Design of GSM/DCS dual-band bulk acoustic wave coupled resonator filter with unified input

This work presents the design methodologies and simulation results of a GSM900/DCS1800 dual-band filter based on bulk acoustic wave coupled resonator filter (BAW CRF) technology. The dual-band filter is featured with a unified input port, thus eliminating the need for a RF switch to route the GSM/DCS receiver signals in a GSM/DCS handset. The filter has the ability to deliver a single-ended to differential response and 50 Ohm to 150 Ohm impedance transformation at both GSM and DCS bands. One-dimensional Mason model has been built to predict the behaviours of the filter over large frequency range. Some novel approaches to deal with the coupling layer capacitance to achieve desirable specifications such as fast roll-off and good amplitude/phase imbalances are proposed in this paper.