Composite Filter Layout Using 90° Hybrids to Cancel IMD
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Solution Overview
Problem
Existing composite filters, such as duplexers, suffer from nonlinear distortion due to inter-modulation distortion (IMD) in transmission and reception filters, which degrade the filter's performance.
Innovation Solution
A composite filter design incorporating a first and second hybrid coupler, each composed of a 90° hybrid, with specific wiring line length differences to phase-shift and cancel out nonlinear distortions between reception filters, maintaining signal strength and reducing IMD.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If transmission filter and reception filter are used in composite filter, then signal filtering performance is improved, but nonlinear distortion (IMD) increases
Solution Approach 1:
The reception filter system is divided into two separate reception filters (first reception filter and second reception filter) with different frequency characteristics. By segmenting the reception path and combining their outputs through hybrid couplers, the system achieves better overall filtering performance while reducing nonlinear distortion through diversity combining.
Solution Approach 2:
The patent uses a composite filter structure combining transmission filter with multiple reception filters having different frequency responses. This composite configuration allows the system to leverage the advantages of each filter type, achieving improved signal filtering while the diverse frequency characteristics help mitigate nonlinear distortion effects.
2Object-generated harmful factors
If 90° hybrid coupler is added to reduce nonlinear distortion, then IMD is reduced, but device complexity increases
Solution Approach 1:
The 90° hybrid couplers serve multiple functions simultaneously: they combine signals from multiple reception filters, provide impedance matching, enable phase manipulation for distortion cancellation, and facilitate the overall signal routing. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity.
3Measurement precision
If wiring line length difference is controlled to be less than half of maximum filter dimension, then phase alignment is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a particular parameter range for wiring line length difference (less than half of the maximum dimension of the first filter). By defining this specific parameter constraint, the design achieves acceptable phase alignment while providing a practical manufacturing tolerance that balances performance requirements with fabrication capabilities.
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 design effectively cancels out nonlinear distortions, maintaining signal integrity by ensuring equivalent signal strengths and phases, thereby improving the overall performance of the composite filter.
Implementation Method 1
The first hybrid and the second hybrid are each composed of a 90° hybrid coupler. When a signal is inputted to one of the common terminal and the first terminal, signals whose phases are shifted by 90° from each other are distributed to the first filter and the second filter
Implementation Method 2
The distributed signals are made to be in-phase signals and outputted to the other of the common terminal and the first terminal. The design effectively cancels out nonlinear distortions, maintaining signal integrity by ensuring equivalent signal strengths and phases
Data Source
AI summary
A first filter and a second filter are connected to a first hybrid and a second hybrid such that, when a signal is inputted to one of a common terminal and a first terminal, signals whose phases are shifted by 90° from each other are distributed to the first filter and the second filter, and the distributed signals are made to be in-phase signals and outputted. A difference between the length of wiring line from the first hybrid to the first filter and the length of wiring line from the first hybrid to the second filter is less than half of a maximum dimension of the first filter. A difference between the length of wiring line from the second hybrid to the first filter and the length of wiring line from the second hybrid to the second filter is less than half of the maximum dimension of the first filter.