SAW Filter Resonator Coupling for Sharpness and Wide Passband

The patent introduces an intermediary component (capacitor) connected in series between the input/output terminal and the resonator, rather than directly connecting the resonator in parallel. This intermediary capacitor mediates the interaction between the signal and resonator, allowing the resonator to contribute to sharpness while the series capacitor configuration prevents excessive capacitance loading that would narrow the passband.

The patent changes the connection configuration parameter from direct parallel connection to series connection with an intermediary capacitor. By modifying the circuit topology and adjusting the capacitance value of the intermediary capacitor, the system achieves both improved sharpness and maintained passband width, resolving the contradiction between these two parameters.

The patent applies the intermediary capacitor principle at the inter-stage connection point. The capacitor is inserted in series between the cascade-connected filter stages, allowing the resonator connected at this point to enhance sharpness without creating excessive capacitance that would reduce the passband width. This series capacitor configuration acts as a buffer that enables sharpness enhancement while preserving bandwidth.

The patent modifies the inter-stage connection parameter by introducing a series capacitor with specific capacitance value. This parameter change transforms the direct connection topology into a capacitive-coupled topology, enabling the resonator to provide sharpness enhancement while the capacitance value is optimized to maintain adequate passband width.