Acoustic Wave Filter Circuit With Shared Resonators for Low Insertion Loss
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Solution Overview
Problem
Existing acoustic wave filters face challenges of large size and high insertion loss due to the addition of a matching resonator, which fails to reduce matching loss effectively.
Innovation Solution
The design incorporates a first serial-arm resonator and a first parallel-arm resonator on a shared piezoelectric substrate, with the parallel-arm resonator's resonant frequency lower than the low frequency end and anti-resonant frequency higher than the high frequency end of the passband, and includes a series-connected inductor to broaden the resonant bandwidth, ensuring low loss and reduced size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a matching resonator is added to reduce matching loss, then impedance matching is improved, but insertion loss increases and device size increases
Solution Approach 1:
The invention extracts the matching function from a separate matching resonator and integrates it into the parallel-arm resonator itself. By configuring the parallel-arm resonator with specific resonant and anti-resonant frequencies that overlap the passband, the resonator simultaneously performs both filtering and impedance matching functions, eliminating the need for an additional matching component and reducing insertion loss.
Solution Approach 2:
The invention merges the filtering function and impedance matching function into a single parallel-arm resonator structure. The resonator is designed with resonant frequency frp and anti-resonant frequency fap such that the passband falls within [frp, fap], allowing the same component to provide both bandpass filtering and inductive impedance transformation, thereby reducing overall device complexity and loss.
2Reliability
If a matching resonator is added to reduce matching loss, then impedance matching is improved, but device size increases
Solution Approach 1:
The invention merges the matching resonator function into the existing parallel-arm resonator structure. By designing the parallel-arm resonator with appropriate frequency characteristics (resonant frequency frp ≤ low frequency end of passband and anti-resonant frequency fap ≥ high frequency end of passband), it simultaneously provides filtering and impedance matching functions, eliminating the need for separate matching components and reducing device size.
Solution Approach 2:
The parallel-arm resonator is designed to perform multiple functions: it acts as both the filtering element (providing bandpass characteristics) and the impedance matching element (providing inductive impedance transformation). This multi-functionality reduces the total number of components required and minimizes the overall device footprint.
3Adaptability or versatility
If resonant bandwidth is broadened to improve frequency coverage, then adaptability is improved, but frequency selectivity deteriorates
Solution Approach 1:
The invention changes the frequency parameters of the parallel-arm resonator by adjusting its resonant frequency frp and anti-resonant frequency fap to specific relationships with the passband edges. The resonant frequency is set at or below the low frequency end of the passband, and the anti-resonant frequency is set at or above the high frequency end, creating optimal frequency coverage while maintaining sharp roll-off characteristics through the natural resonance behavior.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration achieves a compact acoustic wave filter with low insertion loss by aligning resonant frequencies and anti-resonant frequencies within the passband, allowing for efficient signal transmission with minimal impedance mismatch and eliminating the need for additional inductive matching circuits.
Implementation Method 1
a first acoustic wave resonator and a second acoustic wave resonator which are formed on an identical piezoelectric substrate
Implementation Method 2
a first resonant frequency which is lower than or equal to a low frequency end of a passband of the acoustic wave filter, and a first anti-resonant frequency which is higher than or equal to a high frequency end of the passband
Data Source
AI summary
An acoustic wave filter includes a serial arm resonator disposed on a serial arm path connecting input/output terminals, and a parallel-arm resonator device connected between the serial arm path and the ground. The serial arm resonator is a first acoustic wave resonator. The parallel-arm resonator device includes a parallel arm resonator and an inductor connected in series between the serial arm path and the ground. The serial arm resonator and the parallel arm resonator are on the same piezoelectric substrate. The resonant frequency of the parallel-arm resonator device is lower than or equal to the low frequency end of the passband of the acoustic wave filter. The anti-resonant frequency of the parallel-arm resonator device is higher than or equal to the high frequency end of the passband.