Ladder Filter Circuit with Series Third Resonators
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Solution Overview
Problem
Existing filter circuits in radio communication devices, such as cellular phones, have limited improvement potential in cut-off characteristics on the lower-frequency side of the pass band due to fixed anti-resonant frequencies of resonators.
Innovation Solution
Incorporating a series of third resonators with lower anti-resonant frequencies and smaller combined capacitance than second resonators, connected in series and parallel with first resonators in a ladder filter circuit, to enhance cut-off characteristics on the lower-frequency side.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the anti-resonant frequency of the third resonator is fixed to the anti-resonant frequency of the second resonator, then the filter circuit achieves basic cut-off characteristics, but the cut-off characteristics on the lower-frequency side of the pass band cannot be significantly improved
Solution Approach 1:
The patent changes the anti-resonant frequency parameter of the third resonator to be lower than that of the second resonator. This parameter change enables the third resonator to provide additional cut-off characteristics on the lower-frequency side of the pass band, significantly improving the overall filter performance without affecting the existing higher-frequency cut-off characteristics.
2Adaptability or versatility
If a third resonator is added to the series arm in parallel with the first resonator, then the effective use of frequency band is improved, but the device complexity increases
Solution Approach 1:
The patent merges the third resonator into the existing ladder filter structure by connecting it in parallel with the first resonator in the series arm. This merging approach allows the third resonator to contribute to the cut-off characteristics on the lower-frequency side while maintaining the overall ladder filter architecture, thus improving frequency band utilization without drastically increasing structural complexity.
3Reliability
If the combined capacitance of the third resonators is made smaller than the electrostatic capacitance of the second resonators, then the Q values are increased for better signal reflection prevention, but the impedance matching becomes more difficult
Solution Approach 1:
The patent sets the combined capacitance of the third resonators to be smaller than the electrostatic capacitance of the second resonators. This capacitance parameter change increases the Q values of the third resonators, enhancing their ability to prevent signal reflection at the lower-frequency cut-off point. The impedance matching is achieved through careful selection of the capacitance values to maintain compatibility with the overall filter design.
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
Significantly improved cut-off characteristics on the lower-frequency side of the pass band, with sharper filtering and increased Q values of the third resonators compared to second resonators, ensuring better impedance matching and signal reflection prevention.
Implementation Method 1
a plurality of first resonators provided in a series arm, a plurality of second resonators provided in a parallel arm, and at least one or more third resonators that are electrically connected in series with each other and are electrically connected in parallel with the first resonators in the series arm
Implementation Method 2
An anti-resonant frequency of the third resonators is lower than an anti-resonant frequency of the second resonators
Data Source
AI summary
A filter circuit includes a plurality of first resonators provided in a series arm, a plurality of second resonators provided in a parallel arm, and at least one or more third resonators that are electrically connected in series with each other and are electrically connected in parallel with the first resonators in the series arm. An anti-resonant frequency of the third resonators is lower than an anti-resonant frequency of the second resonators. A combined capacitance of the at least one or more third resonators electrically connected in series with each other is smaller than an electrostatic capacitance of the second resonators.