RF Switch Bypass Topology Isolating LNA Matching Networks
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing RF signal switching circuits face challenges in achieving low input insertion loss (IL) and noise figure (NF) while maintaining high isolation of the bypass path from the low noise amplifier (LNA) input matching network, leading to degraded bypass path performance.
Innovation Solution
The RF signal switch circuit design incorporates a configuration with a single series switch in the input path and isolation shunt switches, allowing for complete isolation of the bypass path from the matching network in both in-circuit and bypass modes, using a hybrid or monolithic structure with optional integrated matching networks, and employing high-isolation 'T' type series/shunt/series bypass switches for enhanced isolation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the matching network is connected to the bypass path, then the LNA input matching is improved, but the bypass path insertion loss is degraded
Solution Approach 1:
The circuit is divided into separate in-circuit and bypass modes using independent switch paths. The in-circuit path contains the matching network and LNA, while the bypass path provides a direct connection. This segmentation allows each path to be optimized independently for its specific function.
Solution Approach 2:
Isolation switches are pre-positioned to automatically disconnect the matching network from the bypass path when bypass mode is selected. This preliminary isolation action prevents the matching network from affecting bypass performance before the bypass switch is activated.
2Reliability
If isolation switches are added before the matching network, then the bypass path isolation is improved, but the input insertion loss to the LNA is increased
Solution Approach 1:
Isolation switches are positioned as intermediary elements between the bypass path and the matching network, not in the direct LNA signal path. These switches mediate the connection by providing electrical isolation when needed, without introducing loss into the in-circuit path to the LNA.
Solution Approach 2:
The isolation function is extracted from the main LNA signal path and placed in the bypass path configuration. This allows isolation to be achieved independently of the in-circuit insertion loss, as the isolation switches only affect the bypass path when activated.
3Reliability
If multiple switches are used in the input path, then the bypass path isolation is improved, but the device complexity is increased
Solution Approach 1:
Each switch in the circuit performs multiple functions: the series switch provides both signal routing and isolation, while the shunt switch provides both grounding and isolation. This multi-functionality reduces the total number of switches needed compared to dedicated single-function switch arrangements.
Solution Approach 2:
The isolation function is merged with the existing series and shunt switches rather than requiring separate dedicated isolation switches. The same switches that route the signal also provide isolation when in the appropriate state, combining multiple functions into fewer components.
Data Source
Figure 1
Figure 2
Figure 3
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 an in-circuit mode or in a bypass mode. Embodiments of the invention allow for both a single switch in the series input path while still having the ability to isolate the bypass path from an input matching network. In both modes, the circuit simultaneously exhibits low input insertion loss (and thus a low noise factor) and high bypass mode isolation.