RF Multiplexer Bypass Switching for Low Loss and Isolation
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Solution Overview
Problem
Existing radio frequency multiplexers face challenges in reducing loss in the pass band while maintaining isolation due to the on-resistance of switches used in the main signal path.
Innovation Solution
A multiplexer configuration that includes a demultiplexing circuit with impedance circuits and a switch circuit, where the switch connects nodes to ground with impedance circuits interposed, allowing for reduced loss in the pass band while securing isolation by adjusting impedance to match normalized impedance or zero/infinity conditions for specific frequency bands.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a switch is provided on the main path for transmitting the radio frequency signal between the input terminal and the output terminal to secure isolation, then isolation is improved, but loss in the pass band increases due to on-resistance of the switch
Solution Approach 1:
The switch is extracted from the main signal path and relocated to a bypass path. The main path now consists only of the filter, eliminating switch-induced loss. The switch operates in parallel, connecting to ground through an impedance circuit, thereby maintaining isolation functionality without degrading pass band performance.
Solution Approach 2:
An impedance circuit is introduced as an intermediary element between the switch and ground. This impedance circuit enables the switch to provide effective isolation by controlling the impedance state (matching normalized impedance or presenting zero/infinity) for specific frequency bands, while minimizing its impact on the main signal path.
2Loss of energy
If the switch is removed from the main path to reduce loss, then loss in the pass band is reduced, but isolation deteriorates
Solution Approach 1:
The circuit is segmented into a main signal path and a bypass path. The main path handles signal transmission with minimal components (only the filter), while the bypass path contains the switch and impedance circuit for isolation control. This segmentation allows each path to be optimized independently for its specific function.
Solution Approach 2:
The impedance circuit dynamically changes its impedance parameter based on the operating frequency band. By adjusting the impedance state (matching normalized impedance or presenting zero/infinity), the switch in the bypass path can provide effective isolation without interfering with the main signal path, thereby maintaining both low loss and high isolation.
Data Source
AI summary
A multiplexer (1) includes: a demultiplexing circuit (11) including a common terminal (110c) and individual terminals (111 and 112); a filter (21) connected to the individual terminal (111); and a filter (22) connected to the individual terminal (112). The demultiplexing circuit (11) further includes an impedance circuit (Z1) provided in series on a path (r1) connecting the common terminal (110c) and the individual terminal (111), an impedance circuit (Z2) provided in series on a path (r2) connecting the common terminal (110c) and the individual terminal (112), and an impedance circuit (Z3) and a switch circuit (12). The switch circuit (12) connects only one of a node (N1) on the path (r1) between the impedance circuit (Z1) and the individual terminal (111) and a node (N2) on the path (r2) between the impedance circuit (Z2) and the individual terminal (112) to a ground with the impedance circuit (Z3) interposed therebetween.