Switchable Parallel-Arm RF Filter for Low-Frequency Attenuation
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Solution Overview
Problem
Existing high-frequency filter circuits struggle to secure sufficient attenuation in an attenuation band at frequencies lower than the resonant frequency of a parallel arm resonator, limiting their effectiveness in supporting multiple bands.
Innovation Solution
A high-frequency filter circuit configuration that includes a series arm circuit and a parallel arm circuit with a switch-controlled impedance circuit, allowing the impedance of the parallel arm circuit to be switched between conductive and non-conductive states, thereby adjusting the resonant frequency and securing sufficient attenuation at lower frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a basic ladder filter structure with a parallel arm circuit is used, then the filter can support multiple bands through frequency switching, but sufficient attenuation cannot be secured in the attenuation band at frequencies lower than the resonant frequency of the parallel arm resonator
Solution Approach 1:
The parallel arm circuit is segmented into multiple independent branches: a first parallel arm circuit with a first parallel arm resonator, a second parallel arm circuit with a second parallel arm resonator, and a third parallel arm circuit with a third parallel arm resonator. Each branch is controlled by its own switch element, allowing independent frequency switching. This segmentation enables the filter to achieve sufficient attenuation at low frequencies by selectively activating appropriate resonator branches while maintaining multi-band support capability.
2Manufacturing precision
If the resonant frequency of the parallel arm circuit is increased by adding series impedance elements, then the attenuation pole frequency shifts higher, but the ability to provide attenuation at frequencies lower than the original resonant frequency is lost
Solution Approach 1:
The filter employs dynamic switching of parallel arm resonators based on frequency requirements. When operation at frequencies lower than the original resonant frequency is needed, the switch elements activate alternative parallel arm circuits with different resonant frequencies. This dynamic reconfiguration allows the attenuation pole to be positioned appropriately for each operating band, ensuring both precise frequency positioning and comprehensive frequency range coverage.
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 enables the securement of sufficient attenuation at frequencies lower than the resonant frequency of the parallel arm resonator, enhancing the filter's ability to support multiple bands and adjust frequency settings effectively.
Implementation Method 1
elastic wave filters that employ elastic waves have been widely used in band pass filters
Implementation Method 2
bulk acoustic wave (BAW) resonators can be used as the configuration of an elastic wave filter
Data Source
AI summary
A filter (22A) includes: a series arm circuit (11) that is connected between an input/output terminal (22m) and an input/output terminal (22n); and a parallel arm circuit (12) that is connected between a node (x1), which is on a path that connects the input/output terminal (22m) and the input/output terminal (22n), and ground. The parallel arm circuit (12) includes a parallel arm resonator (22p) and an impedance circuit (13) that is serially connected to the parallel arm resonator (22p). The impedance circuit (13) includes a first impedance element, which is one of an inductor and a capacitor, a second impedance element, which is the other of an inductor and a capacitor, and a switch (22SW) that is serially connected to the second impedance element. A first series circuit (14) comprising of the second impedance element and the switch (22SW) is connected in parallel with the first impedance element.