Hybrid Multiplexer Filter Layout for Closely Spaced RF Bands
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Solution Overview
Problem
Existing multiplexers face difficulties in demultiplexing or multiplexing high-frequency signals with frequency bands that are close to each other due to limitations in steep attenuation characteristics of LC filters and the inability to achieve flat bandpass characteristics over a wide band with acoustic wave filters.
Innovation Solution
A multiplexer design incorporating a second filter with a matching circuit, a low pass filter, and a high pass filter, where the filters are cascade connected and include acoustic wave resonators, providing steep attenuation and reduced loss over a wide band by adjusting the resonant and anti-resonant frequencies of the resonators to create attenuation poles within the desired frequency band.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If an LC filter is used in the multiplexer, then the device complexity is reduced and ease of manufacture is improved, but the attenuation characteristics become insufficient and the ability to demultiplex close frequency bands deteriorates
Solution Approach 1:
The multiplexer is divided into multiple filters (first filter and second filter), each responsible for specific frequency bands. The second filter is further segmented into a low pass filter and a high pass filter connected in parallel, allowing each segment to specialize in attenuating specific frequency ranges, thereby achieving steep attenuation characteristics while maintaining manufacturing feasibility
Solution Approach 2:
The invention changes the electrical parameters of the filters by configuring the low pass filter with a cutoff frequency and the high pass filter with a cutoff frequency such that their combined attenuation characteristics create steep roll-off. The resonant frequencies and impedance values are specifically adjusted to achieve the desired attenuation performance
2Reliability
If an acoustic wave filter is used to achieve steep attenuation characteristics, then the ability to demultiplex close frequency bands is improved, but the bandpass characteristic becomes non-flat and insertion loss increases over wide bands
Solution Approach 1:
The invention merges a low pass filter and a high pass filter in parallel configuration within the second filter. This combination allows the low pass filter to handle attenuation of frequencies above its cutoff while the high pass filter handles frequencies below its cutoff, achieving steep attenuation characteristics without the excessive insertion loss that would result from using a single acoustic wave filter
Solution Approach 2:
The second filter serves multiple functions simultaneously: it provides steep attenuation characteristics through the parallel LC filters, maintains flat bandpass characteristics over wide bands by appropriate cutoff frequency selection, and enables demultiplexing of close frequency bands. This multi-functionality eliminates the need to choose between different filter types
3Adaptability or versatility
If the frequency bands are made close to each other to increase multi-band capability, then the adaptability is improved, but the difficulty of demultiplexing and multiplexing increases due to insufficient attenuation
Solution Approach 1:
The frequency spectrum is segmented into distinct bands handled by different filters. The second filter is segmented into low pass and high pass components that together provide the steep attenuation needed to separate closely spaced frequency bands, making demultiplexing feasible even when bands are close together
Solution Approach 2:
The cutoff frequencies of the low pass filter and high pass filter are specifically adjusted based on the frequency bands to be demultiplexed. By changing these parameter values, the multiplexer can adapt to different frequency band configurations while maintaining the ability to achieve sufficient attenuation between close 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 solution enables effective demultiplexing or multiplexing of high-frequency signals with wide and closely spaced frequency bands, reducing leakage and insertion loss while maintaining low impedance over a wide band, thus improving demultiplexing and multiplexing characteristics.
Implementation Method 1
a resonant frequency of the first parallel arm resonator and an anti-resonant frequency of the first serial arm resonator are both located between a frequency at a low-band end of the first frequency band and a frequency at a high-band end of the first frequency band
Implementation Method 2
the low pass filter includes a first inductor provided on a signal path connecting a first terminal and a second terminal of the second filter, and a first parallel arm resonator which is an acoustic wave resonator connected between a node on the signal path and a ground
Data Source
AI summary
A hybrid multiplexer includes a filter configured to allow a high-frequency signal of an HB to pass therethrough, and a filter configured to allow a high-frequency signal of an MB to pass therethrough, in which the filter includes a matching circuit, a first resonance circuit defined by one of an LPF and an HPF, and a second resonance circuit defined by the other of the LPF and the HPF, the LPF includes an inductor and a parallel arm resonator, the HPF includes a serial arm resonator and an inductor, and a resonant frequency of the parallel arm resonator and an anti-resonant frequency of the serial arm resonator are both located between a frequency at a low-band end of the HB and a frequency at a high-band end of the HB.