Notch Filter Circuit Using Shifted Shunt Resonators for Broad Isolation
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Solution Overview
Problem
In cellular communications, existing systems face challenges in achieving adequate isolation between different frequency bands in frontend modules without incurring significant additional losses, as current notch filters primarily target specific frequencies and introducing multiple notch filters can enhance series resistance and losses.
Innovation Solution
A notch filter circuit comprising a series of parallel shunt elements, each shifted in frequency to provide multiple stop band frequencies, distributed over a broad notch band, which improves isolation without substantial pole creation in the transfer function, allowing for adjustable isolation by setting proper admittance for each shunt element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple traditional notch filters are introduced to filter out multiple stop band frequencies, then the isolation between different frequency bands is improved, but the series resistance is enhanced thereby producing losses
Solution Approach 1:
The invention divides a single notch filter into multiple parallel shunt elements, each targeting a specific stop band frequency. Instead of using multiple series notch filters that would accumulate resistance, the patent segments the filtering function across parallel branches, thereby maintaining low series resistance while achieving broadstop band rejection across multiple frequency ranges
Solution Approach 2:
The patent merges multiple filtering functions into a single parallel structure where multiple shunt elements operate simultaneously. By combining the admittance effects of multiple parallel resonators, the system achieves the isolation benefits of multiple notch filters without the additive series resistance penalty
2Reliability
If a single notch filter is used to filter out a specific frequency, then the isolation at that specific frequency is improved, but the notch band is limited to a narrow frequency range
Solution Approach 1:
The parallel structure of shunt elements creates a multi-functional notch filter that simultaneously provides stop band rejection at multiple frequencies. Each shunt element contributes its own resonant frequency to the overall transfer function, making the single filter structure universal across a broad frequency spectrum rather than limited to a single frequency point
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 solution enhances isolation across a broad frequency band with minimal additional impedance, achieving improved RX isolation in cellular frontend modules by creating a broader notch band with reduced attenuation, compared to traditional notch filters.
Implementation Method 1
Preferred shunt elements are chosen from resonators operating with acoustic waves
Implementation Method 2
If the band filter is a SAW filter the resonator may be a SAW resonator
Data Source
AI summary
A filter circuit comprises in a signal line a band filter (BF) allowing to let pass a useful frequency band and a notch filter (NF) circuited in series to the band filter for filtering out a stop band frequency. The notch filter comprises a series circuit of a number of parallel shunt elements (SE1 . . . SE6) wherein each shunt element is shifted infrequency against the other shunt elements that the frequencies thereof are distributed (f1 . . . F6) over a notch band. All shunt elements may be realized as a SAW one-port resonator (TRNF) including regions with different pitches.