Variable Frequency Filter Topology for Lower-Side Attenuation
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Solution Overview
Problem
Existing variable frequency filters struggle to achieve sufficient attenuation at the lower-frequency side of the passband, particularly when multiple communication bands such as 3GPP and digital television bands are closely aligned, due to a steep slope at the higher-frequency attenuation pole and limited attenuation at the lower-frequency pole, making it difficult to achieve a wide bandwidth and comply with spurious emission regulations.
Innovation Solution
A variable frequency filter design incorporating a ladder resonance circuit, a first attenuation circuit with a switchable second parallel arm resonator, and a second attenuation circuit with a switchable capacitor, allowing for adjustable attenuation poles and extended passband coverage to satisfy multiple communication frequency bands and spurious emission regulations, while maintaining a steep slope at the higher-frequency attenuation pole.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If capacitors are used to form attenuation poles in a ladder filter with BAW resonators, then the second attenuation pole (higher frequency side) achieves a steep slope, but the first attenuation pole (lower frequency side) has only a small amount of attenuation
Solution Approach 1:
The patent changes the configuration parameters of the attenuation circuits by introducing different circuit topologies (series RC circuit for first attenuation pole, parallel RC circuit for second attenuation pole) to achieve different attenuation characteristics at each pole, thereby resolving the contradiction between steep slope requirement and sufficient attenuation requirement
Solution Approach 2:
The patent applies different circuit configurations to different locations (attenuation poles) based on their specific requirements: the first attenuation pole uses a series RC circuit for sufficient attenuation, while the second attenuation pole uses a parallel RC circuit for steep slope,实现ing localized optimization of attenuation characteristics
2Device complexity
If a conventional variable frequency filter is used, then the structure is simple, but the bandwidth of stopband is narrow and the amount of attenuation on the lower-frequency side is insufficient
Solution Approach 1:
The patent segments the attenuation function into two separate attenuation circuits (first and second attenuation circuits) with different configurations, allowing each circuit to be optimized for its specific function: one for sufficient attenuation and another for steep slope, thereby achieving both wide stopband bandwidth and high attenuation while maintaining reasonable structural complexity
3Adaptability or versatility
If the passband is extended to cover multiple communication bands, then the filter can handle multiple bands (3GPP, digital television, Wi-Fi), but the attenuation at the lower-frequency side becomes insufficient
Solution Approach 1:
The patent uses switchable components (switches connected to capacitors and resistors) to change the circuit parameters dynamically, allowing the filter to maintain sufficient attenuation at the lower-frequency side while extending the passband to cover multiple communication bands including 3GPP, digital television, and Wi-Fi bands
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 design effectively increases attenuation at the lower-frequency side, ensures compliance with spurious emission regulations, and provides a wide bandwidth, enabling efficient filtering across multiple communication bands with reduced unnecessary wave components, thus enhancing the performance and miniaturization of communication terminals.
Implementation Method 1
a parallel arm circuit that is connected between a node and ground and that includes at least one parallel arm resonator
Implementation Method 2
ladder filter constituted by bulk acoustic wave (BAW) resonators
Data Source
AI summary
A first attenuation circuit is connected between a node and ground, and the node is located between a ladder resonance circuit and a transmitter-side terminal. A second attenuation circuit is connected between a first parallel arm resonator of the ladder resonance circuit and ground and is connected in series to the first parallel arm resonator. The first attenuation circuit includes a second parallel arm resonator and a first switch that switches between a first state in which the second parallel arm resonator is connected to the node and a second state in which the first switch is open. The second attenuation circuit includes a capacitor and a second switch that switches between a first state in which the capacitor is connected to the first parallel arm resonator and a second state in which the first parallel arm resonator is connected to ground.