Multiplexer Filter Ladder Using Elastic Wave Resonators
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Solution Overview
Problem
Filters in multiplexers face challenges in achieving a wide pass band with steep attenuation characteristics at the ends and small insertion loss, particularly in LC filters and elastic wave filters, due to difficulties in realizing both flat bandpass characteristics in a wide frequency band and steep attenuation at the frequency band edges.
Innovation Solution
A filter configuration using a series circuit with a series arm resonator and a parallel arm resonator connected in a ladder form, where both are formed using elastic wave resonators, allowing for steep attenuation characteristics at the pass band edges and functioning as a low pass filter with reduced insertion loss by becoming inductive in the pass band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If LC filters are used in multiplexers, then the filter structure is simple and easy to manufacture, but the attenuation characteristics at the ends of the pass band are not steep
Solution Approach 1:
The patent combines LC filter structures with elastic wave resonators to create a hybrid filter system. The series circuit includes both an inductor and a series arm resonator (elastic wave type), while parallel arm resonators are connected in parallel. This merging allows the filter to inherit the simplicity of LC structures while gaining the steep attenuation characteristics of elastic wave resonators at the pass band edges.
2Manufacturing precision
If elastic wave filters are used to achieve steep attenuation characteristics, then the attenuation at the frequency band edges improves, but the insertion loss increases and matching becomes difficult
Solution Approach 1:
The patent carefully controls the electrical parameters of the elastic wave resonators, specifically setting the resonant frequencies and anti-resonant frequencies to specific values relative to the pass band edges. The series arm resonator has its anti-resonant frequency at or above the higher frequency end of the pass band, while parallel arm resonators have resonant frequencies above the pass band. This parameter optimization ensures steep attenuation without excessive insertion loss.
Solution Approach 2:
The filter applies different circuit configurations at different locations: series arm resonators are placed in the series circuit path to provide attenuation at the pass band edges, while parallel arm resonators are connected in parallel to ground to provide additional attenuation without affecting the main signal path impedance. This localized application of resonators minimizes overall insertion loss while achieving the required attenuation characteristics.
3Adaptability or versatility
If the pass band is widened to accommodate new frequency bands, then the frequency band coverage improves, but the attenuation characteristics at the ends of the pass band become less steep
Solution Approach 1:
The filter is segmented into multiple resonant circuits with different functions: series arm resonators for attenuation at the higher frequency end, parallel arm resonators for additional attenuation and impedance control, and LC components for overall pass band shaping. Each segment is optimized for its specific frequency range, allowing the total pass band to be widened while maintaining steep attenuation at each edge through the coordinated action of different segments.
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 filters with a wide pass band and steep attenuation characteristics at the ends while minimizing insertion loss, suitable for multiplexers requiring carrier aggregation across different frequency bands.
Implementation Method 1
By forming each of the series arm resonator and the parallel arm resonator using an elastic wave resonator, steep attenuation characteristics at the ends of the pass band, which are typical characteristics of ladder elastic wave filters, can be obtained on the basis of an attenuation pole formed by the anti-resonance of the series arm resonator
Implementation Method 2
The series circuit becomes inductive in the pass band. Since the series circuit becomes inductive in the pass band, the filter functions as a low pass filter including an LC filter in the pass band
Data Source
AI summary
A filter having a pass band includes a series circuit in which a series arm resonator and a first inductor are connected in series with each other and which forms at least part of a signal path R connecting a first input/output terminal and a second input/output terminal and a parallel arm resonator connected between one end of the series circuit and a ground. The series circuit becomes inductive in the pass band. An anti-resonant frequency of the series arm resonator is higher than a frequency at a higher-frequency end of the pass band. A resonant frequency of the parallel arm resonator is higher than the anti-resonant frequency of the series arm resonator.