Switchable Receive Filter in FDD RF Circuits for Harmonic Jamming
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Solution Overview
Problem
In high-frequency signal transmission-reception circuits, particularly in mobile communication terminals, simultaneous transmission and reception using a single antenna can lead to deterioration of reception sensitivity due to harmonic components from the transmission signal being superimposed on the reception path, especially in frequency division duplex (FDD) schemes.
Innovation Solution
A high-frequency signal transmission-reception circuit is designed with a multiplexer that separates transmission and reception paths, incorporating a filter circuit capable of switching between two distinct frequency responses based on received jamming waves, using a sub-controller to adjust the filter's frequency response to mitigate the impact of harmonic components during transmission operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a SAW multiplexer is used to separate transmission and reception paths in FDD scheme, then transmission and reception can be performed simultaneously, but harmonic components of transmission signal are superimposed on reception path causing deterioration of reception sensitivity
Solution Approach 1:
The reception path is segmented into multiple filter sections: a first filter (SAW filter) that passes reception frequency bands and blocks transmission frequency bands, and a second filter (LC filter or other type) that specifically blocks harmonic components of the transmission signal. This segmentation allows each filter to address specific interference sources independently, resolving the contradiction between simultaneous transmission-reception capability and reception sensitivity.
Solution Approach 2:
An additional filter (second filter) is introduced as an intermediary element between the SAW multiplexer and the reception signal processing chain. This intermediary filter specifically targets and blocks harmonic components that pass through the SAW multiplexer, thereby protecting the reception path from harmonic interference while maintaining the simultaneous transmission-reception functionality provided by the SAW multiplexer.
2Reliability
If a switch element or filter element blocking harmonic components is provided in TDD scheme transmission path, then harmonic components are kept from flowing into reception signal path, but this increases device complexity
Solution Approach 1:
The first filter (SAW filter) serves multiple functions: it acts as the primary frequency selective element for the SAW multiplexer operation and simultaneously provides initial blocking of transmission frequency bands and their harmonics. The second filter complements this by providing specialized harmonic blocking. This multi-functional design achieves comprehensive harmonic rejection without requiring complex switching mechanisms, thereby reducing device complexity compared to TDD方案的开关元件.
Data Source
AI summary
A high-frequency circuit includes a transmission circuit that transmits a high-frequency signal, a reception circuit that receives a high-frequency signal, and a multiplexer that separates a reception path and a transmission path for high-frequency signals. In the reception circuit, a filter circuit in which a first frequency response and a second frequency response different from the first frequency response can be switched in accordance with a jamming wave for a high-frequency signal to be received is provided in the reception path for a high-frequency signal.