Ladder-lattice bulk acoustic wave filters: Concepts, design, and implementation

This article presents a study of ladder-lattice bulk acoustic wave (BAW) filters. First, a review of BAW technology and filters topologies is addressed. Next, a mixed ladder-lattice BAW filter for application on W-CDMA reception front-ends (2.11–2.17 GHz) is presented. An improved solidly mounted resonators (SMR) technology was used for the filter implementation. The filter synthesis methodology is briefly described. Layout guidelines are discussed enabling an optimized filter design. The filter on-wafer measurement results are as follows: −3.55 dB of insertion loss, −8.7 dB of return loss, an isolation higher than −47 dB at the transmission band (1.92–1.98 GHz) and an improved selectivity (−30 dB at 2.14 GHz ± 60 MHz). Therefore, we can observe that the mixed topology combines the advantages of ladder and lattice networks, having very steep responses and an improved isolation at undesired bands.