RF Front-End Filter Switching for Overlapping Band Leakage
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Solution Overview
Problem
Existing filter devices for radio-frequency front-end circuits in multi-band and multi-mode cellular phones face challenges in maintaining good filter characteristics while keeping the device compact, as the overlap of pass bands between filters can lead to deterioration of attenuation characteristics due to signal leakage.
Innovation Solution
A filter device with a common terminal and multiple filters, where a switch circuit switches between different filter connections, allowing one filter to have a higher insertion loss in overlapping bands, thereby reducing signal leakage and maintaining filter characteristics without the need for increased switch circuit size.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the isolation of the filter switching switch is enhanced to prevent signal leakage, then the filter characteristics are improved, but the device size increases
Solution Approach 1:
The patent applies preliminary action by configuring the second filter to have high insertion loss in the overlapping frequency band before switching occurs. This pre-configuration ensures that even when the switch has limited isolation, the second filter inherently suppresses signals in the overlapping band, preventing signal leakage to the first filter without requiring enhanced switch isolation
Solution Approach 2:
The patent applies local quality by making the second filter have non-uniform insertion loss characteristics - specifically, high insertion loss in the overlapping frequency band where it conflicts with the first filter, while maintaining low insertion loss in its own pass band. This localized quality adjustment allows the second filter to suppress signals only where needed without affecting overall system performance
2Adaptability or versatility
If multiple filters are connected to a common terminal to support multi-band, then the adaptability is improved, but the signal leakage between filters deteriorates the attenuation characteristics
Solution Approach 1:
The patent applies local quality by configuring the second filter to have high insertion loss specifically in the overlapping frequency band, creating a localized suppression zone that prevents signal leakage only where frequency bands overlap, while maintaining normal filter performance in non-overlapping bands
Solution Approach 2:
The patent converts the potentially harmful effect of the second filter's pass band overlapping with the first filter's attenuation band into a benefit by deliberately designing the second filter to have high insertion loss in that overlapping region, thereby using the overlapping configuration itself to achieve signal suppression rather than requiring separate isolation mechanisms
Data Source
AI summary
A filter device includes a filter (22A) connected to a common terminal (110) and having a first characteristic, a variable filter (22B) connected to the common terminal (110) and capable of changing a characteristic to one of a second characteristic and a third characteristic, and a switch (23). In the second characteristic, a second pass band including an overlapping band in which the second pass band and an attenuation band of the filter (22A) partially overlap in frequency is defined. Insertion loss within the overlapping band for the third characteristic is greater than insertion loss within the overlapping band for the second characteristic. When the filter (22A) is selected by the switch (23), the characteristic of the variable filter (22B) is set to the third characteristic.