Multiplexer Series-Arm Resonators for Higher-Band Loss Reduction
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Solution Overview
Problem
Existing multiplexers for mobile communication terminals face challenges in minimizing loss in the pass band of filters with higher frequency bands due to bulk wave radiation in acoustic wave resonators, leading to deteriorated performance.
Innovation Solution
A multiplexer design that includes a common terminal connected to both a first acoustic wave filter with a lower pass band and a second filter with a higher pass band, utilizing a series arm circuit with a first series arm resonator and a second series arm resonator connected in parallel, where the second resonator's resonant frequency is on the higher frequency side, reducing bulk wave loss by distributing power between the resonators and adjusting impedance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single acoustic wave resonator is used in the series arm circuit, then the filter configuration is simple, but bulk wave loss occurs in frequency bands higher than the anti-resonant frequency, deteriorating the pass band loss of higher frequency filters
Solution Approach 1:
The series arm circuit is segmented into multiple resonators (first series arm resonator and second series arm resonator) with different resonant frequencies. The first resonator handles lower frequency signals while the second resonator handles higher frequency signals, preventing bulk wave loss from affecting the pass band of higher frequency filters. This segmentation allows each resonator to operate in its optimal frequency range without causing harmful effects to other frequency bands.
2Loss of energy
If multiple resonators are added to reduce bulk wave loss, then pass band loss of higher frequency filters is improved, but the device complexity increases
Solution Approach 1:
Each resonator in the series arm circuit is assigned a specific resonant frequency tailored to its intended frequency band. The first series arm resonator has a resonant frequency suited for lower bands, while the second series arm resonator has a resonant frequency suited for higher bands. This local optimization ensures that each component performs best in its designated frequency range, reducing overall system loss without requiring all resonators to be identical or overly complex.
3Loss of energy
If the resonant frequency of the second series arm resonator is set within the pass band of the first filter, then power distribution helps reduce bulk wave loss, but it may cause interference with the first filter's pass band
Solution Approach 1:
The resonant frequency of the second series arm resonator is carefully selected to be within the pass band of the first filter, but this parameter is optimized so that the resonator's primary function is to reduce bulk wave loss in higher frequency bands. The resonant frequency positioning allows the second resonator to effectively counteract bulk wave effects without creating significant interference in the first filter's pass band, as the power distribution and impedance characteristics are tuned to minimize harmful interactions.
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 effectively reduces bulk wave loss in the pass band of the second filter, enhancing the multiplexer's performance by minimizing loss and improving impedance matching, thereby reducing return loss and improving filter steepness.
Implementation Method 1
a frequency at which an impedance of a resonator is locally minimum is defined as a resonant frequency, and a frequency at which an impedance of the resonator is locally maximum is defined as an anti-resonant frequency
Implementation Method 2
there is a loss due to bulk wave radiation (hereinafter referred to as a 'bulk wave loss') in a frequency band higher than the anti-resonant frequency
Data Source
AI summary
A multiplexer includes first and second filters connected to a common terminal. The second filter has a pass band on a higher frequency side with respect to a pass band of the first filter. The first filter includes a series arm circuit, and a parallel arm circuit having a resonant frequency on a lower frequency side with respect to a frequency at a low frequency end of a pass band of the first filter, and the series arm circuit includes a series arm resonator having a resonant frequency in the pass band of the first filter and a series arm resonator that is electrically connected in parallel to the series arm resonator and that has a resonant frequency on a higher frequency side with respect to a frequency at a high frequency end of the pass band of the first filter.