Ladder Filter Circuit Layout for Low Pass-Band Loss
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Solution Overview
Problem
Ladder filter circuits in mobile communication devices face challenges in achieving low input loss in the pass band while maintaining steep attenuation characteristics, as the addition of inductors shifts resonant frequencies and reduces attenuation steepness, and increasing the number of parallel arm resonators increases input loss in the pass band.
Innovation Solution
A filter device with a configuration of series arm resonators, parallel arm resonators, and inductors, where a first inductor with the highest inductance is connected in series with a parallel arm resonator having the highest anti-resonant frequency, and other parallel arm resonators are connected to different ground terminals, maintaining steep attenuation characteristics while reducing input loss in the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an inductor is connected in series with a parallel arm resonator, then the input loss in the pass band is reduced, but the resonant frequency is shifted to a lower-frequency side and the steepness of attenuation characteristics is lost
Solution Approach 1:
The patent changes the connection configuration parameter of the inductor from series connection to parallel connection with the parallel arm resonator. This parameter change allows the inductor to provide its loss-reduction benefit without causing the resonant frequency shift that occurs with series connection, thereby maintaining both low input loss and steep attenuation characteristics.
Solution Approach 2:
The patent introduces a separate inductor component that copies the loss-reduction function needed in the circuit, but implements it through a different connection topology (parallel rather than series). This copied function achieves the desired effect without the harmful side effects of the original series connection approach.
2Ease of manufacture
If many parallel arm resonators are added in a ladder filter circuit, then the attenuation characteristics in the attenuation band are improved, but the input loss in the pass band is increased
Solution Approach 1:
The patent introduces inductors as intermediary elements that mediate between the parallel arm resonators and the ground connections. These inductors act as impedance transformation elements that allow the parallel arm resonators to provide steep attenuation characteristics while the inductors compensate for the increased input loss by providing additional reactance control in the pass band.
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 configuration significantly reduces input loss in the pass band while maintaining steep attenuation characteristics, improving frequency characteristics by adjusting the connection of inductors and resonators, specifically by keeping anti-resonant frequencies intact and shifting resonant frequencies to lower frequencies.
Implementation Method 1
a ladder filter circuit including a series arm resonator, a parallel arm resonator, and an inductor connected in series with the parallel arm resonator
Implementation Method 2
A first inductor having a highest inductance of the inductors is electrically connected in series with a first parallel arm resonator having a highest anti-resonant frequency
Data Source
AI summary
A filter device includes series and parallel arm resonators provided at a filter chip and inductors electrically connected in series with respective ones of the parallel arm resonators. A first inductor having the highest inductance of the inductors is electrically connected in series with a first parallel arm resonator having the highest anti-resonant frequency of the parallel arm resonators. One end of the first parallel arm resonator and one end of a second parallel arm resonator in other ones of the parallel arm resonators are electrically connected to a same wiring line in wiring lines separated by the series arm resonators on a line electrically connecting an input terminal and an output terminal of the filter chip. The other ends of the first and second parallel arm resonators are respectively electrically connected to first and second ground terminals of the filter chip.