Asymmetric Cascode Transistor for RF Power Amplifiers
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Solution Overview
Problem
Conventional RF power amplifier circuits in wireless communication devices face challenges in achieving high frequency performance and power efficiency due to the use of high voltage cascode transistors, which result in high series resistance and reliability issues.
Innovation Solution
The implementation of a high performance asymmetric cascode transistor with a source extension diffusion and pocket implant to set a high turn on voltage, reducing series resistance and improving frequency performance, while also optimizing the drain extension independently to meet high voltage specifications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a high voltage cascode transistor with thick gate oxide is used to withstand high voltage, then voltage capability is improved, but series resistance increases and frequency performance deteriorates
Solution Approach 1:
The patent applies different gate oxide thicknesses to different regions of the cascode transistor. The gate oxide is thinner in the channel region to reduce series resistance and improve frequency performance, while being thicker in the drain region to withstand high voltage stress. This local differentiation resolves the contradiction between voltage capability and frequency performance.
Solution Approach 2:
The patent introduces asymmetric structure to the cascode transistor by having different gate oxide thicknesses at different locations (thin at source/channel, thick at drain). This asymmetric design allows the transistor to simultaneously achieve low series resistance for high frequency operation and high voltage breakdown capability, directly resolving the technical contradiction.
2Speed
If the gate oxide is made thinner to reduce series resistance, then frequency performance is improved, but voltage withstand capability deteriorates
Solution Approach 1:
The patent implements local quality by varying gate oxide thickness within the same transistor structure. The channel region has thin gate oxide for low resistance and high frequency response, while the drain region has thick gate oxide for high voltage withstand capability. This spatial differentiation resolves the contradiction between speed and strength.
3Strength
If conventional high voltage transistor design is used, then voltage capability is achieved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent merges the high voltage cascode transistor and the gain transistor into a single integrated structure with a shared substrate and integrated doping regions. The asymmetric cascode transistor shares the common diffusion with the gain transistor, reducing the number of separate components and simplifying manufacturing processes while maintaining voltage capability.
Solution Approach 2:
The patent creates a multi-functional transistor structure where the asymmetric cascode transistor serves multiple purposes: it provides high voltage withstand capability through its thick drain gate oxide, maintains low series resistance through thin channel gate oxide for high frequency operation, and integrates with the gain transistor to form a complete power amplifier stage. This universality reduces overall device complexity.
Data Source
AI summary
An integrated circuit with a LV transistor and a high performance asymmetric transistor. A power amplifier integrated circuit with a core transistor and a high performance asymmetric transistor. A method of forming an integrated circuit with a core transistor and a high performance asymmetric transistor. A method of forming a power amplifier integrated circuit with an nmos core transistor and an nmos high performance asymmetric transistor, a resistor, and an inductor.