Integrated SAW Band-Pass and Band-Stop Filter for Channel Selectivity
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Solution Overview
Problem
Existing surface acoustic wave filters face challenges in achieving improved adjacent channel selectivity and remote channel selectivity, particularly in high-frequency applications such as mobile communications, where they struggle to effectively suppress interfering signals and noise within narrow bandwidths.
Innovation Solution
The design incorporates a band-stop filter with electroacoustic series and parallel elements, where the resonance and anti-resonance frequencies of these elements are strategically positioned outside the passband of the band-pass filter, utilizing SAW or BAW transducers and resonators to create a filter with low insertion loss and significant signal suppression, achieving improved selectivity and noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a band-stop filter with series and parallel elements is added to improve selectivity, then adjacent channel selectivity and remote channel selectivity are improved, but device complexity increases
Solution Approach 1:
The patent combines the band-pass filter and band-stop filter into a single integrated filter device, where the series elements and parallel elements of the band-stop filter are merged with the transducers of the band-pass filter. This integration allows both filtering functions to be achieved within one unified structure, improving channel selectivity while controlling device complexity through shared components and acoustic wave paths.
Solution Approach 2:
The filter device performs multiple functions simultaneously: it acts as both a band-pass filter for the desired signal frequency and a band-stop filter for suppressing adjacent and remote channels. The series and parallel electroacoustic elements serve dual purposes by providing both signal transmission in the passband and signal attenuation in the stopband, thereby improving selectivity without proportionally increasing complexity.
2Object-affected harmful factors
If the resonance and anti-resonance frequencies are positioned outside the passband to improve suppression, then interfering signal suppression is improved, but insertion loss in the passband may increase
Solution Approach 1:
The patent carefully adjusts the resonance and anti-resonance frequencies of the series and parallel elements to specific positions outside the passband. By optimizing these frequency parameters, the filter achieves maximum suppression of interfering signals (at least 50 dB) while minimizing the impact on the passband. The series elements have resonance frequencies below the passband and anti-resonance frequencies above it, creating a stopband that effectively suppresses adjacent and remote channels without significantly affecting passband transmission.
3Manufacturing precision
If a narrow stopband is used to improve selectivity, then channel selectivity is improved, but bandwidth for useful signals is reduced
Solution Approach 1:
The filter exhibits different characteristics in different frequency regions: in the passband region, it provides low attenuation for useful signals with a relatively broad bandwidth; in the stopband region, it provides high attenuation (at least 50 dB) for interfering signals with a narrow bandwidth. This local differentiation of filter properties allows simultaneous achievement of broad passband and narrow stopband, resolving the contradiction between selectivity and bandwidth.
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 results in a filter with enhanced adjacent and remote channel selectivity, providing at least 50 dB of suppression for interfering signals while maintaining low insertion loss, effectively addressing the limitations of previous filters in high-frequency applications.
Implementation Method 1
Surface acoustic wave filter comprising a band-pass filter and a band-stop filter
Implementation Method 2
track with acoustically coupled electroacoustic transducers
Implementation Method 3
In at least one of the electroacoustic elements of the band-stop filter, the resonance frequency and the anti-resonance frequency lie outside the passband of the band-pass filter
Implementation Method 4
band-stop filter with at least one electroacoustic series element and at least one electroacoustic parallel element
Data Source
AI summary
An electric filter has a band-pass filter that includes a track with acoustically coupled electroacoustic transducers. The filter includes a band-stop filter with at least one electroacoustic series element and at least one electroacoustic parallel element. The series element of the band-stop filter is connected in series to at least one of the transducers of the band-pass filter. The parallel element of the band-stop filter is arranged in a shunt arm that is electrically connected to at least one of the transducers of the band-pass filter. In at least one of the electroacoustic elements of the band-stop filter, the resonance frequency and the anti-resonance frequency lie outside the passband of the band-pass filter.