Diagnosis of Double-Mode Surface Acoustic Wave Resonator Filters Based on Equivalent Circuit Analysis

This article describes the diagnosis of double-mode surface acoustic wave (DMS) filters based on equivalent circuit analysis. It provides a detailed discussion on methods for deriving an equivalent circuit from the measured admittance matrix [Y] and determining the LCR values in the circuit. Detailed discussions are given on the impact of parasitic impedance elements appearing in the derived circuit. First, [Y] is decomposed into three parts, i.e., symmetric, antisymmetric, and asymmetric ones, and they are expressed by the modified Butterworth-Van Dyke (mBVD) model, including multiple mechanical branches. Tips to determine the circuit elements in the case are also disclosed. Then, the measured data of a DMS filter at the underdevelopment level are used as an example to explain the fitting procedures step by step. It is also shown how various secondary effects appear in the equivalent circuit and how their effects appear in the total filter responses. Finally, the current modeling technique is applied to another DMS filter at the production level, demonstrating the accuracy of the presented modeling technique.