RF Switch Bypass Topology Balancing Low Loss and LNA Isolation
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Solution Overview
Problem
RF signal switching circuits face challenges in achieving low input insertion loss (IL) and noise figure (NF) while maintaining high isolation, especially when the low noise amplifier (LNA) is not active, and require flexibility in switching paths for tunable gain states and signal function applications.
Innovation Solution
The RF signal switch circuit design allows connection of RF input terminals to a Switch Output port in low loss or bypass modes, with the ability to isolate the bypass path from the target circuit, using a configuration of in-path, shunt, and bypass switches to minimize insertion loss and noise figure, and optionally incorporating a matching network integrated with the target circuit.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the LNA is made bypassable to provide signal path flexibility, then adaptability is improved, but isolation between the bypass path and LNA input matching network deteriorates
Solution Approach 1:
The signal path is divided into separate segments: the LNA path with its matching network and the bypass path. Isolation switches (series switch SI and shunt switch ShI) are placed between these segments to control coupling. This segmentation allows independent optimization of each path while providing controlled isolation when needed.
Solution Approach 2:
Isolation switches are introduced as intermediary elements between the LNA input matching network and the bypass path. These switches act as mediators that can couple or decouple the two paths as required, enabling both bypass functionality and isolation when the LNA is inactive.
2Loss of energy
If low insertion loss is achieved in the bypass path, then energy loss is reduced, but isolation from the LNA path deteriorates due to matching network coupling
Solution Approach 1:
The LNA input matching network is extracted as a separate functional block with defined input and output ports. By treating it as a distinct module, the bypass path can be designed to minimize coupling to this network while maintaining low insertion loss through proper switch placement and configuration.
Solution Approach 2:
Isolation switches serve as intermediary elements that prevent unwanted coupling between the bypass path and the LNA matching network. When closed, they provide isolation even when the bypass path has low insertion loss, resolving the contradiction between energy efficiency and isolation.
3Reliability
If the LNA input matching network is optimized for low noise figure, then signal quality is improved, but bypass path performance deteriorates due to impedance interaction
Solution Approach 1:
The system is segmented into the LNA processing path and the bypass path, with isolation switches controlling the interaction. This allows the LNA input matching network to be optimized for noise figure without adversely affecting bypass path performance, as the segments can be independently optimized when isolation is active.
Solution Approach 2:
The coupling between the LNA path and bypass path is made dynamic through controllable isolation switches. The system can adapt its configuration based on operational requirements: when the LNA is active, normal coupling exists; when bypass mode is needed, isolation switches are closed to prevent impedance interaction that would degrade bypass performance.
Data Source
AI summary
An RF signal switch circuit that allows connection of any of N radio frequency (RF) input terminals to a switch output port, either in a low loss mode, in a bypass mode, or, optionally, in a signal function mode. Embodiments of the invention allow for both a single switch in the series input path to a target circuit while still having the ability to isolate the bypass path from the target circuit. In the low loss and bypass mode, the circuit simultaneously exhibits low input insertion loss (and thus a low noise factor) and high bypass mode isolation.