RF Switch Shunt Impedance Matching to Minimize Signal Reflection
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Solution Overview
Problem
RF switches in existing RF circuits reflect RF signals when turned off, leading to abnormal operation and degraded signal quality.
Innovation Solution
The RF switch design includes a shunt switch path with sub-shunt circuits comprising stacked transistors and resistors, allowing for controlled impedance states to match load resistance when turned off, minimizing signal reflection by providing an equivalent resistance equal to the load resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the RF switch is turned off using conventional design, then the switch can block RF signal transmission, but signal reflection occurs causing abnormal operation
Solution Approach 1:
The patent changes the impedance parameter of the switch by adding a shunt switch path with variable impedance (first, second, and third impedance states). When the switch is turned off, the shunt path provides a third impedance state that matches the load resistance, transforming the harmful reflection into a matched termination condition.
Solution Approach 2:
The shunt switch path acts as an intermediary element between the main switch path and the load. It provides an alternative current path with controlled impedance that mediates the signal flow when the main switch is off, preventing direct reflection at the switch terminals.
2Object-generated harmful factors
If impedance matching components are added to reduce signal reflection, then signal quality improves, but circuit area increases
Solution Approach 1:
The shunt switch path serves multiple functions simultaneously: it provides impedance matching to reduce reflection, maintains signal quality, and integrates into the existing switch structure without requiring separate external matching components. This multi-functionality achieves impedance matching within the compact switch footprint.
Solution Approach 2:
The patent merges the impedance matching function with the switching function by integrating the shunt switch path directly into the switch structure. The same control mechanism that switches the main path also controls the shunt path, combining multiple functions into a unified compact structure.
Data Source
AI summary
A radio frequency (RF) switch includes a signal terminal, a reference voltage terminal and a shunt switch path. The shunt switch path includes a first sub-shunt circuit and a second sub-shunt circuit. The second sub-shunt circuit includes a first transistor and a second transistor coupled in parallel. When switched to a first state, the RF switch has first impedance; when switched to a second state, the RF switch has second impedance; and when switched to a third state, the RF switch has third impedance. The first impedance, the second impedance, and the third impedance are different.