuit model is extracted by the method of FBAR impedance curve fitting.For the design of Tx and Rx filter, the factors that affect the performance of the filter are analyzed. And a method of parametric design for BAW filter by steps is proposed. The design of the Tx and Rx filters are presented, which meets the technical specifications.For the design of phase shifter, the ? type LC circuit structure is adopted. The planar meander inductor with Q value of 20 is designed by increasing the thickness of the metal layer and the line width. By the method of thickening the top electrode of FBAR, a kind of "BAW" capacitor, which is compatible with FBAR process, is designed, and the Q value of it is about 20. The phase shift and insertion loss of the phase shifter is 90.3 degrees and 0.8 dB at 2535 MHz respectively, which meet the design requirements.Load effect of Rx filter for Tx filter in Bulk acoustic wave(BAW) duplexer brings about the degradation of insertion loss and excess out band rejection of Tx filter, which makes the BAW duplexer poor performance. In order to solve this problem, a design method of optimization for BAW duplexer is proposed. The resonance area of series FBAR and ratio of resonance area of parallel FBAR to series FBAR are made into two groups of optimization variables. By sacrificing the excess out band rejection of Tx filter, gradient base optimization algorithm is used to obtain the final value of the two groups of the optimization variables.