| Summary: | 碩士 === 樹德科技大學 === 電腦與通訊系碩士班 === 106 === The characteristics of BAW devices and its circuits constructing with the Mason equivalent circuit and the BVD equivalent circuit have surveyed through simulation software. The Mason equivalent circuit is used to simulate the characteristics of BAW devices. The effects of different piezoelectric materials, electrodes and substrates on BAW devices can be analyzed. A series of changes in frequency response can be obtained with a series of parameter adjustments. Because the Mason equivalent circuit simulates the BAW element with ideal conditions, the transmission loss of the elastic wave in the medium, the dielectric loss, or the piezoelectric conversion efficiency, is not easy to estimate.
This study investigates different designs of BAW devices. Take the electrode material as an example, due to their different mass densities, resulting in changes in the frequency of BAW devices. In addition, the thickness of resonant zone is calculated by the relationship among wavelength, wave velocity, and frequency. The resonance increases as the thickness increases. Furthermore, a ratio of C0/Cm can be changed through the external capacitor, which causes the electromechanical coupling coefficient to change and affect the bandwidth.
In the design of the filter, the BVD equivalent circuit is used to extract the data of the actual component. The equivalent RLC components are therefore been calculated. The advantage of the BVD equivalent circuit is that the circuit can be quickly analyzed and the BAW filter can be conveniently formed. Taking the balanced Ladder type filter as an example, the filter can achieve input and output balanced with only a slight difference in the frequency response. The zero position of the series arm and the parallel arm is better than the π-type filter.
The circuit simulation results show that the Ladder type circuit resonators need to consider area matching. It is recommended that the area of the parallel arm unit must be larger than that of the series arm unit. On the other hand, in the area matching of the Lattice type, the area of series arm unit must be larger than the parallel arm unit. Otherwise, it will not be able to get the passband zero. Finally, the combination of the Ladder type and Lattice type circuit is realized. The simulation result shows that the combination circuit compensates the imperfection caused by a single structure.
|
|---|
