Acoustic-Wave Filter Circuit Topology for Low-Loss Wideband RF
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Solution Overview
Problem
Designing radio frequency (RF) filters for high-frequency applications, such as above 4 GHz, is challenging due to difficulties in achieving low insertion loss and compact size using conventional bulk acoustic wave (BAW) resonators, and inductors exhibit poor quality factor at high frequencies leading to high losses.
Innovation Solution
A filter circuit design incorporating a BAW resonator with a series LC tank circuit and capacitors, along with optional inductive elements, to achieve low insertion loss and smaller footprint, utilizing equivalent transformations to reduce inductance and capacitance values, allowing for efficient high-frequency filtering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional BAW resonators are used for high-frequency filtering, then filtering function is achieved, but insertion loss increases and device size cannot be reduced
Solution Approach 1:
The patent replaces the conventional BAW resonator's mechanical acoustic wave propagation mechanism with an electrical implementation using LC tank circuits. This substitution eliminates the inherent losses associated with acoustic wave propagation in BAW resonators while maintaining the filtering function through electrical resonance, thereby reducing insertion loss at high frequencies.
Solution Approach 2:
The patent transforms the filtering mechanism by changing the fundamental operating parameters from acoustic frequency and wavelength to electrical resonance frequency and impedance. By using LC tank circuits with carefully selected inductance and capacitance values, the filter achieves the desired frequency response without the insertion loss penalties of conventional BAW resonators.
2Ease of operation
If inductors are used for high-frequency filtering, then filtering is achieved, but quality factor deteriorates leading to high losses
Solution Approach 1:
The patent merges the inductor and capacitor into a unified LC tank circuit configuration where the two components work together to create resonance. This combination allows the circuit to achieve filtering capability through the resonant interaction between L and C, rather than relying on the inductor alone, thereby maintaining quality factor and reducing power loss at high frequencies.
Solution Approach 2:
The capacitor acts as an intermediary element that works with the inductor to create the resonant circuit. By introducing the capacitor as a mediating component, the circuit achieves the desired filtering effect while the capacitor's low loss characteristics help compensate for the inductor's quality factor deterioration at high frequencies.
3Reliability
If acoustic wave resonators are used, then filtering is performed, but device footprint cannot be reduced
Solution Approach 1:
The patent replaces the mechanical acoustic wave resonator structure with an electrical LC tank circuit implementation. This substitution allows the filtering function to be achieved using planar electrical components that occupy significantly less space than acoustic resonators, thereby reducing the device footprint while maintaining filtering reliability.
Solution Approach 2:
The patent creates an electrical equivalent or 'copy' of the acoustic resonator's filtering function using LC tank circuits. By replicating the frequency-selective behavior through electrical resonance rather than acoustic resonance, the design achieves the same filtering reliability with a much smaller physical footprint suitable for integrated circuits.
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 proposed filter circuit achieves low insertion loss and smaller size, enabling efficient high-frequency filtering with reduced power loss and cost, suitable for applications like ultra-wideband technology around 8 GHz.
Implementation Method 1
Using a piezoelectric material as a vibrating medium, acoustic resonators operate by transforming an electrical signal wave that is propagating along an electrical conductor into an acoustic wave that is propagating via the piezoelectric material.
Data Source
AI summary
Certain aspects of the present disclosure provide a filter circuit and techniques for filtering using the filter circuit. The filter circuit generally includes a first filter stage having a first acoustic wave resonator coupled in a series path between a first port of the filter circuit and a second port of the filter circuit, a first inductor-capacitor (LC) tank circuit, a first capacitor coupled between a first terminal of the first acoustic wave resonator and the first LC tank circuit, the first LC tank circuit being coupled between the first capacitor and a reference potential node, and a second capacitor coupled between a second terminal of the first acoustic wave resonator and the first LC tank circuit. In some aspects, the filter circuit includes one or more other filter stages coupled to the first filter stage.