Multi-Path RF Filter Using Impedance Cancellation for Wide 5G Passbands
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Solution Overview
Problem
Current filter designs face challenges in achieving wide bandwidth and high out-of-band rejection, particularly in 5G frequency bands, due to limitations in electromechanical coupling coefficients of BAW resonators, leading to high insertion loss and difficulty in meeting stringent intermodulation distortion specifications.
Innovation Solution
A multi-path filter design incorporating a band pass section and an extractor section with series and shunt acoustic wave resonators, along with a phase shifter, which combines impedance responses to create a wide passband and significant rejection, overcoming the limitations of BAW resonators by achieving impedance cancellation outside the passband.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of moving object
If acoustic wave ladder filters are used to achieve wide passbands, then bandwidth is improved, but out-of-band rejection deteriorates
Solution Approach 1:
The filter is divided into multiple parallel signal paths (first signal path with series resonator, second signal path with shunt resonator and phase shifter) that process signals differently and combine their responses to achieve both wide bandwidth and high rejection
Solution Approach 2:
The filter combines different types of acoustic wave resonators (series and shunt resonators) with different impedance characteristics to create a composite structure that achieves both wide passband and high out-of-band rejection
2Device complexity
If BAW resonators with limited electromechanical coupling coefficients are used, then device complexity is reduced, but bandwidth is limited
Solution Approach 1:
The filter uses dynamic phase shifting in the second signal path to adjust the combined impedance response, enabling the system to achieve bandwidth exceeding the limitations of individual BAW resonators while maintaining a relatively simple resonator configuration
3Object-affected harmful factors
If traditional ladder filter designs are used to achieve high rejection, then out-of-band rejection is improved, but insertion loss increases
Solution Approach 1:
The filter uses a shunt resonator that is intentionally over-coupled or tuned to a frequency slightly offset from the passband edge, creating strong rejection with minimal impact on passband insertion loss
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 multi-path filter design provides a bandwidth exceeding the BAW resonator's electromechanical coupling coefficient limit, achieving wide passbands and high rejection at frequencies where ladder designs struggle, with comparable filter loss and lower resonator counts, thus meeting demanding 5G specifications.
Implementation Method 1
In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 2
BAW filters include BAW resonators. Example BAW resonators include film bulk acoustic wave resonators (FBARs) and BAW solidly mounted resonators (SMRs). In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer
Implementation Method 3
The phase shifter can include a transmission line and a capacitor
Implementation Method 4
Impedances of the first signal path and the second signal path can cancel each other outside of the passband to form rejections
Data Source
AI summary
Aspects of this disclosure relate to a multi-path filter for filtering a radio frequency signal. The multi-path filter includes a band pass section and an extractor section. The band pass section including a series acoustic wave resonator. The extractor section includes a second acoustic wave resonator and a phase shifter. The multi-path filter has a passband formed by at least a combined impedance response of the band pass section and the extractor section. The multi-path filter has a rejection band outside the passband that is formed by at least cancellation of impedance responses of the band pass section and the extractor section. Related multiplexers, radio frequency modules, radio frequency systems, wireless communication devices, and methods are disclosed.