Electronically Tunable Notch Filter for Multi-Band RF Isolation
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Solution Overview
Problem
The increasing number of operating bands in modern wireless communications standards leads to complexity and size issues in RF front-end circuitry for devices using carrier aggregation and MIMO configurations, primarily due to the need for specialized filtering circuitry that is not efficiently compacted.
Innovation Solution
A tunable notch filter is introduced, featuring a series connection of acoustic resonators and inductive elements with electronically tunable capacitors, providing a highly selective notch filter response to attenuate undesired frequencies effectively, thereby reducing the complexity and size of the filtering circuitry.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional acoustic filters are used for each operating band, then signal isolation between bands is achieved, but the filtering circuitry complexity and size increase significantly
Solution Approach 1:
The patent implements a single notch filter circuit that can be electronically reconfigured to provide filtering for multiple different operating bands. By using voltage-controlled capacitors that can be tuned to different capacitance values, the same physical filter circuit serves multiple filtering functions that would traditionally require separate dedicated filters for each band, thereby reducing overall circuit complexity while maintaining signal isolation across all bands
Solution Approach 2:
The patent employs dynamically tunable capacitors whose capacitance values can be changed electronically via control voltages. This dynamic reconfigurability allows the filter's resonant frequency and notch position to be adjusted on-the-fly to match different operating bands, enabling a single static physical structure to adapt and perform multiple filtering roles that would otherwise require multiple fixed filters
2Area of stationary object
If multiple acoustic filters are grouped into RF multiplexers, then area is reduced, but filtering performance and selectivity may be compromised
Solution Approach 1:
The patent uses voltage-controlled capacitors that allow precise electronic adjustment of the filter's electrical parameters (capacitance values) to optimize filtering performance for different bands. This parameter tuning capability compensates for the potential performance degradation from integration, enabling the compact multiplexer design to achieve the same high selectivity and attenuation performance as larger distributed filter arrangements by precisely controlling the electrical characteristics of the shared filter components
3Reliability
If specialized filtering circuitry is added for each operating band, then band separation is achieved, but the overall device size increases
Solution Approach 1:
The patent implements a single notch filter circuit that can be electronically reconfigured to provide filtering for multiple different operating bands. By using voltage-controlled capacitors that can be tuned to different capacitance values, the same physical filter circuit serves multiple filtering functions that would traditionally require separate dedicated filters for each band, thereby reducing overall circuit complexity while maintaining signal isolation across all bands
Solution Approach 2:
The patent merges multiple filtering functions into a single integrated notch filter circuit. Instead of having separate physical filters for each operating band, the design combines them into one shared filter structure with common components (inductors, capacitors, resistors) that are electronically reconfigured through switching and capacitance tuning to provide band-specific filtering, thus consolidating what would be multiple discrete components into a compact unified circuit
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 tunable notch filter achieves significant attenuation of undesired frequencies while minimizing insertion loss, thereby enhancing the performance and reducing the size and complexity of RF front-end circuitry, addressing the challenges posed by multiple operating bands.
Implementation Method 1
a first acoustic resonator coupled in series with a first inductive element between a filter input node and a filter output node
Data Source
AI summary
A tunable notch filter is disclosed with a first acoustic resonator coupled in series with a first inductive element between a filter input node and a filter output node. A first capacitor is coupled in parallel with the first acoustic resonator and the first inductive element. In at least one embodiment, the first capacitor is configured to have variable capacitance that is electronically tunable by way of an electronic controller. A second acoustic resonator is coupled in series with a second inductive element between the filter output node and a signal ground node. A second capacitor is coupled in parallel with the second inductive element. In at least one embodiment, the second capacitor is electronically tunable. The tunable notch filter is configured to provide a highly selective notch filter response between the filter input node and the filter output node with high attenuation.