Acoustic Duplexer Spurious-Mode Tuning for Crossover Interference

The patent converts spurious modes, which are traditionally considered harmful interference, into beneficial elements by intentionally designing resonators to generate spurious signals at frequencies that coincide with the crossover region. These spurious signals create notches in the filter response that actively reduce crossover interference between transmit and receive bands, transforming a previously problematic phenomenon into a solution for improving isolation.

The patent changes the frequency response parameters of the filter by introducing controlled spurious modes at specific frequencies. By adjusting the resonator design parameters (such as aperture size, electrode geometry, and resonator dimensions) to generate spurious signals at the crossover frequency, the filter creates deep notches in the transition band without affecting the passband insertion loss, thus reducing crossover interference while maintaining low energy loss.

The patent eliminates the need for additional interference reduction components by utilizing the inherent spurious modes of the resonators themselves. Instead of adding separate filters or isolation structures that would increase chip area, the design leverages the natural spurious responses of the resonators to create the desired notches in the crossover region, achieving interference reduction within the existing resonator footprint.

The patent achieves steep effective filter slopes in the crossover region by changing the resonator geometric parameters to control the frequency and amplitude of spurious modes. By adjusting parameters such as resonator aperture width, electrode finger dimensions, and resonator spacing, the design creates sharp notches at the crossover frequency without requiring complex multi-stage filtering structures, thus achieving steep effective slopes with relatively simple resonator designs.