Balanced Lattice Filter Circuit for Steep Cut-Off With Fewer Elements
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Solution Overview
Problem
Conventional filter devices using a ladder structure for high pass or low pass filters in communication equipment have unbalanced input and output, requiring a large number of elements to achieve a steep cut-off characteristic, especially when dealing with frequency bands close to each other like TV and mobile telephone signals in the VHF/UHF and 800 MHz/1.8 GHz bands.
Innovation Solution
A lattice-type filter circuit with balanced signal terminals and resonators, where resonant circuits are connected in series or parallel arms between input and output terminals, allowing for balanced input and output with a reduced number of elements and achieving a steep cut-off characteristic by varying the frequency characteristics of resonators and impedance elements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ladder type structure is used to realize high pass or low pass filter, then the filter can be constructed with series resonant circuits and impedance elements, but the input and output become unbalanced and the number of elements increases
Solution Approach 1:
The filter is divided into multiple unit filters, each consisting of a series resonant circuit and an impedance element. These unit filters are connected in cascade to achieve the desired steep cut-off characteristic while maintaining a manageable structure for manufacturing.
Solution Approach 2:
The patent introduces a balanced-to-unbalanced conversion circuit at the input and a unbalanced-to-balanced conversion circuit at the output. This asymmetric configuration allows the filter to process balanced signals while internally using the simpler ladder structure, thus resolving the contradiction between ease of manufacture and device complexity.
2Manufacturing precision
If cascade connection of unit filters is used to realize steep cut-off characteristic, then the filter performance improves, but the number of elements increases
Solution Approach 1:
Multiple unit filters are merged in a cascade connection, where each unit filter contributes to the overall steep cut-off characteristic. By combining these functional blocks, the patent achieves the desired manufacturing precision for the cut-off characteristic without excessively increasing the total number of elements through efficient design of each unit.
3Adaptability or versatility
If balanced terminals are required for filter device to match communication equipment, then the filter can be connected to frequency converter and amplifier, but the ladder structure provides unbalanced input and output
Solution Approach 1:
The patent employs asymmetric conversion circuits: a balanced-to-unbalanced converter at the input stage and a unbalanced-to-balanced converter at the output stage. This allows the filter to interface with balanced communication equipment while internally utilizing the simpler unbalanced ladder structure, thus achieving adaptability without excessive terminal configuration complexity.
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 lattice-type filter design enables the realization of high pass or low pass filters with balanced input and output, achieving a steep cut-off characteristic with a minimal number of elements, suitable for communication equipment, and allowing for miniaturization and reduced signal loss across the specified frequency bands.
Implementation Method 1
a lattice-type filter circuit having a resonator... a first resonator being connected to a series arm... a second resonator being connected to a series arm... a first resonant circuit including impedance elements... a second resonant circuit including impedance elements
Data Source
AI summary
A lattice-type filter circuit includes first and second balanced signal terminals; first and second balanced signal terminals; a first resonator connected to a series arm between the first balanced signal terminal on the input side and the first balanced signal terminal on the output side; a second resonator connected to a series arm between the second balanced signal terminal on the input side and the second balanced signal terminal on the output side; a first resonant circuit including impedance elements, being connected to a lattice arm between the first balanced signal terminal on the output side and the second balanced signal terminal on the input side; and a second resonant circuit including impedance elements, being connected to a lattice arm between the second balanced signal terminal on the output side and the first balanced signal terminal on the input side.