Stacked MOS Switch Biasing for RF Isolation and Reliability
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Solution Overview
Problem
Switches in wireless communication devices, particularly those implemented with MOS transistors, face performance issues due to parasitic capacitances that lead to signal loss and reliability concerns, especially when handling RF signals and experiencing large signal swings.
Innovation Solution
The implementation of switches with stacked MOS transistors and additional RF floating resistors to reduce signal loss and improve reliability by distributing the signal swing evenly across multiple transistors, enhancing isolation and reducing the impact of parasitic capacitances.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single MOS transistor is used to implement a switch, then the device complexity is low, but parasitic capacitances cause signal loss and reduced reliability
Solution Approach 1:
The patent divides a single transistor into multiple stacked transistors (e.g., two or more MOS transistors connected in series). This segmentation reduces the parasitic capacitance impact on each individual transistor, thereby improving switch reliability and signal loss characteristics while distributing the voltage stress across multiple devices.
Solution Approach 2:
The patent introduces intermediate biasing circuits and control mechanisms between the stacked transistors. These intermediary elements manage the voltage distribution and switching control, enabling the stacked configuration to function effectively while maintaining improved reliability without excessive complexity.
2Loss of energy
If stacked MOS transistors are used to reduce parasitic capacitance impact, then signal loss is reduced and reliability is improved, but device complexity increases
Solution Approach 1:
By segmenting the switch into multiple stacked transistors, the patent reduces the parasitic capacitance effect on signal loss for each transistor. The segmented configuration allows better signal transmission while distributing the electrical stress, thereby reducing overall signal loss despite the increased number of components.
3Reliability
If stacked MOS transistors are used to distribute signal swing, then reliability is improved, but the number of components increases
Solution Approach 1:
The patent employs segmentation by using multiple stacked transistors to divide the voltage swing distribution. Each transistor in the stack handles a portion of the total voltage swing, which improves reliability by preventing any single transistor from experiencing excessive stress, while the increased quantity of transistors is justified by the reliability gains.
Data Source
AI summary
Switches with improved biasing and having better isolation and reliability are described. In an exemplary design, a switch is implemented with a set of transistors, a set of resistors, and an additional resistor. The set of transistors is coupled in a stacked configuration, receives an input signal, and provides an output signal. The set of resistors is coupled to the gates of the set of transistors. The additional resistor is coupled to the set of resistors and receives a control signal for the set of transistors. The resistors reduce signal loss through parasitic capacitances of the transistors when they are turned on. The resistors also help split the signal swing of the input signal approximately evenly across the transistors when they are turned off, which may improve reliability of the transistors. The switch may be used in a switchplexer, a power amplifier (PA) module, etc.