BAW Band-Pass Filter Circuit Using Identical Resonators
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Solution Overview
Problem
The manufacturing of band pass filters using acoustic resonators is challenging due to the need for precise, slightly shifted resonator characteristics, which requires complex and costly processes, and existing solutions either compromise on filter performance or increase manufacturing complexity.
Innovation Solution
A band pass filtering circuit is designed with two identical BAW resonators and capacitors, where one resonator and its associated capacitor form a serial branch, and another identical resonator and capacitor form a parallel branch, allowing for easier integration and manufacturing by ensuring resonance and anti-resonance frequencies are perfectly compensated.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two acoustic resonators with slightly shifted characteristics are assembled in serial/parallel to form a band pass filter, then a narrow band pass filter with powerful filtering performance is achieved, but the manufacturing process becomes particularly delicate and expensive due to the need for high precision in resonator characteristics
Solution Approach 1:
The patent changes the approach from adjusting resonator characteristics to using identical resonators with fixed characteristics, and instead adjusts the capacitor values to achieve the desired frequency shift. This parameter substitution simplifies manufacturing by eliminating the need for precise resonator characterization control.
Solution Approach 2:
Instead of shifting resonator characteristics to create the band pass filter, the invention inverts the approach by using identical resonators and shifting the capacitor values. This reversal of the traditional design methodology resolves the manufacturing precision issue while maintaining filtering performance.
2Measurement precision
If laser trimming is applied to shift resonator frequencies after passivation, then frequency adjustment is achieved, but individual resonator correction is not possible due to the broad laser beam, allowing only uniform correction of the resonator set
Solution Approach 1:
The patent extracts the frequency adjustment function from the resonators and transfers it to the capacitors. This separation allows independent adjustment of capacitor values without affecting resonator characteristics, eliminating the need for complex laser trimming processes and enabling precise individual adjustment.
3Ease of manufacture
If BAW resonators are used to enable thorough integration of filtering circuits in semiconductor products, then manufacturing costs are reduced, but the need for precise resonator characteristics and complex manufacturing steps remains
Solution Approach 1:
The patent changes which parameters require precision control: instead of requiring precise resonator characteristics, the invention requires precise capacitor values. Since capacitors are easier to manufacture with high precision in semiconductor processes, this parameter swap enables better integration while maintaining manufacturing simplicity.
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 approach simplifies the manufacturing process and achieves a powerful band pass filter with an appropriate profile, facilitating easier integration into semiconductor products and reducing manufacturing costs while maintaining desired filtering characteristics.
Implementation Method 1
Acoustic resonators are today very widespread in applications for the general public but also in professional applications because of their efficiency, in particular for the realization of very powerful band-pass filters
Implementation Method 2
Researches have been made on two types of acoustic resonators which present remarkable performances, namely the resonators of type SAW (Surface Acoustic Wave Resonator)
Implementation Method 3
those of type BAW (Bulk Acoustic Wave Resonator). In the first type, the acoustic resonator is positioned on the surface of a semiconductor product while, in the second type, it is positioned inside a volume delimited between a lower electrode and a higher electrode so that the acoustic wave develops in that same volume
Implementation Method 4
allowing for easier integration and manufacturing by ensuring resonance and anti-resonance frequencies are perfectly compensated
Data Source
AI summary
A band pass filtering circuit based on a quadripole includes a serial branch having a first acoustic resonator presenting a frequency of resonance and a frequency of anti-resonance and mounted in serial with a first capacitor; a parallel branch having a second acoustic resonator resulting from the same manufacturing process as the first resonator and mounted in parallel with a second capacitor of identical value to that the first capacitor. The filtering circuit is particularly but not exclusively adapted to the realization of integrated filtering circuits used in mobile telephony.