BAW Resonator Filter Blocker Inductors for Wider Bandwidth
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Solution Overview
Problem
BAW resonator filters face challenges in achieving sufficient bandwidth and effective out-of-band rejection, as existing designs often compromise on in-band return loss and passband ripple when trying to expand bandwidth.
Innovation Solution
Incorporating blocker inductors in series between the filter input and output to enhance bandwidth and improve out-of-band frequency rejection, while maintaining in-band performance, by creating sustained low-pass characteristics and reducing gain at higher frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the bandwidth of a BAW resonator filter is expanded, then the filter can accommodate wider frequency ranges, but the in-band return loss and passband ripple performance deteriorates
Solution Approach 1:
A blocker inductor is introduced as an intermediary element in series with the BAW resonator. This inductor acts as a mediator that creates sustained low-pass characteristics above the passband, blocking out-of-band frequencies while leaving the in-band signal path unaffected, thereby resolving the contradiction between bandwidth expansion and in-band performance maintenance
2Device complexity
If conventional filter designs are used, then the structure is simple, but the out-of-band frequency rejection is insufficient
Solution Approach 1:
The blocker inductor serves as an intermediary component that specifically targets and blocks out-of-band frequencies. By placing this inductor in series, it creates a low-pass effect that rejects frequencies above the passband without requiring complex multi-resonator structures, thus improving rejection performance with minimal added complexity
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
The use of blocker inductors expands the filter bandwidth without compromising in-band return loss or passband ripple, significantly improving out-of-band rejection and insertion loss, particularly relevant for demanding applications like CDMA filters.
Implementation Method 1
A BAW resonator comprises a piezoelectric material that is placed between two electrodes. The resonant behavior of a BAW resonator is a result of the conversion of electrical energy to acoustic energy, and the propagation of the acoustic energy across the piezoelectric material within the BAW.
Implementation Method 2
This out-of-band rejection is improved by utilizing the parasitic capacitance ('Cp') of the corresponding BAW resonator above its parallel resonant frequency ('Fp') and may constitute a third shorting or series resonance above the passband defined at: F=1/(2Π*SQRT(Cp*Lhelper))
Data Source
AI summary
Embodiments of the present invention provide systems, devices and methods for improving both the bandwidth of a BAW resonator bandpass filter and the suppression of out-of-band frequencies above the passband. In various embodiments of the invention, blocker inductors are located in series between the filter input and the filter output to realize both bandwidth enhancement and improved out-of-band frequency rejection. For example, a first blocker inductor may be located at the input and a second blocker inductor may be located at the output of a BAW resonator bandpass filter.