RF Front-End Circuit Layout Using SPDT Switching for Multi-Band Isolation
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Solution Overview
Problem
Radio frequency front-end circuits that allow selective passage of signals in multiple frequency bands require a large number of switch terminals, increasing circuit size and cost, while maintaining satisfactory attenuation and isolation characteristics.
Innovation Solution
A radio frequency front-end circuit with a Single Pole Double Throw (SPDT) switch and filter elements having non-overlapping pass bands, where the SPDT switch is placed between filter elements with overlapping pass bands, reducing the number of select terminals and enabling cost and size reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch with select terminals in the same number as frequency bands (SPnT type) is used to allow selective passage of radio frequency signals in three or more frequency bands, then the attenuation characteristics and isolation characteristics are satisfied, but the circuit size and cost are increased
Solution Approach 1:
The patent divides the frequency bands into two groups: overlapping frequency bands (handled by SPDT switch) and non-overlapping frequency bands (handled by direct connection). This segmentation allows different switching strategies for different frequency band relationships, reducing the overall switch complexity from SPnT to SPDT while maintaining performance
Solution Approach 2:
The SPDT switch is designed to handle multiple frequency band combinations by selectively connecting to different filter elements based on the desired frequency band. The same switch structure serves universal purposes for managing both overlapping and non-overlapping frequency bands through proper configuration
2Adaptability or versatility
If three or more filter elements with different pass bands are connected to an antenna common terminal through an SPnT switch, then selective signal passage in multiple frequency bands is achieved, but the number of select terminals increases leading to larger circuit size
Solution Approach 1:
The patent segments the filter elements into two categories: those connected through the SPDT switch (for overlapping bands) and those connected directly to the antenna terminal (for non-overlapping bands). This reduces the number of switch terminals needed while maintaining the ability to selectively pass signals in multiple frequency bands
Solution Approach 2:
Instead of connecting all filter elements through a high-terminal-count switch, the patent inverts the approach by directly connecting some filter elements to the antenna terminal and using the switch only where necessary for overlapping bands, thereby reducing the switch terminal count
Data Source
AI summary
An RF front-end circuit (2) includes an antenna common terminal (20) connected to an antenna element (1), an SPDT switch circuit (21) having a common terminal (21c) and select terminals (21s1 and 21s2), and four filter elements (22A to 22D). The common terminal (21c) and the filter elements (22C and 22D) are connected to the antenna common terminal (20). The filter elements (22A and 22B) are connected to the select terminals (21s1 and 21s2), respectively. Pass bands of the filter elements (22A, 22C and 22D) do not overlap with one another, and pass bands of the filter elements (22B, 22C and 22D) do not overlap with one another. The pass bands of the filter elements (22A and 22B) partly overlap with each other.